[PATCH 0/2] Fix implptr-optimized-out.exp fail in thumb mode

[PATCH 0/2] Fix implptr-optimized-out.exp fail in thumb mode

[Yao Qi]

implptr-optimized-out.exp uses main in assembly to generate debug
information, so it makes troubles in thumb mode because of the lsb of
main address.  Patch 1 is to switch to dwarf assembler to generate
assembly, so that it is flexible to adjust dwarf output.  Patch 2
is to compute the correct address of main.  We do the same in dwz.exp
too.

*** BLURB HERE ***

Yao Qi (2):
  Use Dwarf::assemble in implptr-optimized-out.exp
  Fix implptr-optimized-out.exp fail in thumb mode

 gdb/testsuite/gdb.dwarf2/implptr-optimized-out.S   | 166 ---------------------
 gdb/testsuite/gdb.dwarf2/implptr-optimized-out.exp |  96 +++++++++++-
 2 files changed, 93 insertions(+), 169 deletions(-)
 delete mode 100644 gdb/testsuite/gdb.dwarf2/implptr-optimized-out.S

-- 
1.9.3

[PATCH 2/2] Fix implptr-optimized-out.exp fail in thumb mode

[Yao Qi]

Hi,
I see the fail in gdb.dwarf2/implptr-optimized-out.exp in thumb mode

(gdb) p p->f^M
No symbol "p" in current context.^M
(gdb) FAIL: gdb.dwarf2/implptr-optimized-out.exp: p p->f

In thumb mode, the lsb of references to 'main' in the assembly
(produced by dwarf assember) is set, so the generated debug
information is incorrect.

in this patch, we add a label main_label inside function main.  Linker
doesn't set its lsb in thumb mode, and we can get function main's
address by 'main_label - $main_label_offset'.

gdb/testsuite:

2014-09-29  Yao Qi  <yao@codesourcery.com>

	* gdb.dwarf2/implptr-optimized-out.exp: Compile main.c to object.
	Calculate the offset of main_label to main.  Compile the generated
	asm file and link the executable.
	(Dwarf::assemble): Get address of main by
	main_label - $main_label_offset.
---
 gdb/testsuite/gdb.dwarf2/implptr-optimized-out.exp | 39 ++++++++++++++++++++--
 1 file changed, 36 insertions(+), 3 deletions(-)

diff --git a/gdb/testsuite/gdb.dwarf2/implptr-optimized-out.exp b/gdb/testsuite/gdb.dwarf2/implptr-optimized-out.exp
index 649f52d..534bed0 100644
--- a/gdb/testsuite/gdb.dwarf2/implptr-optimized-out.exp
+++ b/gdb/testsuite/gdb.dwarf2/implptr-optimized-out.exp
@@ -22,9 +22,35 @@ if {![dwarf2_support]} {
 standard_testfile main.c .S
 set executable ${testfile}
 
+if  {[gdb_compile ${srcdir}/${subdir}/${srcfile} ${binfile}1.o \
+	  object {}] != ""} {
+    return -1
+}
+# Start GDB and load object file, compute the offset from main to
+# main_label which are needed in the Dwarf Assembler below.
+clean_restart ${binfile}1.o
+
+set main_label_offset ""
+set test "p main_label - main"
+gdb_test_multiple $test $test {
+    -re ".* = ($decimal)\r\n$gdb_prompt $" {
+	set main_label_offset $expect_out(1,string)
+    }
+}
+
+if { $main_label_offset == "" } {
+    # Bail out here, because we can't do the following tests if
+    # $main_label_offset is unknown.
+    return -1
+}
+
+gdb_exit
+
 # Create the DWARF.
 set asm_file [standard_output_file $srcfile2]
 Dwarf::assemble $asm_file {
+    global main_label_offset
+
     cu { version 3 } {
 	compile_unit {
 	    {producer "GNU C 4.4.3"}
@@ -52,8 +78,8 @@ Dwarf::assemble $asm_file {
 
 	    subprogram {
 		{name main}
-		{low_pc main addr}
-		{high_pc main+0x100 addr}
+		{low_pc "main_label - $main_label_offset" addr}
+		{high_pc "main_label - $main_label_offset + 0x100" addr}
 		{type :$int_label}
 		{external 1 flag}
 	    } {
@@ -80,10 +106,17 @@ Dwarf::assemble $asm_file {
     }
 }
 
