Re: [build, driver] RFC: Support compressed debug sections

Re: [build, driver] RFC: Support compressed debug sections

[Andi Kleen]

Rainer Orth <ro@CeBiTec.Uni-Bielefeld.DE> writes:

> There's some interest inside Oracle to support compressed debug sections
> inside their toolchain, both on Solaris and Linux.  So far, there's the
> GNU style supported by gas, gld, gold, and gdb, which mangles section
> names (.debug_* -> .zdebug_*), but consultation with the Solaris linker
> engineers resulted in a different style, now (almost) approved for the
> ELF gABI.  The final proposal can be found here:
>
> https://groups.google.com/forum/#!msg/generic-abi/dBOS1H47Q64/Fm_Jh9vOlG8J

None of the messages explains why the new format is better than the
existing one. For GNU this seems to have zero value.

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only

[build, driver] RFC: Support compressed debug sections

[Rainer Orth]

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There's some interest inside Oracle to support compressed debug sections
inside their toolchain, both on Solaris and Linux.  So far, there's the
GNU style supported by gas, gld, gold, and gdb, which mangles section
names (.debug_* -> .zdebug_*), but consultation with the Solaris linker
engineers resulted in a different style, now (almost) approved for the
ELF gABI.  The final proposal can be found here:

https://groups.google.com/forum/#!msg/generic-abi/dBOS1H47Q64/Fm_Jh9vOlG8J

I've now started to implement this for gcc and probably other parts of
the GNU toolchain.  This patch proposes to add a

	-gz[=none|zlib|zlib-gnu]

option to gcc, enabling (or disabling) compressed debug sections in
either format, and passing the necessary options to assembler and/or
linker.

It probably has rough edges since this is the first time I've been
dealing with the option handling machinery, and may or may not be
appropriate for approval at this time.

I'm asking for both comments on the general approach and specific review
comments.

So far, the patch has been tested on i386-pc-solaris2.11 with gas 2.23.2
and a version of the Solaris linker that supports -z compress-debug-sections.

	Rainer


2013-04-10  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	* configure.ac (gcc_cv_as_compress_debug): Check for assembler
	compressed debug support.
	(gcc_cv_ld_compress_debug): Check for linker compressed debug
	support.
	* configure: Regenerate.
	* config.in: Regenerate.
	* common.opt (gz, gz=): New options.
	* gcc.c (LINK_COMPRESS_DEBUG_SPEC, ASM_COMPRESS_DEBUG_SPEC):
	Define.
	(LINK_COMMAND_SPEC): Invoke LINK_COMPRESS_DEBUG_SPEC.
	(asm_options): Invoke ASM_COMPRESS_DEBUG_SPEC.
	* opts.c (common_handle_option): Handle OPT_gz, OPT_gz_.
	* doc/invoke.texi (Option Summary, Debugging Options): Add
	-gz[=type].
	(Debugging Options): Document -gz[=type].


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# HG changeset patch
# Parent 6d495f6205ff6ab3888d907d7891cce8f7593878
Enable --compress-debug-sections

diff --git a/gcc/common.opt b/gcc/common.opt
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -2375,6 +2375,14 @@ gxcoff+
 Common JoinedOrMissing Negative(gcoff)
 Generate debug information in extended XCOFF format
 
+gz
+Common Driver
+Generate compressed debug sections
+
+gz=
+Common Driver JoinedOrMissing
+-gz=<format>	Generate compressed debug sections in format <format>
+
 h
 Driver Joined Separate
 
diff --git a/gcc/configure.ac b/gcc/configure.ac
--- a/gcc/configure.ac
+++ b/gcc/configure.ac
@@ -4261,6 +4261,27 @@ if test x"$insn" != x; then
 [Define if your assembler supports the --debug-prefix-map option.])])
 fi
 
+gcc_GAS_CHECK_FEATURE([compressed debug sections],
+  gcc_cv_as_compress_debug,, [--compress-debug-sections],,
+  [# gas compiled without zlib cannot compress debug sections and warns
+   # about it, but still exits successfully.  So check for this.
+   if AC_TRY_COMMAND([$gcc_cv_as --compress-debug-sections -o conftest.o conftest.s 2>&1 | grep -i warning > /dev/null])
+   then
+     gcc_cv_as_compress_debug=0
+   else
+     gcc_cv_as_compress_debug=1
+     gcc_cv_as_compress_debug_option="--compress-debug-sections"
+     gcc_cv_as_no_compress_debug_option="--nocompress-debug-sections"
+   # FIXME: Future gas versions will support ELF gABI style via
+   # --compress-debug-sections[=type].
+   fi])
+AC_DEFINE_UNQUOTED(HAVE_AS_COMPRESS_DEBUG, $gcc_cv_as_compress_debug,
+[Define to the level of your assembler's compressed debug section support.])
+AC_DEFINE_UNQUOTED(AS_COMPRESS_DEBUG_OPTION, "$gcc_cv_as_compress_debug_option",
+[Define to the assembler option to enable compressed debug sections.])
+AC_DEFINE_UNQUOTED(AS_NO_COMPRESS_DEBUG_OPTION, "$gcc_cv_as_no_compress_debug_option",
+[Define to the assembler option to disable compressed debug sections.])
+
 gcc_GAS_CHECK_FEATURE([.lcomm with alignment], gcc_cv_as_lcomm_with_alignment,
  ,,
 [.lcomm bar,4,16],,
@@ -4531,6 +4552,56 @@ if test x$gcc_cv_ld_eh_gc_sections_bug =
 fi
 AC_MSG_RESULT($gcc_cv_ld_eh_gc_sections_bug)
 
+# gold/gld support compressed debug sections since binutils 2.19/2.21
+if test $in_tree_ld = yes ; then
+  gcc_cv_ld_compress_debug=0
+  if test "$gcc_cv_gld_major_version" -eq 2 -a "$gcc_cv_gld_minor_version" -ge 19 -o "$gcc_cv_gld_major_version" -gt 2 \
+     && test $in_tree_ld_is_elf = yes && test $ld_is_gold = yes; then
+    gcc_cv_ld_compress_debug=2
+    gcc_cv_ld_compress_debug_option="--compress-debug-sections"
+  elif test "$gcc_cv_gld_major_version" -eq 2 -a "$gcc_cv_gld_minor_version" -ge 21 -o "$gcc_cv_gld_major_version" -gt 2 \
+     && test $in_tree_ld_is_elf = yes; then
+    gcc_cv_ld_compress_debug=1
+  fi
+elif echo "$ld_ver" | grep GNU > /dev/null; then
+  gcc_cv_ld_compress_debug=1
+  if test 0"$ld_date" -lt 20050308; then
+    if test -n "$ld_date"; then
+      # If there was date string, but was earlier than 2005-03-08, fail
+      gcc_cv_ld_compress_debug=0
+    elif test "$ld_vers_major" -lt 2; then
+      gcc_cv_ld_compress_debug=0
+    elif test "$ld_vers_major" -eq 2 -a "$ld_vers_minor" -lt 21; then
+      gcc_cv_ld_compress_debug=0
+    fi
+  fi
+  if test $ld_is_gold = yes; then
+    gcc_cv_ld_compress_debug=2
+    gcc_cv_ld_compress_debug_option="--compress-debug-sections"
+  fi
+else
+changequote(,)dnl
+  case "${target}" in
+    *-*-solaris2*)
+      # Introduced in Solaris 11.2.
+      if $gcc_cv_ld --help 2>&1 | grep -- '-z compress-debug-sections' > /dev/null; then
+        gcc_cv_ld_compress_debug=3
+        gcc_cv_ld_compress_debug_option="-z compress-debug-sections"
+      fi
+      ;;
+    *)
+      # Assume linkers other than GNU ld don't support compessed debug
+      # sections.
+      gcc_cv_ld_compress_debug=0
+      ;;
+  esac
+changequote([,])dnl
+fi
+AC_DEFINE_UNQUOTED(HAVE_LD_COMPRESS_DEBUG, $gcc_cv_ld_compress_debug,
+[Define to the level of your linker's compressed debug section support.])
+AC_DEFINE_UNQUOTED(LD_COMPRESS_DEBUG_OPTION, "$gcc_cv_ld_compress_debug_option",
+[Define to the linker option to enable compressed debug sections.])
+
 # --------
 # UNSORTED
 # --------
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -337,7 +337,7 @@ Objective-C and Objective-C++ Dialects}.
 -g  -g@var{level}  -gtoggle  -gcoff  -gdwarf-@var{version} @gol
 -ggdb  -grecord-gcc-switches  -gno-record-gcc-switches @gol
 -gstabs  -gstabs+  -gstrict-dwarf  -gno-strict-dwarf @gol
--gvms  -gxcoff  -gxcoff+ @gol
+-gvms  -gxcoff  -gxcoff+ -gz@r{[}=@var{type}@r{]} @gol
 -fno-merge-debug-strings -fno-dwarf2-cfi-asm @gol
 -fdebug-prefix-map=@var{old}=@var{new} @gol
 -femit-struct-debug-baseonly -femit-struct-debug-reduced @gol
@@ -4999,6 +4999,15 @@ DWARF extensions from later standard ver
 Allow using extensions of later DWARF standard version than selected with
 @option{-gdwarf-@var{version}}.
 
+@item -gz@r{[}=@var{type}@r{]}
+@opindex gz
+Produce compressed debug sections in DWARF format (if that is
+supported).  If @var{type} is not given, the default type depends on the
+capabilities of the assembler and linker used.  @var{type} may be one of
+@option{none} (don't compress debug sections), @option{zlib} (use zlib
+compression in ELF gABI format), or @option{zlib-gnu} (use zlib
+compression in tradition GNU format).
+
 @item -gvms
 @opindex gvms
 Produce debugging information in Alpha/VMS debug format (if that is
diff --git a/gcc/gcc.c b/gcc/gcc.c
--- a/gcc/gcc.c
+++ b/gcc/gcc.c
@@ -586,6 +586,31 @@ proper position among the other output f
 #define LIBTSAN_EARLY_SPEC ""
 #endif
 
+/* Linker options for compressed debug sections.  */
+#if HAVE_LD_COMPRESS_DEBUG == 0
+/* No linker support.  */
+#define LINK_COMPRESS_DEBUG_SPEC \
+	" %{gz*:%e-gz is not supported in this configuration}"
+#elif HAVE_LD_COMPRESS_DEBUG == 1
+/* GNU style, GNU ld options.  */
+#define LINK_COMPRESS_DEBUG_SPEC \
+	" %{gz|gz=zlib-gnu:}" \
+	" %{gz=none:%e-gz=none is not supported in this configuration}" \
+	" %{gz=zlib:%e-gz=zlib is not supported in this configuration}"
+#elif HAVE_LD_COMPRESS_DEBUG == 2
+/* GNU style, GNU gold options.  */
+#define LINK_COMPRESS_DEBUG_SPEC \
+	" %{gz|gz=zlib-gnu:" LD_COMPRESS_DEBUG_OPTION "=zlib}" \
+	" %{gz=none:"        LD_COMPRESS_DEBUG_OPTION "=none}" \
+	" %{gz=zlib:%e-gz=zlib is not supported in this configuration}"
+#else
+/* ELF gABI style.  */
+#define LINK_COMPRESS_DEBUG_SPEC \
+	" %{gz|gz=zlib:"  LD_COMPRESS_DEBUG_OPTION "=zlib}" \
+	" %{gz=none:"	  LD_COMPRESS_DEBUG_OPTION "=none}" \
+	" %{gz=zlib-gnu:" LD_COMPRESS_DEBUG_OPTION "=zlib-gnu}"
+#endif
+
 /* config.h can define LIBGCC_SPEC to override how and when libgcc.a is
    included.  */
 #ifndef LIBGCC_SPEC
@@ -620,6 +645,25 @@ proper position among the other output f
 #define ASM_MAP ""
 #endif
 
+/* Assembler options for compressed debug sections.  */
+#if HAVE_AS_COMPRESS_DEBUG == 0
+/* No assembler support.  */
+#define ASM_COMPRESS_DEBUG_SPEC \
+	" %{gz*:%e-gz is not supported in this configuration}"
+#elif HAVE_AS_COMPRESS_DEBUG == 1
+/* GNU style, GNU as options.  */
+#define ASM_COMPRESS_DEBUG_SPEC \
+	" %{gz|gz=zlib-gnu:" AS_COMPRESS_DEBUG_OPTION "}" \
+	" %{gz=none:"        AS_NO_COMPRESS_DEBUG_OPTION "}" \
+	" %{gz=zlib:%e-gz=zlib is not supported in this configuration}"
+#else
+/* ELF gABI style.  */
+#define ASM_COMPRESS_DEBUG_SPEC \
+	" %{gz|gz=zlib:"  AS_COMPRESS_DEBUG_OPTION "=zlib}" \
+	" %{gz=none:"	  AS_COMPRESS_DEBUG_OPTION "=none}" \
+	" %{gz=zlib-gnu:" AS_COMPRESS_DEBUG_OPTION "=zlib-gnu}"
+#endif
+
 /* Define ASM_DEBUG_SPEC to be a spec suitable for translating '-g'
    to the assembler.  */
 #ifndef ASM_DEBUG_SPEC
@@ -737,8 +781,8 @@ proper position among the other output f
     LINK_PLUGIN_SPEC \
    "%{flto|flto=*:%<fcompare-debug*} \
     %{flto} %{flto=*} %l " LINK_PIE_SPEC \
-   "%{fuse-ld=*:-fuse-ld=%*}\
-    %X %{o*} %{e*} %{N} %{n} %{r}\
+   "%{fuse-ld=*:-fuse-ld=%*} " LINK_COMPRESS_DEBUG_SPEC \
+   "%X %{o*} %{e*} %{N} %{n} %{r}\
     %{s} %{t} %{u*} %{z} %{Z} %{!nostdlib:%{!nostartfiles:%S}}\
     %{static:} %{L*} %(mfwrap) %(link_libgcc) " SANITIZER_EARLY_SPEC " %o\
     %{fopenmp|ftree-parallelize-loops=*:%:include(libgomp.spec)%(link_gomp)}\
@@ -865,6 +909,7 @@ static const char *asm_options =
    to the assembler equivalents.  */
 "%{v} %{w:-W} %{I*} "
 #endif
+ASM_COMPRESS_DEBUG_SPEC
 "%a %Y %{c:%W{o*}%{!o*:-o %w%b%O}}%{!c:-o %d%w%u%O}";
 
 static const char *invoke_as =
diff --git a/gcc/opts.c b/gcc/opts.c
--- a/gcc/opts.c
+++ b/gcc/opts.c
@@ -1732,6 +1732,11 @@ common_handle_option (struct gcc_options
 		       loc);
       break;
 
+    case OPT_gz:
+    case OPT_gz_:
+      /* Handled completely via specs.  */
+      break;
+
     case OPT_pedantic_errors:
       dc->pedantic_errors = 1;
       control_warning_option (OPT_Wpedantic, DK_ERROR, value,

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-- 
-----------------------------------------------------------------------------
Rainer Orth, Center for Biotechnology, Bielefeld University

Re: [build, driver] RFC: Support compressed debug sections

[Rainer Orth]

Andi Kleen <andi@firstfloor.org> writes:

> Rainer Orth <ro@CeBiTec.Uni-Bielefeld.DE> writes:
>
>> There's some interest inside Oracle to support compressed debug sections
>> inside their toolchain, both on Solaris and Linux.  So far, there's the
>> GNU style supported by gas, gld, gold, and gdb, which mangles section
>> names (.debug_* -> .zdebug_*), but consultation with the Solaris linker
>> engineers resulted in a different style, now (almost) approved for the
>> ELF gABI.  The final proposal can be found here:
>>
>> https://groups.google.com/forum/#!msg/generic-abi/dBOS1H47Q64/Fm_Jh9vOlG8J
>
> None of the messages explains why the new format is better than the
> existing one. For GNU this seems to have zero value.

It's at the beginning of the first message.  Besides, if you look at
binutils sources with several large tables mapping .debug_* to .zdebug_*
sections, there's lots of complexitiy involved in the traditional
format and the name mangling involved.

Anyway, this is now part of the gABI, and the patch at hand also works
with the old GNU style (-gz=zlib-gnu), so it has value even when the
gABI style isn't supported.  Having users invoke gcc
-Wa,--compress-debug-sections -Wl,--compress-debug-sections instead of
-gz doesn't seem to be a good user interface to me.

	Rainer

-- 
-----------------------------------------------------------------------------
Rainer Orth, Center for Biotechnology, Bielefeld University

Re: [build, driver] RFC: Support compressed debug sections

[Joseph S. Myers]

On Thu, 11 Apr 2013, Rainer Orth wrote:

> +gz=
> +Common Driver JoinedOrMissing
> +-gz=<format>	Generate compressed debug sections in format <format>

Although handled entirely in specs, I think it's best to use the Enum .opt 
facility to list the valid arguments to this option, so the option 
handling machinery can properly detect invalid arguments.  (And, since an 
empty argument isn't meaningful, use Joined rather than JoinedOrMissing.)

The integer values assigned to each valid argument string are of course 
arbitrary since nothing will use them.

> +@item -gz@r{[}=@var{type}@r{]}
> +@opindex gz
> +Produce compressed debug sections in DWARF format (if that is
> +supported).  If @var{type} is not given, the default type depends on the
> +capabilities of the assembler and linker used.  @var{type} may be one of
> +@option{none} (don't compress debug sections), @option{zlib} (use zlib
> +compression in ELF gABI format), or @option{zlib-gnu} (use zlib
> +compression in tradition GNU format).

"traditional".

-- 
Joseph S. Myers
joseph@codesourcery.com

Re: [build, driver] RFC: Support compressed debug sections

[Rainer Orth]

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"Joseph S. Myers" <joseph@codesourcery.com> writes:

> On Thu, 11 Apr 2013, Rainer Orth wrote:
>
>> +gz=
>> +Common Driver JoinedOrMissing
>> +-gz=<format>	Generate compressed debug sections in format <format>
>
> Although handled entirely in specs, I think it's best to use the Enum .opt 
> facility to list the valid arguments to this option, so the option 
> handling machinery can properly detect invalid arguments.  (And, since an 

I already wondered how to do this with specs, but your suggestion worked
seamlessly, thanks.

> empty argument isn't meaningful, use Joined rather than JoinedOrMissing.)

Done.  This was a leftover from a failed attempt to handle -gz[=format]
in a single clause.

> The integer values assigned to each valid argument string are of course 
> arbitrary since nothing will use them.

Right, so I've just used numeric constants.

>> +@item -gz@r{[}=@var{type}@r{]}
>> +@opindex gz
>> +Produce compressed debug sections in DWARF format (if that is
>> +supported).  If @var{type} is not given, the default type depends on the
>> +capabilities of the assembler and linker used.  @var{type} may be one of
>> +@option{none} (don't compress debug sections), @option{zlib} (use zlib
>> +compression in ELF gABI format), or @option{zlib-gnu} (use zlib
>> +compression in tradition GNU format).
>
> "traditional".

Fixed.

The patch now underwent additonal testing on i386-pc-solaris2.11.  The
following tools were handled correctly:

* Solaris as: not yet capable of generating compressed debug sections.
  Planned, but command line options not yet known.

* GNU as 2.23.1 built without zlib: just warns about
  --compressed-debug-sections, but exits successfully.

* GNU as 2.23.2 with zlib.

* Solaris 11.2 ld: no compressed debug support yet.

* Test version of Solaris 12/11.2 ld: almost final now, command line
  option changed to -z compress-sections since the ELF gABI spec allows
  compresion of any non-allocable section.  I may follow this lead for
  gas/gld/gold, so the default for --compress-debug-sections (zlib-gnu)
  can remain unchanged, but the --compress-sections default would be
  zlib, following the gABI.

* GNU ld 2.23.2: I hadn't realized that gld can decompress on input, but
  always produces uncompressed output.

* GNU gold 2.23.2: can read and write compressed sections.

Ok for mainline now?

Thanks.

	Rainer


2013-04-10  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	* configure.ac (gcc_cv_as_compress_debug): Check for assembler
	compressed debug support.
	(gcc_cv_ld_compress_debug): Check for linker compressed debug
	support.
	* configure: Regenerate.
	* config.in: Regenerate.
	* common.opt (compressed_debug_sections): New enum.
	(gz, gz=): New options.
	* gcc.c (LINK_COMPRESS_DEBUG_SPEC, ASM_COMPRESS_DEBUG_SPEC):
	Define.
	(LINK_COMMAND_SPEC): Invoke LINK_COMPRESS_DEBUG_SPEC.
	(asm_options): Invoke ASM_COMPRESS_DEBUG_SPEC.
	* opts.c (common_handle_option): Handle OPT_gz, OPT_gz_.
	* doc/invoke.texi (Option Summary, Debugging Options): Add
	-gz[=type].
	(Debugging Options): Document -gz[=type].