-if [prepare_for_testing ${testfile}.exp $executable "${asm_file} ${srcfile}" {}] {
+if  {[gdb_compile $asm_file ${binfile}0.o object {}] != ""} {
     return -1
 }
 
+if  {[gdb_compile [list ${binfile}0.o ${binfile}1.o] \
+	  "${binfile}" executable {}] != ""} {
+    return -1
+}
+
+clean_restart ${testfile}
+
 # DW_OP_GNU_implicit_pointer implementation requires a valid frame.
 if ![runto_main] {
     return -1
-- 
1.9.3

Re: [PATCH 2/2] Fix implptr-optimized-out.exp fail in thumb mode

[Pedro Alves]

On 09/29/2014 01:52 AM, Yao Qi wrote:
> Hi,
> I see the fail in gdb.dwarf2/implptr-optimized-out.exp in thumb mode
> 
> (gdb) p p->f^M
> No symbol "p" in current context.^M
> (gdb) FAIL: gdb.dwarf2/implptr-optimized-out.exp: p p->f
> 
> In thumb mode, the lsb of references to 'main' in the assembly
> (produced by dwarf assember) is set, so the generated debug
> information is incorrect.
> 
> in this patch, we add a label main_label inside function main.

Hmm, I think I'm missing something.  I'm not where this "main_label"
label is coming from?

Thanks,
Pedro Alves

Re: [PATCH 2/2] Fix implptr-optimized-out.exp fail in thumb mode

[Yao Qi]

Pedro Alves <palves@redhat.com> writes:

> Hmm, I think I'm missing something.  I'm not where this "main_label"
> label is coming from?

Ur... main_label is added by this patch
https://sourceware.org/ml/gdb-patches/2014-09/msg00497.html which is
pending for review too.  I forget to mention that this patch depends on
the gdb.dwarf2/dwz.exp patch, sorry.

-- 
Yao (齐尧)

Re: [PATCH 2/2] Fix implptr-optimized-out.exp fail in thumb mode

[Doug Evans]