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# HG changeset patch
# Parent a871a025093e293206f64a1d3b34ac7db53ee187
Enable --compress-debug-sections

diff --git a/gcc/common.opt b/gcc/common.opt
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -2407,6 +2407,28 @@ gxcoff+
 Common JoinedOrMissing Negative(gcoff)
 Generate debug information in extended XCOFF format
 
+Enum
+Name(compressed_debug_sections) Type(int)
+
+; Since -gz= is completely handled in specs, the values aren't used and we
+; assign arbitrary constants.
+EnumValue
+Enum(compressed_debug_sections) String(none) Value(0)
+
+EnumValue
+Enum(compressed_debug_sections) String(zlib) Value(1)
+
+EnumValue
+Enum(compressed_debug_sections) String(zlib-gnu) Value(2)
+
+gz
+Common Driver
+Generate compressed debug sections
+
+gz=
+Common Driver Joined Enum(compressed_debug_sections)
+-gz=<format>	Generate compressed debug sections in format <format>
+
 h
 Driver Joined Separate
 
diff --git a/gcc/configure.ac b/gcc/configure.ac
--- a/gcc/configure.ac
+++ b/gcc/configure.ac
@@ -4261,6 +4261,30 @@ if test x"$insn" != x; then
 [Define if your assembler supports the --debug-prefix-map option.])])
 fi
 
+gcc_GAS_CHECK_FEATURE([compressed debug sections],
+  gcc_cv_as_compress_debug,,,,
+  [# gas compiled without zlib cannot compress debug sections and warns
+   # about it, but still exits successfully.  So check for this, too.
+   if $gcc_cv_as --compress-debug-sections -o conftest.o conftest.s 2>&1 | grep -i warning > /dev/null
+   then
+     gcc_cv_as_compress_debug=0
+   elif $gcc_cv_as --compress-debug-sections -o conftest.o conftest.s > /dev/null 2>&1
+   then
+     gcc_cv_as_compress_debug=1
+     gcc_cv_as_compress_debug_option="--compress-debug-sections"
+     gcc_cv_as_no_compress_debug_option="--nocompress-debug-sections"
+   else
+     gcc_cv_as_compress_debug=0
+   # FIXME: Future gas versions will support ELF gABI style via
+   # --compress-debug-sections[=type].
+   fi])
+AC_DEFINE_UNQUOTED(HAVE_AS_COMPRESS_DEBUG, $gcc_cv_as_compress_debug,
+[Define to the level of your assembler's compressed debug section support.])
+AC_DEFINE_UNQUOTED(AS_COMPRESS_DEBUG_OPTION, "$gcc_cv_as_compress_debug_option",
+[Define to the assembler option to enable compressed debug sections.])
+AC_DEFINE_UNQUOTED(AS_NO_COMPRESS_DEBUG_OPTION, "$gcc_cv_as_no_compress_debug_option",
+[Define to the assembler option to disable compressed debug sections.])
+
 gcc_GAS_CHECK_FEATURE([.lcomm with alignment], gcc_cv_as_lcomm_with_alignment,
  ,,
 [.lcomm bar,4,16],,
@@ -4531,6 +4555,60 @@ if test x$gcc_cv_ld_eh_gc_sections_bug =
 fi
 AC_MSG_RESULT($gcc_cv_ld_eh_gc_sections_bug)
 
+AC_MSG_CHECKING(linker for compressed debug sections)
+# gold/gld support compressed debug sections since binutils 2.19/2.21
+if test $in_tree_ld = yes ; then
+  gcc_cv_ld_compress_debug=0
+  if test "$gcc_cv_gld_major_version" -eq 2 -a "$gcc_cv_gld_minor_version" -ge 19 -o "$gcc_cv_gld_major_version" -gt 2 \
+     && test $in_tree_ld_is_elf = yes && test $ld_is_gold = yes; then
+    gcc_cv_ld_compress_debug=2
+    gcc_cv_ld_compress_debug_option="--compress-debug-sections"
+  elif test "$gcc_cv_gld_major_version" -eq 2 -a "$gcc_cv_gld_minor_version" -ge 21 -o "$gcc_cv_gld_major_version" -gt 2 \
+     && test $in_tree_ld_is_elf = yes; then
+    gcc_cv_ld_compress_debug=1
+  fi
+elif echo "$ld_ver" | grep GNU > /dev/null; then
+  gcc_cv_ld_compress_debug=1
+  if test 0"$ld_date" -lt 20050308; then
+    if test -n "$ld_date"; then
+      # If there was date string, but was earlier than 2005-03-08, fail
+      gcc_cv_ld_compress_debug=0
+    elif test "$ld_vers_major" -lt 2; then
+      gcc_cv_ld_compress_debug=0
+    elif test "$ld_vers_major" -eq 2 -a "$ld_vers_minor" -lt 21; then
+      gcc_cv_ld_compress_debug=0
+    fi
+  fi
+  if test $ld_is_gold = yes; then
+    gcc_cv_ld_compress_debug=2
+    gcc_cv_ld_compress_debug_option="--compress-debug-sections"
+  fi
+else
+changequote(,)dnl
+  case "${target}" in
+    *-*-solaris2*)
+      # Introduced in Solaris 11.2.
+      if $gcc_cv_ld --help 2>&1 | grep -- '-z compress-sections' > /dev/null; then
+        gcc_cv_ld_compress_debug=3
+        gcc_cv_ld_compress_debug_option="-z compress-sections"
+      else
+        gcc_cv_ld_compress_debug=0
+      fi
+      ;;
+    *)
+      # Assume linkers other than GNU ld don't support compessed debug
+      # sections.
+      gcc_cv_ld_compress_debug=0
+      ;;
+  esac
+changequote([,])dnl
+fi
+AC_DEFINE_UNQUOTED(HAVE_LD_COMPRESS_DEBUG, $gcc_cv_ld_compress_debug,
+[Define to the level of your linker's compressed debug section support.])
+AC_DEFINE_UNQUOTED(LD_COMPRESS_DEBUG_OPTION, "$gcc_cv_ld_compress_debug_option",
+[Define to the linker option to enable compressed debug sections.])
+AC_MSG_RESULT($gcc_cv_ld_compress_debug)
+
 # --------
 # UNSORTED
 # --------
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -338,7 +338,7 @@ Objective-C and Objective-C++ Dialects}.
 -g  -g@var{level}  -gtoggle  -gcoff  -gdwarf-@var{version} @gol
 -ggdb  -grecord-gcc-switches  -gno-record-gcc-switches @gol
 -gstabs  -gstabs+  -gstrict-dwarf  -gno-strict-dwarf @gol
--gvms  -gxcoff  -gxcoff+ @gol
+-gvms  -gxcoff  -gxcoff+ -gz@r{[}=@var{type}@r{]} @gol
 -fno-merge-debug-strings -fno-dwarf2-cfi-asm @gol
 -fdebug-prefix-map=@var{old}=@var{new} @gol
 -femit-struct-debug-baseonly -femit-struct-debug-reduced @gol
@@ -5072,6 +5072,15 @@ DWARF extensions from later standard ver
 Allow using extensions of later DWARF standard version than selected with
 @option{-gdwarf-@var{version}}.
 
+@item -gz@r{[}=@var{type}@r{]}
+@opindex gz
+Produce compressed debug sections in DWARF format (if that is
+supported).  If @var{type} is not given, the default type depends on the
+capabilities of the assembler and linker used.  @var{type} may be one of
+@option{none} (don't compress debug sections), @option{zlib} (use zlib
+compression in ELF gABI format), or @option{zlib-gnu} (use zlib
+compression in traditional GNU format).
+
 @item -gvms
 @opindex gvms
 Produce debugging information in Alpha/VMS debug format (if that is
diff --git a/gcc/gcc.c b/gcc/gcc.c
--- a/gcc/gcc.c
+++ b/gcc/gcc.c
@@ -586,6 +586,32 @@ proper position among the other output f
 #define LIBTSAN_EARLY_SPEC ""
 #endif
 
+/* Linker options for compressed debug sections.  */
+#if HAVE_LD_COMPRESS_DEBUG == 0
+/* No linker support.  */
+#define LINK_COMPRESS_DEBUG_SPEC \
+	" %{gz*:%e-gz is not supported in this configuration}"
+#elif HAVE_LD_COMPRESS_DEBUG == 1
+/* GNU style on input, GNU ld options.  */
+#define LINK_COMPRESS_DEBUG_SPEC \
+	" %{gz:%e-gz is not supported in this configuration}" \
+	" %{gz=none:}" \
+	" %{gz=zlib:%e-gz=zlib is not supported in this configuration}" \
+	" %{gz=zlib-gnu:%e-gz=zlib-gnu is not supported in this configuration}"
+#elif HAVE_LD_COMPRESS_DEBUG == 2
+/* GNU style, GNU gold options.  */
+#define LINK_COMPRESS_DEBUG_SPEC \
+	" %{gz|gz=zlib-gnu:" LD_COMPRESS_DEBUG_OPTION "=zlib}" \
+	" %{gz=none:"        LD_COMPRESS_DEBUG_OPTION "=none}" \
+	" %{gz=zlib:%e-gz=zlib is not supported in this configuration}"
+#else
+/* ELF gABI style.  */
+#define LINK_COMPRESS_DEBUG_SPEC \
+	" %{gz|gz=zlib:"  LD_COMPRESS_DEBUG_OPTION "=zlib}" \
+	" %{gz=none:"	  LD_COMPRESS_DEBUG_OPTION "=none}" \
+	" %{gz=zlib-gnu:" LD_COMPRESS_DEBUG_OPTION "=zlib-gnu}"
+#endif
+
 /* config.h can define LIBGCC_SPEC to override how and when libgcc.a is
    included.  */
 #ifndef LIBGCC_SPEC
@@ -620,6 +646,25 @@ proper position among the other output f
 #define ASM_MAP ""
 #endif
 
+/* Assembler options for compressed debug sections.  */
+#if HAVE_AS_COMPRESS_DEBUG == 0
+/* No assembler support.  */
+#define ASM_COMPRESS_DEBUG_SPEC \
+	" %{gz*:%e-gz is not supported in this configuration}"
+#elif HAVE_AS_COMPRESS_DEBUG == 1
+/* GNU style, GNU as options.  */
+#define ASM_COMPRESS_DEBUG_SPEC \
+	" %{gz|gz=zlib-gnu:" AS_COMPRESS_DEBUG_OPTION "}" \
+	" %{gz=none:"        AS_NO_COMPRESS_DEBUG_OPTION "}" \
+	" %{gz=zlib:%e-gz=zlib is not supported in this configuration}"
+#else
+/* ELF gABI style.  */
+#define ASM_COMPRESS_DEBUG_SPEC \
+	" %{gz|gz=zlib:"  AS_COMPRESS_DEBUG_OPTION "=zlib}" \
+	" %{gz=none:"	  AS_COMPRESS_DEBUG_OPTION "=none}" \
+	" %{gz=zlib-gnu:" AS_COMPRESS_DEBUG_OPTION "=zlib-gnu}"
+#endif
+
 /* Define ASM_DEBUG_SPEC to be a spec suitable for translating '-g'
    to the assembler.  */
 #ifndef ASM_DEBUG_SPEC
@@ -737,8 +782,8 @@ proper position among the other output f
     LINK_PLUGIN_SPEC \
    "%{flto|flto=*:%<fcompare-debug*} \
     %{flto} %{flto=*} %l " LINK_PIE_SPEC \
-   "%{fuse-ld=*:-fuse-ld=%*}\
-    %X %{o*} %{e*} %{N} %{n} %{r}\
+   "%{fuse-ld=*:-fuse-ld=%*} " LINK_COMPRESS_DEBUG_SPEC \
+   "%X %{o*} %{e*} %{N} %{n} %{r}\
     %{s} %{t} %{u*} %{z} %{Z} %{!nostdlib:%{!nostartfiles:%S}}\
     %{static:} %{L*} %(mfwrap) %(link_libgcc) " SANITIZER_EARLY_SPEC " %o\
     %{fopenmp|ftree-parallelize-loops=*:%:include(libgomp.spec)%(link_gomp)}\
@@ -865,6 +910,7 @@ static const char *asm_options =
    to the assembler equivalents.  */
 "%{v} %{w:-W} %{I*} "
 #endif
+ASM_COMPRESS_DEBUG_SPEC
 "%a %Y %{c:%W{o*}%{!o*:-o %w%b%O}}%{!c:-o %d%w%u%O}";
 
 static const char *invoke_as =
diff --git a/gcc/opts.c b/gcc/opts.c
--- a/gcc/opts.c
+++ b/gcc/opts.c
@@ -1750,6 +1750,11 @@ common_handle_option (struct gcc_options
 		       loc);
       break;
 
+    case OPT_gz:
+    case OPT_gz_:
+      /* Handled completely via specs.  */
+      break;
+
     case OPT_pedantic_errors:
       dc->pedantic_errors = 1;
       control_warning_option (OPT_Wpedantic, DK_ERROR, value,

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-- 
-----------------------------------------------------------------------------
Rainer Orth, Center for Biotechnology, Bielefeld University

Re: [build, driver] RFC: Support compressed debug sections

[Joseph S. Myers]

On Tue, 30 Apr 2013, Rainer Orth wrote:

> 	* gcc.c (LINK_COMPRESS_DEBUG_SPEC, ASM_COMPRESS_DEBUG_SPEC):
> 	Define.
> 	(LINK_COMMAND_SPEC): Invoke LINK_COMPRESS_DEBUG_SPEC.
> 	(asm_options): Invoke ASM_COMPRESS_DEBUG_SPEC.

Note that there are separate copies of LINK_COMMAND_SPEC in darwin.h and 
i386/djgpp.h, which maybe should include the new spec.

It's not clear to me from the documentation added by this patch whether 
users are meant to specify their -gz options when compiling, when linking, 
or both - and whether there might be cases when such an option is accepted 
for one of compiling and linking but not the other (which would be 
especially confusing).

-- 
Joseph S. Myers
joseph@codesourcery.com

Re: [build, driver] RFC: Support compressed debug sections

[Rainer Orth]

[-- Attachment #1: Type: text/plain, Size: 1364 bytes --]

"Joseph S. Myers" <joseph@codesourcery.com> writes:

> On Tue, 30 Apr 2013, Rainer Orth wrote:
>
>> 	* gcc.c (LINK_COMPRESS_DEBUG_SPEC, ASM_COMPRESS_DEBUG_SPEC):
>> 	Define.
>> 	(LINK_COMMAND_SPEC): Invoke LINK_COMPRESS_DEBUG_SPEC.
>> 	(asm_options): Invoke ASM_COMPRESS_DEBUG_SPEC.
>
> Note that there are separate copies of LINK_COMMAND_SPEC in darwin.h and 
> i386/djgpp.h, which maybe should include the new spec.

I hadn't thought about that.  Here's what I found:

* Darwin is Mach-O, but current gas supports DWARF-in-Mach-O.
  Unfortunately, current gcc mainline only supports Apple as:
  i386/darwin.h hardcodes as-only options in ASM_SPEC, which causes gas
  to barf.  If you manually invoke gas on gcc -gdwarf output, you get
  compressed debug sections, though objdump cannot handle them.

* DJGPP is COFF, but again gas seems to support DWARF.  Unfortunately,
  current gcc mainline doesn't even build:

gcc/config/i386/i386.c: In function 'void ix86_code_end()':
gcc/config/i386/i386.c:8667: error: 'ASM_DECLARE_FUNCTION_NAME' was not declared in this scope

  I didn't look further from here.

Anyway, I tried a i386-pc-solaris2.11 x i686-pc-darwin build with the
following patch to check it doesn't break the build:

	* config/darwin.h (LINK_COMMAND_SPEC_A): Invoke
	LINK_COMPRESS_DEBUG_SPEC.
	* config/i386/djgpp.h (LINK_COMMAND_SPEC): Likewise.


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diff --git a/gcc/config/darwin.h b/gcc/config/darwin.h
--- a/gcc/config/darwin.h
+++ b/gcc/config/darwin.h
@@ -171,7 +171,8 @@ extern GTY(()) int darwin_ms_struct;
     LINK_PLUGIN_SPEC \
     "%{flto*:%<fcompare-debug*} \
     %{flto*} \
-    %l %X %{s} %{t} %{Z} %{u*} \
+    %l " LINK_COMPRESS_DEBUG_SPEC \
+   "%X %{s} %{t} %{Z} %{u*} \
     %{e*} %{r} \
     %{o*}%{!o:-o a.out} \
     %{!nostdlib:%{!nostartfiles:%S}} \
diff --git a/gcc/config/i386/djgpp.h b/gcc/config/i386/djgpp.h
--- a/gcc/config/i386/djgpp.h
+++ b/gcc/config/i386/djgpp.h
@@ -80,7 +80,8 @@ along with GCC; see the file COPYING3.  
 #undef LINK_COMMAND_SPEC
 #define LINK_COMMAND_SPEC \
 "%{!fsyntax-only: \
-%{!c:%{!M:%{!MM:%{!E:%{!S:%(linker) %l %X %{o*} %{e*} %{N} %{n} \
+%{!c:%{!M:%{!MM:%{!E:%{!S:%(linker) %l " LINK_COMPRESS_DEBUG_SPEC \
+"%X %{o*} %{e*} %{N} %{n} \
 \t%{r} %{s} %{t} %{u*} %{z} %{Z}\
 \t%{!nostdlib:%{!nostartfiles:%S}}\
 \t%{static:} %{L*} %D %o\

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Especially darwin.h LINK_COMMAND_SPEC_A is a total mess: it's a copy of
gcc.c LINK_COMMAND_SPEC with various changes not carried forward and
other parts done in a slightly different syntax for no apparent reason.
I'm pretty sure the two could be merged to avoid problems from
duplication in the future, but I'll leave that to the Darwin
maintainers.

I can include the snippet above for symmetry, if only to reject -gz as
on ELF targets without the toolchain support, if you prefer.

> It's not clear to me from the documentation added by this patch whether 
> users are meant to specify their -gz options when compiling, when linking, 
> or both - and whether there might be cases when such an option is accepted 
> for one of compiling and linking but not the other (which would be 
> especially confusing).

The goal is to have -gz work for both compilation and linking, but
unfortunately, the current situation very much depends on both the
toolchain used and your intentions.  The following matrix shows read and
write support in the GNU and Solaris toolchains.  For the latter, full
support for zlib and zlib-gnu formats is being worked on, with ld
already there.

		GNU			Solaris
		gas  gld  gold	gdb	as   ld   dbx
		w    r w  r w	r	w    r w  r

      none	x    x x  x x	x	x    x x  x
      zlib-gnu	x    x 	  x x	x	     x x
      zlib	     	    		     x x

I plan to add zlib support first to gas and gdb, eventually to gld
(which also means adding support for compression on output, though I had
a very hard time finding my way through bfd and gld in the past), but
will rely on Cary Coutant and/or Ian, who were involved in the zlib/ELF
gABI format design, to handle gold.

Right now, the gas/gold combination supports -gz just fine (producing
the zlib-gnu format), while gas/gld only support -gz in the assemble
step.  I know this is highly undesirable, but whether or not it's
acceptable depends on your goals:

* If you mean to trade compilation/assembly speed for disk usage, -gz
  for compilation only is ok.

* If your primary goal is space savings for executables and shared
  objects while still allowing debugability, you need to use gold for
  -gz at link time to work.

	Rainer

-- 
-----------------------------------------------------------------------------
Rainer Orth, Center for Biotechnology, Bielefeld University

Re: [build, driver] RFC: Support compressed debug sections

[Joseph S. Myers]

I still have no idea from your answer how a user is meant to know whether 
to use the option when compiling, linking or both, which is what needs to 
be clear from invoke.texi.

What does it mean for the option to be supported for compiling but not 
linking?  What in that case will the linker do with compressed debug 
sections on input?  Combine them in some way, good or bad?  Uncompress 
them?

Likewise, for it to be supported for linking but not compiling?  Will the 
linker then compress the uncompressed sections it receives on input?

I think it would be better if the option semantics are more like "if you 
pass the same option when both compiling and linking, the linked output 
will have the sections appropriately compressed as specified by the 
option, whether or not the individual .o files do" - and if this can't be 
supported with the tools being used, don't allow the option.

-- 
Joseph S. Myers
joseph@codesourcery.com

Re: [build, driver] RFC: Support compressed debug sections

[Rainer Orth]

Hi Joseph,

> I still have no idea from your answer how a user is meant to know whether 
> to use the option when compiling, linking or both, which is what needs to 
> be clear from invoke.texi.
>
> What does it mean for the option to be supported for compiling but not 
> linking?  What in that case will the linker do with compressed debug 
> sections on input?  Combine them in some way, good or bad?  Uncompress 
> them?

a linker that doesn't understand compressed debug sections will probably
combine them in a useless way.  If, like gld, it can read but not write
them, they will be written in uncompressed form.

> Likewise, for it to be supported for linking but not compiling?  Will the 
> linker then compress the uncompressed sections it receives on input?

Yes, that will work in all cases.