On Sun, Sep 28, 2014 at 8:52 PM, Yao Qi <yao@codesourcery.com> wrote:
> Hi,
> I see the fail in gdb.dwarf2/implptr-optimized-out.exp in thumb mode
>
> (gdb) p p->f^M
> No symbol "p" in current context.^M
> (gdb) FAIL: gdb.dwarf2/implptr-optimized-out.exp: p p->f
>
> In thumb mode, the lsb of references to 'main' in the assembly
> (produced by dwarf assember) is set, so the generated debug
> information is incorrect.
>
> in this patch, we add a label main_label inside function main.  Linker
> doesn't set its lsb in thumb mode, and we can get function main's
> address by 'main_label - $main_label_offset'.
>
> gdb/testsuite:
>
> 2014-09-29  Yao Qi  <yao@codesourcery.com>
>
>         * gdb.dwarf2/implptr-optimized-out.exp: Compile main.c to object.
>         Calculate the offset of main_label to main.  Compile the generated
>         asm file and link the executable.
>         (Dwarf::assemble): Get address of main by
>         main_label - $main_label_offset.
> ---
>  gdb/testsuite/gdb.dwarf2/implptr-optimized-out.exp | 39 ++++++++++++++++++++--
>  1 file changed, 36 insertions(+), 3 deletions(-)
>
> diff --git a/gdb/testsuite/gdb.dwarf2/implptr-optimized-out.exp b/gdb/testsuite/gdb.dwarf2/implptr-optimized-out.exp
> index 649f52d..534bed0 100644
> --- a/gdb/testsuite/gdb.dwarf2/implptr-optimized-out.exp
> +++ b/gdb/testsuite/gdb.dwarf2/implptr-optimized-out.exp
> @@ -22,9 +22,35 @@ if {![dwarf2_support]} {
>  standard_testfile main.c .S
>  set executable ${testfile}
>
> +if  {[gdb_compile ${srcdir}/${subdir}/${srcfile} ${binfile}1.o \
> +         object {}] != ""} {
> +    return -1
> +}
> +# Start GDB and load object file, compute the offset from main to
> +# main_label which are needed in the Dwarf Assembler below.
> +clean_restart ${binfile}1.o
> +
> +set main_label_offset ""
> +set test "p main_label - main"
> +gdb_test_multiple $test $test {
> +    -re ".* = ($decimal)\r\n$gdb_prompt $" {
> +       set main_label_offset $expect_out(1,string)
> +    }
> +}
> +
> +if { $main_label_offset == "" } {
> +    # Bail out here, because we can't do the following tests if
> +    # $main_label_offset is unknown.
> +    return -1
> +}
> +
> +gdb_exit
> +
>  # Create the DWARF.
>  set asm_file [standard_output_file $srcfile2]
>  Dwarf::assemble $asm_file {
> +    global main_label_offset
> +
>      cu { version 3 } {
>         compile_unit {
>             {producer "GNU C 4.4.3"}
> @@ -52,8 +78,8 @@ Dwarf::assemble $asm_file {
>
>             subprogram {
>                 {name main}
> -               {low_pc main addr}
> -               {high_pc main+0x100 addr}
> +               {low_pc "main_label - $main_label_offset" addr}
> +               {high_pc "main_label - $main_label_offset + 0x100" addr}
>                 {type :$int_label}
>                 {external 1 flag}
>             } {
> @@ -80,10 +106,17 @@ Dwarf::assemble $asm_file {
>      }
>  }
>
> -if [prepare_for_testing ${testfile}.exp $executable "${asm_file} ${srcfile}" {}] {
> +if  {[gdb_compile $asm_file ${binfile}0.o object {}] != ""} {
>      return -1
>  }
>
> +if  {[gdb_compile [list ${binfile}0.o ${binfile}1.o] \
> +         "${binfile}" executable {}] != ""} {
> +    return -1
> +}
> +
> +clean_restart ${testfile}
> +
>  # DW_OP_GNU_implicit_pointer implementation requires a valid frame.
>  if ![runto_main] {
>      return -1

Hi.

One question that comes to mind is: If this solution is going to
proliferate it would be good to convince ourselves there's no better
solution.  I'm ok with this as a one-off here and there, but I'd like
to understand how many more of these will there be.  Plus I can
imagine of course the number growing over time.
Can we, for example, enhance the dwarf assembler and provide a hook
for the thumb target to use to fix this there?

But *if* we do decide there's no better solution, there's a lot of
boilerplate here.
Can we tuck it away in a utility?

Re: [PATCH 2/2] Fix implptr-optimized-out.exp fail in thumb mode

[Yao Qi]

Doug Evans <dje@google.com> writes:

> One question that comes to mind is: If this solution is going to
> proliferate it would be good to convince ourselves there's no better
> solution.  I'm ok with this as a one-off here and there, but I'd like
> to understand how many more of these will there be.  Plus I can
> imagine of course the number growing over time.

There are three, dwz.exp, implptr-optimized-out.exp and
dw2-ifort-parameter.exp, but you are right, the number will grow.

> Can we, for example, enhance the dwarf assembler and provide a hook
> for the thumb target to use to fix this there?

ppc64 target has the similar problem too.  We need a way suitable for
{thumb, ppc64, other} x {gcc, clang}.

Hacking dwarf assembler doesn't help much, because we are still unable
to get the right function address.

>
> But *if* we do decide there's no better solution, there's a lot of
> boilerplate here.

Let me list the solutions I thought about and tried, so that we can
evaluate which one is the best.

 - Tweak dwarf assembler to generate assembly debug info together with
   __thumb__ and __thumb2__, like

   #if defined (__thumb__) || defined (__thumb2__)
   .uleb128        main-1            /* DW_AT_low_pc */
   #else
   .uleb128        main              /* DW_AT_low_pc */
   #endif

   this doesn't work because main in "main-1" is resolved to the function
   address (without lsb set).  Unfortunately, "main-1+1" is resolved to
   the function address *with* lsb set.