> I think it would be better if the option semantics are more like "if you 
> pass the same option when both compiling and linking, the linked output 
> will have the sections appropriately compressed as specified by the 
> option, whether or not the individual .o files do" - and if this can't be 
> supported with the tools being used, don't allow the option.

That's certainly an option, as in the following table (taking the
zlib-gnu format as an example, but omitting hypothetical linkers that
can write but not read compressed debug sections):

      assembler		linker		action			example
      w			r	w

      -			-	-	reject			as/ld
      -			x	-	reject, useless		as/gld
      -			x	x	ok, warn about no-op as -gz?	as/gold
      x			-	-	reject, harmful	   	gas/ld
      x			x	-	reject, useless		gas/gld
      x			x	x	ok			gas/gold

The only problem I see is that for an assembler not supporting
compression -gz would be a silent no-op.  I'd rather warn about this
instead, but still accept it so you can both compile and link with -gz.

	Rainer

-- 
-----------------------------------------------------------------------------
Rainer Orth, Center for Biotechnology, Bielefeld University

Re: [build, driver] RFC: Support compressed debug sections

[Rainer Orth]

[-- Attachment #1: Type: text/plain, Size: 2781 bytes --]

"Joseph S. Myers" <joseph@codesourcery.com> writes:

[Sorry for dropping the ball on this for so long.]

> I still have no idea from your answer how a user is meant to know whether 
> to use the option when compiling, linking or both, which is what needs to 
> be clear from invoke.texi.
>
> What does it mean for the option to be supported for compiling but not 
> linking?  What in that case will the linker do with compressed debug 
> sections on input?  Combine them in some way, good or bad?  Uncompress 
> them?
>
> Likewise, for it to be supported for linking but not compiling?  Will the 
> linker then compress the uncompressed sections it receives on input?
>
> I think it would be better if the option semantics are more like "if you 
> pass the same option when both compiling and linking, the linked output 
> will have the sections appropriately compressed as specified by the 
> option, whether or not the individual .o files do" - and if this can't be 
> supported with the tools being used, don't allow the option.

Ok, makes sense: although it may lose some of the capabilities of the
toolchain (like gas/gld, where gas can write compressed debug, gld can
read, but not write it), the user experience is certainly better.  I
thought about warning for an assembler not supporting compressed debug
when -gz is passed, but that would only produce noise.

So here's the revised patch.  Tested on

* i386-pc-solaris2.10 with gas/ld: gas could write but ld cannot read
  compressed debug, so reject all -gz options.

* i386-pc-solaris2.11 with gas/ld: gas can write zlib-gnu format, ld can
  read and write all of them

* x86_64-unknown-linux-gnu with gas/gold: gas can write, gold can read
  and write zlib-gnu format

In every case, -gz and -gz=<format> behaved as expected as checked by
inspecting the assembler and linker invocations and the resulting object
files and executables.

Ok for mainline now?

Thanks.
        Rainer


2013-04-10  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	gcc:
	* configure.ac (gcc_cv_as_compress_debug): Check for assembler
	compressed debug support.
	(gcc_cv_ld_compress_debug): Check for linker compressed debug
	support.
	* configure: Regenerate.
	* config.in: Regenerate.
	* common.opt (compressed_debug_sections): New enum.
	(gz, gz=): New options.
	* gcc.c (LINK_COMPRESS_DEBUG_SPEC, ASM_COMPRESS_DEBUG_SPEC):
	Define.
	(LINK_COMMAND_SPEC): Invoke LINK_COMPRESS_DEBUG_SPEC.
	(asm_options): Invoke ASM_COMPRESS_DEBUG_SPEC.
	* config/darwin.h (LINK_COMMAND_SPEC_A): Invoke
	LINK_COMPRESS_DEBUG_SPEC.
	* config/i386/djgpp.h (LINK_COMMAND_SPEC): Likewise.
	* opts.c (common_handle_option): Handle OPT_gz, OPT_gz_.
	* doc/invoke.texi (Option Summary, Debugging Options): Add
	-gz[=type].
	(Debugging Options): Document -gz[=type].


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[-- Attachment #2: compress-debug-sections.patch --]
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# HG changeset patch
# Parent 461334df01269c96bf9f041380cfc901c395307d
Enable --compress-debug-sections

diff --git a/gcc/common.opt b/gcc/common.opt
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -2518,6 +2518,28 @@ gxcoff+
 Common JoinedOrMissing Negative(gcoff)
 Generate debug information in extended XCOFF format
 
+Enum
+Name(compressed_debug_sections) Type(int)
+
+; Since -gz= is completely handled in specs, the values aren't used and we
+; assign arbitrary constants.
+EnumValue
+Enum(compressed_debug_sections) String(none) Value(0)
+
+EnumValue
+Enum(compressed_debug_sections) String(zlib) Value(1)
+
+EnumValue
+Enum(compressed_debug_sections) String(zlib-gnu) Value(2)
+
+gz
+Common Driver
+Generate compressed debug sections
+
+gz=
+Common Driver Joined Enum(compressed_debug_sections)
+-gz=<format>	Generate compressed debug sections in format <format>
+
 h
 Driver Joined Separate
 
diff --git a/gcc/config/darwin.h b/gcc/config/darwin.h
--- a/gcc/config/darwin.h
+++ b/gcc/config/darwin.h
@@ -171,7 +171,8 @@ extern GTY(()) int darwin_ms_struct;
     LINK_PLUGIN_SPEC \
     "%{flto*:%<fcompare-debug*} \
     %{flto*} \
-    %l %X %{s} %{t} %{Z} %{u*} \
+    %l " LINK_COMPRESS_DEBUG_SPEC \
+   "%X %{s} %{t} %{Z} %{u*} \
     %{e*} %{r} \
     %{o*}%{!o:-o a.out} \
     %{!nostdlib:%{!nostartfiles:%S}} \
diff --git a/gcc/config/i386/djgpp.h b/gcc/config/i386/djgpp.h
--- a/gcc/config/i386/djgpp.h
+++ b/gcc/config/i386/djgpp.h
@@ -80,7 +80,8 @@ along with GCC; see the file COPYING3.  
 #undef LINK_COMMAND_SPEC
 #define LINK_COMMAND_SPEC \
 "%{!fsyntax-only: \
-%{!c:%{!M:%{!MM:%{!E:%{!S:%(linker) %l %X %{o*} %{e*} %{N} %{n} \
+%{!c:%{!M:%{!MM:%{!E:%{!S:%(linker) %l " LINK_COMPRESS_DEBUG_SPEC \
+"%X %{o*} %{e*} %{N} %{n} \
 \t%{r} %{s} %{t} %{u*} %{z} %{Z}\
 \t%{!nostdlib:%{!nostartfiles:%S}}\
 \t%{static:} %{L*} %D %o\
diff --git a/gcc/configure.ac b/gcc/configure.ac
--- a/gcc/configure.ac
+++ b/gcc/configure.ac
@@ -4370,6 +4370,30 @@ if test x"$insn" != x; then
 [Define if your assembler supports the --debug-prefix-map option.])])
 fi
 
+gcc_GAS_CHECK_FEATURE([compressed debug sections],
+  gcc_cv_as_compress_debug,,[--compress-debug-sections],,
+  [# gas compiled without zlib cannot compress debug sections and warns
+   # about it, but still exits successfully.  So check for this, too.
+   if $gcc_cv_as --compress-debug-sections -o conftest.o conftest.s 2>&1 | grep -i warning > /dev/null
+   then
+     gcc_cv_as_compress_debug=0
+   elif $gcc_cv_as --compress-debug-sections -o conftest.o conftest.s > /dev/null 2>&1
+   then
+     gcc_cv_as_compress_debug=1
+     gcc_cv_as_compress_debug_option="--compress-debug-sections"
+     gcc_cv_as_no_compress_debug_option="--nocompress-debug-sections"
+   else
+     gcc_cv_as_compress_debug=0
+   # FIXME: Future gas versions will support ELF gABI style via
+   # --compress-debug-sections[=type].
+   fi])
+AC_DEFINE_UNQUOTED(HAVE_AS_COMPRESS_DEBUG, $gcc_cv_as_compress_debug,
+[Define to the level of your assembler's compressed debug section support.])
+AC_DEFINE_UNQUOTED(AS_COMPRESS_DEBUG_OPTION, "$gcc_cv_as_compress_debug_option",
+[Define to the assembler option to enable compressed debug sections.])
+AC_DEFINE_UNQUOTED(AS_NO_COMPRESS_DEBUG_OPTION, "$gcc_cv_as_no_compress_debug_option",
+[Define to the assembler option to disable compressed debug sections.])
+
 gcc_GAS_CHECK_FEATURE([.lcomm with alignment], gcc_cv_as_lcomm_with_alignment,
  ,,
 [.lcomm bar,4,16],,
@@ -4676,6 +4700,60 @@ if test x$gcc_cv_ld_eh_gc_sections_bug =
 fi
 AC_MSG_RESULT($gcc_cv_ld_eh_gc_sections_bug)
 
+AC_MSG_CHECKING(linker for compressed debug sections)
+# gold/gld support compressed debug sections since binutils 2.19/2.21
+if test $in_tree_ld = yes ; then
+  gcc_cv_ld_compress_debug=0
+  if test "$gcc_cv_gld_major_version" -eq 2 -a "$gcc_cv_gld_minor_version" -ge 19 -o "$gcc_cv_gld_major_version" -gt 2 \
+     && test $in_tree_ld_is_elf = yes && test $ld_is_gold = yes; then
+    gcc_cv_ld_compress_debug=2
+    gcc_cv_ld_compress_debug_option="--compress-debug-sections"
+  elif test "$gcc_cv_gld_major_version" -eq 2 -a "$gcc_cv_gld_minor_version" -ge 21 -o "$gcc_cv_gld_major_version" -gt 2 \
+     && test $in_tree_ld_is_elf = yes; then
+    gcc_cv_ld_compress_debug=1
+  fi
+elif echo "$ld_ver" | grep GNU > /dev/null; then
+  gcc_cv_ld_compress_debug=1
+  if test 0"$ld_date" -lt 20050308; then
+    if test -n "$ld_date"; then
+      # If there was date string, but was earlier than 2005-03-08, fail
+      gcc_cv_ld_compress_debug=0
+    elif test "$ld_vers_major" -lt 2; then
+      gcc_cv_ld_compress_debug=0
+    elif test "$ld_vers_major" -eq 2 -a "$ld_vers_minor" -lt 21; then
+      gcc_cv_ld_compress_debug=0
+    fi
+  fi
+  if test $ld_is_gold = yes; then
+    gcc_cv_ld_compress_debug=2
+    gcc_cv_ld_compress_debug_option="--compress-debug-sections"
+  fi
+else
+changequote(,)dnl
+  case "${target}" in
+    *-*-solaris2*)
+      # Introduced in Solaris 11.2.
+      if $gcc_cv_ld --help 2>&1 | grep -- '-z compress-sections' > /dev/null; then
+        gcc_cv_ld_compress_debug=3
+        gcc_cv_ld_compress_debug_option="-z compress-sections"
+      else
+        gcc_cv_ld_compress_debug=0
+      fi
+      ;;
+    *)
+      # Assume linkers other than GNU ld don't support compessed debug
+      # sections.
+      gcc_cv_ld_compress_debug=0
+      ;;
+  esac
+changequote([,])dnl
+fi
+AC_DEFINE_UNQUOTED(HAVE_LD_COMPRESS_DEBUG, $gcc_cv_ld_compress_debug,
+[Define to the level of your linker's compressed debug section support.])
+AC_DEFINE_UNQUOTED(LD_COMPRESS_DEBUG_OPTION, "$gcc_cv_ld_compress_debug_option",
+[Define to the linker option to enable compressed debug sections.])
+AC_MSG_RESULT($gcc_cv_ld_compress_debug)
+
 # --------
 # UNSORTED
 # --------
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -344,7 +344,7 @@ Objective-C and Objective-C++ Dialects}.
 -g  -g@var{level}  -gtoggle  -gcoff  -gdwarf-@var{version} @gol
 -ggdb  -grecord-gcc-switches  -gno-record-gcc-switches @gol
 -gstabs  -gstabs+  -gstrict-dwarf  -gno-strict-dwarf @gol
--gvms  -gxcoff  -gxcoff+ @gol
+-gvms  -gxcoff  -gxcoff+ -gz@r{[}=@var{type}@r{]} @gol
 -fno-merge-debug-strings -fno-dwarf2-cfi-asm @gol
 -fdebug-prefix-map=@var{old}=@var{new} @gol
 -femit-struct-debug-baseonly -femit-struct-debug-reduced @gol
@@ -5274,6 +5274,18 @@ DWARF extensions from later standard ver
 Allow using extensions of later DWARF standard version than selected with
 @option{-gdwarf-@var{version}}.
 
+@item -gz@r{[}=@var{type}@r{]}
+@opindex gz
+Produce compressed debug sections in DWARF format, if that is supported.
+If @var{type} is not given, the default type depends on the capabilities
+of the assembler and linker used.  If the linker doesn't support writing
+compressed debug sections, the option is rejected.  Otherwise, if the
+assembler doesn't support them, @option{-gz} is silently ignored when
+producing object files.  @var{type} may be one of @option{none} (don't
+compress debug sections), @option{zlib} (use zlib compression in ELF
+gABI format), or @option{zlib-gnu} (use zlib compression in traditional
+GNU format).
+
 @item -gvms
 @opindex gvms
 Produce debugging information in Alpha/VMS debug format (if that is
diff --git a/gcc/gcc.c b/gcc/gcc.c
--- a/gcc/gcc.c
+++ b/gcc/gcc.c
@@ -597,6 +597,31 @@ proper position among the other output f
 #endif
 #endif
 
+/* Linker options for compressed debug sections.  */
+#if HAVE_LD_COMPRESS_DEBUG == 0
+/* No linker support.  */
+#define LINK_COMPRESS_DEBUG_SPEC \
+	" %{gz*:%e-gz is not supported in this configuration} "
+#elif HAVE_LD_COMPRESS_DEBUG == 1
+/* GNU style on input, GNU ld options.  Reject, not useful.  */
+#define LINK_COMPRESS_DEBUG_SPEC \
+	" %{gz*:%e-gz is not supported in this configuration} "
+#elif HAVE_LD_COMPRESS_DEBUG == 2
+/* GNU style, GNU gold options.  */
+#define LINK_COMPRESS_DEBUG_SPEC \
+	" %{gz|gz=zlib-gnu:" LD_COMPRESS_DEBUG_OPTION "=zlib}" \
+	" %{gz=none:"        LD_COMPRESS_DEBUG_OPTION "=none}" \
+	" %{gz=zlib:%e-gz=zlib is not supported in this configuration} "
+#elif HAVE_LD_COMPRESS_DEBUG == 3
+/* ELF gABI style.  */
+#define LINK_COMPRESS_DEBUG_SPEC \
+	" %{gz|gz=zlib:"  LD_COMPRESS_DEBUG_OPTION "=zlib}" \
+	" %{gz=none:"	  LD_COMPRESS_DEBUG_OPTION "=none}" \
+	" %{gz=zlib-gnu:" LD_COMPRESS_DEBUG_OPTION "=zlib-gnu} "
+#else
+#error Unknown value for HAVE_LD_COMPRESS_DEBUG.
+#endif
+
 /* config.h can define LIBGCC_SPEC to override how and when libgcc.a is
    included.  */
 #ifndef LIBGCC_SPEC
@@ -631,6 +656,33 @@ proper position among the other output f
 #define ASM_MAP ""
 #endif
 
+/* Assembler options for compressed debug sections.  */
+#if HAVE_LD_COMPRESS_DEBUG < 2
+/* Reject if the linker cannot write compressed debug sections.  */
+#define ASM_COMPRESS_DEBUG_SPEC \
+	" %{gz*:%e-gz is not supported in this configuration} "
+#else /* HAVE_LD_COMPRESS_DEBUG >= 2 */
+#if HAVE_AS_COMPRESS_DEBUG == 0
+/* No assembler support.  Ignore silently.  */
+#define ASM_COMPRESS_DEBUG_SPEC \
+	" %{gz*:} "
+#elif HAVE_AS_COMPRESS_DEBUG == 1
+/* GNU style, GNU as options.  */
+#define ASM_COMPRESS_DEBUG_SPEC \
+	" %{gz|gz=zlib-gnu:" AS_COMPRESS_DEBUG_OPTION "}" \
+	" %{gz=none:"        AS_NO_COMPRESS_DEBUG_OPTION "}" \
+	" %{gz=zlib:%e-gz=zlib is not supported in this configuration} "
+#elif HAVE_AS_COMPRESS_DEBUG == 2
+/* ELF gABI style.  */
+#define ASM_COMPRESS_DEBUG_SPEC \
+	" %{gz|gz=zlib:"  AS_COMPRESS_DEBUG_OPTION "=zlib}" \
+	" %{gz=none:"	  AS_COMPRESS_DEBUG_OPTION "=none}" \
+	" %{gz=zlib-gnu:" AS_COMPRESS_DEBUG_OPTION "=zlib-gnu} "
+#else
+#error Unknown value for HAVE_AS_COMPRESS_DEBUG.
+#endif
+#endif /* HAVE_LD_COMPRESS_DEBUG >= 2 */
+
 /* Define ASM_DEBUG_SPEC to be a spec suitable for translating '-g'
    to the assembler.  */
 #ifndef ASM_DEBUG_SPEC
@@ -761,8 +813,8 @@ proper position among the other output f
     LINK_PLUGIN_SPEC \
    "%{flto|flto=*:%<fcompare-debug*} \
     %{flto} %{flto=*} %l " LINK_PIE_SPEC \
-   "%{fuse-ld=*:-fuse-ld=%*}\
-    %X %{o*} %{e*} %{N} %{n} %{r}\
+   "%{fuse-ld=*:-fuse-ld=%*} " LINK_COMPRESS_DEBUG_SPEC \
+   "%X %{o*} %{e*} %{N} %{n} %{r}\
     %{s} %{t} %{u*} %{z} %{Z} %{!nostdlib:%{!nostartfiles:%S}} " VTABLE_VERIFICATION_SPEC " \
     %{static:} %{L*} %(mfwrap) %(link_libgcc) " SANITIZER_EARLY_SPEC " %o\
     %{fopenmp|ftree-parallelize-loops=*:%:include(libgomp.spec)%(link_gomp)}\
@@ -885,6 +937,7 @@ static const char *asm_options =
    to the assembler equivalents.  */
 "%{v} %{w:-W} %{I*} "
 #endif
+ASM_COMPRESS_DEBUG_SPEC
 "%a %Y %{c:%W{o*}%{!o*:-o %w%b%O}}%{!c:-o %d%w%u%O}";
 
 static const char *invoke_as =
diff --git a/gcc/opts.c b/gcc/opts.c
--- a/gcc/opts.c
+++ b/gcc/opts.c
@@ -1867,6 +1867,11 @@ common_handle_option (struct gcc_options
 		       loc);
       break;
 
+    case OPT_gz:
+    case OPT_gz_:
+      /* Handled completely via specs.  */
+      break;
+
     case OPT_pedantic_errors:
       dc->pedantic_errors = 1;
       control_warning_option (OPT_Wpedantic, DK_ERROR, value,

[-- Attachment #3: Type: text/plain, Size: 143 bytes --]


-- 
-----------------------------------------------------------------------------
Rainer Orth, Center for Biotechnology, Bielefeld University

Re: [build, driver] RFC: Support compressed debug sections

[Joseph S. Myers]

On Thu, 22 May 2014, Rainer Orth wrote:

> 	* common.opt (compressed_debug_sections): New enum.
> 	(gz, gz=): New options.

> 	* opts.c (common_handle_option): Handle OPT_gz, OPT_gz_.

Given that the options are completely handled via specs, why can't they 
just be Driver options (without Common) and so not mentioned in 
common_handle_option?

-- 
Joseph S. Myers
joseph@codesourcery.com

Re: [build, driver] RFC: Support compressed debug sections

[Rainer Orth]

"Joseph S. Myers" <joseph@codesourcery.com> writes:

> On Thu, 22 May 2014, Rainer Orth wrote:
>
>> 	* common.opt (compressed_debug_sections): New enum.
>> 	(gz, gz=): New options.
>
>> 	* opts.c (common_handle_option): Handle OPT_gz, OPT_gz_.
>
> Given that the options are completely handled via specs, why can't they 
> just be Driver options (without Common) and so not mentioned in 
> common_handle_option?

If I do this, -gz still gets passed to e.g. cc1, which errors out like
this:

cc1: error: unrecognised debug output level "z"

It seems my way of handling this is clearer than doing this in opts.c
(set_debug_level).

	Rainer

-- 
-----------------------------------------------------------------------------
Rainer Orth, Center for Biotechnology, Bielefeld University

Re: [build, driver] RFC: Support compressed debug sections

[Joseph S. Myers]

On Thu, 22 May 2014, Rainer Orth wrote:

> "Joseph S. Myers" <joseph@codesourcery.com> writes:
> 
> > On Thu, 22 May 2014, Rainer Orth wrote:
> >
> >> 	* common.opt (compressed_debug_sections): New enum.
> >> 	(gz, gz=): New options.
> >
> >> 	* opts.c (common_handle_option): Handle OPT_gz, OPT_gz_.
> >
> > Given that the options are completely handled via specs, why can't they 
> > just be Driver options (without Common) and so not mentioned in 
> > common_handle_option?
> 
> If I do this, -gz still gets passed to e.g. cc1, which errors out like
> this:
> 
> cc1: error: unrecognised debug output level "z"
> 
> It seems my way of handling this is clearer than doing this in opts.c
> (set_debug_level).

Thanks for the explanation.  The driver changes are OK.

-- 
Joseph S. Myers
joseph@codesourcery.com

Re: [build, driver] RFC: Support compressed debug sections

[Rainer Orth]

"Joseph S. Myers" <joseph@codesourcery.com> writes:

> On Thu, 22 May 2014, Rainer Orth wrote:
>
>> "Joseph S. Myers" <joseph@codesourcery.com> writes:
>> 
>> > On Thu, 22 May 2014, Rainer Orth wrote:
>> >
>> >> 	* common.opt (compressed_debug_sections): New enum.
>> >> 	(gz, gz=): New options.
>> >
>> >> 	* opts.c (common_handle_option): Handle OPT_gz, OPT_gz_.
>> >
>> > Given that the options are completely handled via specs, why can't they 
>> > just be Driver options (without Common) and so not mentioned in 
>> > common_handle_option?
>> 
>> If I do this, -gz still gets passed to e.g. cc1, which errors out like
>> this:
>> 
>> cc1: error: unrecognised debug output level "z"
>> 
>> It seems my way of handling this is clearer than doing this in opts.c
>> (set_debug_level).
>
> Thanks for the explanation.  The driver changes are OK.

Thanks.  I still need approval for the doc and build parts, as well as
the Darwin and DJGPP changes.  For the latter two, I've included the
patch in a x86_64-apple-darwin11.4.2 build, verifying that -gz is
rejected as expected (no idea if the are any working gas and gold ports
that would support the option).  For DJGPP, I've tried a
i386-pc-solaris2.11 x i586-pc-msdosdjgpp cross.  While the specs
additions look correct, trying to compile even the most trivial program
SEGVs:

ro@snoopy 319 > ./xgcc -B./ -o hello hello.c
<built-in>: internal compiler error: Segmentation Fault
0x87549df crash_signal
        /vol/gcc/src/hg/trunk/local/gcc/toplev.c:337
0x82b8270 contains_struct_check
        /vol/gcc/src/hg/trunk/local/gcc/tree.h:2841
0x82b8270 c_common_nodes_and_builtins()
        /vol/gcc/src/hg/trunk/local/gcc/c-family/c-common.c:5619
0x82437be c_init_decl_processing()
        /vol/gcc/src/hg/trunk/local/gcc/c/c-decl.c:3567
0x827fe1a c_objc_common_init()
        /vol/gcc/src/hg/trunk/local/gcc/c/c-objc-common.c:63
0x8756333 lang_dependent_init
        /vol/gcc/src/hg/trunk/local/gcc/toplev.c:1712
0x8756333 do_compile
        /vol/gcc/src/hg/trunk/local/gcc/toplev.c:1901

	Rainer

-- 
-----------------------------------------------------------------------------
Rainer Orth, Center for Biotechnology, Bielefeld University

Re: [build, driver] RFC: Support compressed debug sections

[DJ Delorie]

> Thanks.  I still need approval for the doc and build parts, as well
> as the Darwin and DJGPP changes.  For the latter two, I've included
> the

I'll approve the DJGPP change, despite the segv.  I suspect it's
unrelated.

Re: [build, driver] RFC: Support compressed debug sections

[Rainer Orth]

Rainer Orth <ro@CeBiTec.Uni-Bielefeld.DE> writes:

> "Joseph S. Myers" <joseph@codesourcery.com> writes:
[...]
>> Thanks for the explanation.  The driver changes are OK.
>
> Thanks.  I still need approval for the doc and build parts, as well as
> the Darwin and DJGPP changes.  For the latter two, I've included the
> patch in a x86_64-apple-darwin11.4.2 build, verifying that -gz is
> rejected as expected (no idea if the are any working gas and gold ports
> that would support the option).  For DJGPP, I've tried a
> i386-pc-solaris2.11 x i586-pc-msdosdjgpp cross.  While the specs
> additions look correct, trying to compile even the most trivial program
> SEGVs:
[...]

It's been another week, and I still need approval for the build, doc,
and Darwin changes:

	https://gcc.gnu.org/ml/gcc-patches/2014-05/msg01860.html

Thanks.
        Rainer

-- 
-----------------------------------------------------------------------------
Rainer Orth, Center for Biotechnology, Bielefeld University

Re: [build, driver] RFC: Support compressed debug sections

[Mike Stump]

On Jun 3, 2014, at 3:40 AM, Rainer Orth <ro@CeBiTec.Uni-Bielefeld.DE> wrote:
> It's been another week, and I still need approval for the build, doc,
> and Darwin changes:

So, the darwin bits look trivial enough, if the entire scheme is what people want to do.  My question would be, why do we want an option for this?  If the scheme works, why not just turn it on unconditionally?  If it doesn’t work, why add it?  If it isn’t good, why add it?  If it is good, why not do it?

If it is just to reach compatibility with the debugger, then I’d rather either just mandate a certain debugger or autoconf for what the current debugger supports.  As of late people seem to just break the debugging experience with non-updated gdbs and assume that a newer gdb is used.

Re: [build, driver] RFC: Support compressed debug sections

[Gerald Pfeifer]

On Tue, 3 Jun 2014, Rainer Orth wrote:
> It's been another week, and I still need approval for the build, doc,
> and Darwin changes:
> 
> 	https://gcc.gnu.org/ml/gcc-patches/2014-05/msg01860.html

On the doc side, things are fine.

Just a suggestion or two:

+Produce compressed debug sections in DWARF format, if that is supported.

Supported by what?

"doesn't" -> "does not", especially given the emphasis we want to make
here.

And could the "If the linker doesn't support writing compressed debug 
sections, the option is rejected.  Otherwise, if the assembler doesn't 
support them, @option{-gz} is silently ignored when producing object 
files." be moved to the very end, or is this only applicable to the
case where no type has been specified?

Gerald

Re: [build, driver] RFC: Support compressed debug sections

[Rainer Orth]

Mike Stump <mikestump@comcast.net> writes:

> On Jun 3, 2014, at 3:40 AM, Rainer Orth <ro@CeBiTec.Uni-Bielefeld.DE> wrote:
>> It's been another week, and I still need approval for the build, doc,
>> and Darwin changes:
>
> So, the darwin bits look trivial enough, if the entire scheme is what
> people want to do.  My question would be, why do we want an option for
> this?  If the scheme works, why not just turn it on unconditionally?  If it
> doesn’t work, why add it?  If it isn’t good, why add it?  If it is good,
> why not do it?

It works in very specific circumstances, like assembler and linker versions.

> If it is just to reach compatibility with the debugger, then I’d rather
> either just mandate a certain debugger or autoconf for what the current
> debugger supports.  As of late people seem to just break the debugging
> experience with non-updated gdbs and assume that a newer gdb is used.

You cannot do that: unlike the assembler and linker used, which are
often hardcoded into gcc, the debugger can easily be changed below the
compiler's feet, so to speak.  Besides, on several platforms, you have
more than one debugger available (like gdb and dbx, or others), so this
isn't an option.  Apart from that, the debugging experience when
e.g. emitting very recent DWARF extensions and trying to use them with a
gdb that doesn't understand them usually leads to some debug info
missing.  In this case, emitting compressed debug with a debugger that
cannot read it leads to the debugger claiming (correctly, from its
point of view) that there's no debugging info present.  I don't want to
tell users who come complaining `I compiled with -g, but my debugger
tells me there's no debug info present': `look, your debugger lies, it
is present, but it cannot read it'.  That's a lot worse than the
DWARF extensions scenario above.

On top of all that, compressed debug is a tradeoff: in some cases it may
be worth it to save space on debug info if disk space is at a premium
for some reason (e.g. for release builds), but in others you want to
compile as fast as possible, but assembling and linking compressed debug
takes more CPU time.  Otherwise we could just as well default to -Os,
telling our users it's better for them since it generates faster and
smaller code, not minding the compile time cost and worse debugging
experience.

I at least don't wont to patronize our users like this.

	Rainer

-- 
-----------------------------------------------------------------------------
Rainer Orth, Center for Biotechnology, Bielefeld University

Re: [build, driver] RFC: Support compressed debug sections

[Mike Stump]

On Jun 4, 2014, at 1:54 AM, Rainer Orth <ro@CeBiTec.Uni-Bielefeld.DE> wrote:
> Mike Stump <mikestump@comcast.net> writes:
>> On Jun 3, 2014, at 3:40 AM, Rainer Orth <ro@CeBiTec.Uni-Bielefeld.DE> wrote:
>>> It's been another week, and I still need approval for the build, doc,
>>> and Darwin changes:
>> 
>> So, the darwin bits look trivial enough, if the entire scheme is what
>> people want to do.

The darwin bits are Ok.

Re: [build, driver] RFC: Support compressed debug sections

[Eric Christopher]

>> If it is just to reach compatibility with the debugger, then I’d rather
>> either just mandate a certain debugger or autoconf for what the current
>> debugger supports.  As of late people seem to just break the debugging
>> experience with non-updated gdbs and assume that a newer gdb is used.
>
> You cannot do that: unlike the assembler and linker used, which are
> often hardcoded into gcc, the debugger can easily be changed below the
> compiler's feet, so to speak.  Besides, on several platforms, you have
> more than one debugger available (like gdb and dbx, or others), so this
> isn't an option.  Apart from that, the debugging experience when
> e.g. emitting very recent DWARF extensions and trying to use them with a
> gdb that doesn't understand them usually leads to some debug info
> missing.  In this case, emitting compressed debug with a debugger that
> cannot read it leads to the debugger claiming (correctly, from its
> point of view) that there's no debugging info present.  I don't want to
> tell users who come complaining `I compiled with -g, but my debugger
> tells me there's no debug info present': `look, your debugger lies, it
> is present, but it cannot read it'.  That's a lot worse than the
> DWARF extensions scenario above.
>

Agreed :)

FWIW it's already a gas/assembler option, I'm curious about wanting to
expose it via the compiler?

> On top of all that, compressed debug is a tradeoff: in some cases it may
> be worth it to save space on debug info if disk space is at a premium
> for some reason (e.g. for release builds), but in others you want to
> compile as fast as possible, but assembling and linking compressed debug
> takes more CPU time.  Otherwise we could just as well default to -Os,
> telling our users it's better for them since it generates faster and
> smaller code, not minding the compile time cost and worse debugging
> experience.
>

FWIW I've found in some limited timing that compression is nearly
always worth it here at Google - even for compile time given the cost
of writing files versus cpu time. Might be worth making it a default
at some point in the future and making sure the option is invertible.

-eric

Re: [build, driver] RFC: Support compressed debug sections

[Rainer Orth]

Hi Gerald,

sorry for the delay, I've been away for a couple of days.

> On Tue, 3 Jun 2014, Rainer Orth wrote:
>> It's been another week, and I still need approval for the build, doc,
>> and Darwin changes:
>> 
>> 	https://gcc.gnu.org/ml/gcc-patches/2014-05/msg01860.html
>
> On the doc side, things are fine.
>
> Just a suggestion or two:
>
> +Produce compressed debug sections in DWARF format, if that is supported.
>
> Supported by what?

By the toolchain used.  TBH, I just copied that fragment from various
other debug options (-gstabs, -gcoff, -gdwarf-N).  Given the precedent
and the verbosity of a more detailed explanation, I'd leave this as is.

> "doesn't" -> "does not", especially given the emphasis we want to make
> here.

Good point, fixed.

> And could the "If the linker doesn't support writing compressed debug 
> sections, the option is rejected.  Otherwise, if the assembler doesn't 
> support them, @option{-gz} is silently ignored when producing object 
> files." be moved to the very end, or is this only applicable to the
> case where no type has been specified?

No, you're right: it's better to first explain the values for type in
the working case, then explain potential error scenarios.

The section now reads

@item -gz@r{[}=@var{type}@r{]}
@opindex gz
Produce compressed debug sections in DWARF format, if that is supported.
If @var{type} is not given, the default type depends on the capabilities
of the assembler and linker used.  @var{type} may be one of
@option{none} (don't compress debug sections), @option{zlib} (use zlib
compression in ELF gABI format), or @option{zlib-gnu} (use zlib
compression in traditional GNU format).  If the linker doesn't support
writing compressed debug sections, the option is rejected.  Otherwise,
if the assembler does not support them, @option{-gz} is silently ignored
when producing object files.

Thanks for your comments.

I'm still missing review of the build parts after three weeks and
several reminders, though.  Paolo, Nathanael, Alexandre, could one of
you please have a look?

Thanks.
        Rainer

-- 
-----------------------------------------------------------------------------
Rainer Orth, Center for Biotechnology, Bielefeld University

Re: [build, driver] RFC: Support compressed debug sections

[Rainer Orth]

Eric Christopher <echristo@gmail.com> writes:

>>> If it is just to reach compatibility with the debugger, then I’d rather
>>> either just mandate a certain debugger or autoconf for what the current
>>> debugger supports.  As of late people seem to just break the debugging
>>> experience with non-updated gdbs and assume that a newer gdb is used.
>>
>> You cannot do that: unlike the assembler and linker used, which are
>> often hardcoded into gcc, the debugger can easily be changed below the
>> compiler's feet, so to speak.  Besides, on several platforms, you have
>> more than one debugger available (like gdb and dbx, or others), so this
>> isn't an option.  Apart from that, the debugging experience when
>> e.g. emitting very recent DWARF extensions and trying to use them with a
>> gdb that doesn't understand them usually leads to some debug info
>> missing.  In this case, emitting compressed debug with a debugger that
>> cannot read it leads to the debugger claiming (correctly, from its
>> point of view) that there's no debugging info present.  I don't want to
>> tell users who come complaining `I compiled with -g, but my debugger
>> tells me there's no debug info present': `look, your debugger lies, it
>> is present, but it cannot read it'.  That's a lot worse than the
>> DWARF extensions scenario above.
>
> Agreed :)
>
> FWIW it's already a gas/assembler option, I'm curious about wanting to
> expose it via the compiler?

One reason: ease of use:

* -gz is far easier to use/type than -Wa,--compress-debug-sections +
  -Wl,--compress-debug-sections, and

* one common option irrespective of assemblers (the Solaris assembler
  will gain eventually gain compressed debug support, too) and linkers
  used (Solaris ld requires -z compress-sections=<type>), and even the
  Apple assembler might at some point ;-)

>> On top of all that, compressed debug is a tradeoff: in some cases it may
>> be worth it to save space on debug info if disk space is at a premium
>> for some reason (e.g. for release builds), but in others you want to
>> compile as fast as possible, but assembling and linking compressed debug
>> takes more CPU time.  Otherwise we could just as well default to -Os,
>> telling our users it's better for them since it generates faster and
>> smaller code, not minding the compile time cost and worse debugging
>> experience.
>
> FWIW I've found in some limited timing that compression is nearly
> always worth it here at Google - even for compile time given the cost
> of writing files versus cpu time. Might be worth making it a default
> at some point in the future and making sure the option is invertible.

One might be not so lucky with different/slower CPUs, though.  I wonder
how this would affect bootstrap times on my current SPARC systems ;-(

But yes, a configure option to default -gz to on would certainly be
helpful at some point.

	Rainer

-- 
-----------------------------------------------------------------------------
Rainer Orth, Center for Biotechnology, Bielefeld University

Re: [build, driver] RFC: Support compressed debug sections

[Paolo Bonzini]

Il 26/06/2014 15:16, Rainer Orth ha scritto:
> Hi Gerald,
>
> sorry for the delay, I've been away for a couple of days.
>
>> On Tue, 3 Jun 2014, Rainer Orth wrote:
>>> It's been another week, and I still need approval for the build, doc,
>>> and Darwin changes:
>>>
>>> 	https://gcc.gnu.org/ml/gcc-patches/2014-05/msg01860.html
>>
>> On the doc side, things are fine.
>>
>> Just a suggestion or two:
>>
>> +Produce compressed debug sections in DWARF format, if that is supported.
>>
>> Supported by what?
>
> By the toolchain used.  TBH, I just copied that fragment from various
> other debug options (-gstabs, -gcoff, -gdwarf-N).  Given the precedent
> and the verbosity of a more detailed explanation, I'd leave this as is.
>
>> "doesn't" -> "does not", especially given the emphasis we want to make
>> here.
>
> Good point, fixed.
>
>> And could the "If the linker doesn't support writing compressed debug
>> sections, the option is rejected.  Otherwise, if the assembler doesn't
>> support them, @option{-gz} is silently ignored when producing object
>> files." be moved to the very end, or is this only applicable to the
>> case where no type has been specified?
>
> No, you're right: it's better to first explain the values for type in
> the working case, then explain potential error scenarios.
>
> The section now reads
>
> @item -gz@r{[}=@var{type}@r{]}
> @opindex gz
> Produce compressed debug sections in DWARF format, if that is supported.
> If @var{type} is not given, the default type depends on the capabilities
> of the assembler and linker used.  @var{type} may be one of
> @option{none} (don't compress debug sections), @option{zlib} (use zlib
> compression in ELF gABI format), or @option{zlib-gnu} (use zlib
> compression in traditional GNU format).  If the linker doesn't support
> writing compressed debug sections, the option is rejected.  Otherwise,
> if the assembler does not support them, @option{-gz} is silently ignored
> when producing object files.
>
> Thanks for your comments.
>
> I'm still missing review of the build parts after three weeks and
> several reminders, though.  Paolo, Nathanael, Alexandre, could one of
> you please have a look?

Build changes are good, thanks.

Paolo

Re: [build, driver] RFC: Support compressed debug sections

[Eric Christopher]

On Thu, Jun 26, 2014 at 6:32 AM, Rainer Orth
<ro@cebitec.uni-bielefeld.de> wrote:
> Eric Christopher <echristo@gmail.com> writes:
>
>>>> If it is just to reach compatibility with the debugger, then I’d rather
>>>> either just mandate a certain debugger or autoconf for what the current
>>>> debugger supports.  As of late people seem to just break the debugging
>>>> experience with non-updated gdbs and assume that a newer gdb is used.
>>>
>>> You cannot do that: unlike the assembler and linker used, which are
>>> often hardcoded into gcc, the debugger can easily be changed below the
>>> compiler's feet, so to speak.  Besides, on several platforms, you have
>>> more than one debugger available (like gdb and dbx, or others), so this
>>> isn't an option.  Apart from that, the debugging experience when
>>> e.g. emitting very recent DWARF extensions and trying to use them with a
>>> gdb that doesn't understand them usually leads to some debug info
>>> missing.  In this case, emitting compressed debug with a debugger that
>>> cannot read it leads to the debugger claiming (correctly, from its
>>> point of view) that there's no debugging info present.  I don't want to
>>> tell users who come complaining `I compiled with -g, but my debugger
>>> tells me there's no debug info present': `look, your debugger lies, it
>>> is present, but it cannot read it'.  That's a lot worse than the
>>> DWARF extensions scenario above.
>>
>> Agreed :)
>>
>> FWIW it's already a gas/assembler option, I'm curious about wanting to
>> expose it via the compiler?
>
> One reason: ease of use:
>
> * -gz is far easier to use/type than -Wa,--compress-debug-sections +
>   -Wl,--compress-debug-sections, and
>

Very true. Maybe make it a -gcompress-dwarf-sections?

> * one common option irrespective of assemblers (the Solaris assembler
>   will gain eventually gain compressed debug support, too) and linkers
>   used (Solaris ld requires -z compress-sections=<type>), and even the
>   Apple assembler might at some point ;-)
>

The assembler itself does, but as far as I know none of the consumers
can deal with it. Right now it supports the same options as gas.

>>> On top of all that, compressed debug is a tradeoff: in some cases it may
>>> be worth it to save space on debug info if disk space is at a premium
>>> for some reason (e.g. for release builds), but in others you want to
>>> compile as fast as possible, but assembling and linking compressed debug
>>> takes more CPU time.  Otherwise we could just as well default to -Os,
>>> telling our users it's better for them since it generates faster and
>>> smaller code, not minding the compile time cost and worse debugging
>>> experience.
>>
>> FWIW I've found in some limited timing that compression is nearly
>> always worth it here at Google - even for compile time given the cost
>> of writing files versus cpu time. Might be worth making it a default
>> at some point in the future and making sure the option is invertible.
>
> One might be not so lucky with different/slower CPUs, though.  I wonder
> how this would affect bootstrap times on my current SPARC systems ;-(
>

I'd have thought you'd still largely be write bound for compilation. *shrug*

> But yes, a configure option to default -gz to on would certainly be
> helpful at some point.

*nod*

-eric