 - The approach I proposed here, which should fix the problem on ppc64
   (I didn't verify that on the real hardware).

 - Fix ld that stop setting function address lsb if they are in debug
   info.  I didn't try.

 - Make use of local symbols.  I find gcc/clang generates local symbol on the
   entry of the function but looks "-Wa,-L" doesn't keep them.

-- 
Yao (齐尧)

[PATCH 1/2] Use Dwarf::assemble in implptr-optimized-out.exp

[Yao Qi]

This patch is to use dwarf::assemble to generate debug information, and
remove implptr-optimized-out.S as a result.  The dwarf assembler output
is identical to original implptr-optimized-out.S.

gdb/testsuite:

2014-09-29  Yao Qi  <yao@codesourcery.com>

	* gdb.dwarf2/implptr-optimized-out.exp: Use Dwarf::assemble to
	produce debug information.
	* gdb.dwarf2/implptr-optimized-out.S: Removed.
---
 gdb/testsuite/gdb.dwarf2/implptr-optimized-out.S   | 166 ---------------------
 gdb/testsuite/gdb.dwarf2/implptr-optimized-out.exp |  63 +++++++-
 2 files changed, 60 insertions(+), 169 deletions(-)
 delete mode 100644 gdb/testsuite/gdb.dwarf2/implptr-optimized-out.S

diff --git a/gdb/testsuite/gdb.dwarf2/implptr-optimized-out.S b/gdb/testsuite/gdb.dwarf2/implptr-optimized-out.S
deleted file mode 100644
index eeebd54..0000000
--- a/gdb/testsuite/gdb.dwarf2/implptr-optimized-out.S
+++ /dev/null
@@ -1,166 +0,0 @@
-/* Copyright 2010-2014 Free Software Foundation, Inc.
-
-   This program is free software; you can redistribute it and/or modify
-   it under the terms of the GNU General Public License as published by
-   the Free Software Foundation; either version 3 of the License, or
-   (at your option) any later version.
-
-   This program is distributed in the hope that it will be useful,
-   but WITHOUT ANY WARRANTY; without even the implied warranty of
-   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-   GNU General Public License for more details.
-
-   You should have received a copy of the GNU General Public License
-   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
-
-	.section	.debug_info
-d:
-	.4byte	debug_end - 1f	/* Length of Compilation Unit Info */
-1:
-	.2byte	0x3	/* DWARF version number */
-	.4byte	.Ldebug_abbrev0	/* Offset Into Abbrev. Section */
-	.byte	0x4	/* Pointer Size (in bytes) */
-	.uleb128 0x1	/* (DIE (0xb) DW_TAG_compile_unit) */
-	.ascii "GNU C 4.4.3\0"	/* DW_AT_producer */
-	.byte	0x1	/* DW_AT_language */
-	.ascii "1.c\0"	/* DW_AT_name */
-
-.Ltype_int:
-	.uleb128 0x7	/* DW_TAG_base_type */
-	.byte	0x4	/* DW_AT_byte_size */
-	.byte	0x5	/* DW_AT_encoding */
-	.ascii "int\0"	/* DW_AT_name */
-
-.Ltype_struct:
-	.uleb128 0x2	/* DW_TAG_structure_type */
-	.ascii "s\0"	/* DW_AT_name */
-	.byte	4	/* DW_AT_byte_size */
-
-	.uleb128 0x3	/* DW_TAG_member */
-	.ascii "f\0"	/* DW_AT_name */
-	.4byte	.Ltype_int - d	/* DW_AT_type */
-	.byte	0	/* DW_AT_data_member_location */
-
-	.byte	0x0	/* end of children of DW_TAG_structure_type */
-
-	.uleb128	6			/* Abbrev: DW_TAG_subprogram */
-	.ascii		"main\0"		/* DW_AT_name */
-	.4byte		main			/* DW_AT_low_pc */
-	.4byte		main + 0x100		/* DW_AT_high_pc */
-	.4byte		.Ltype_int - d		/* DW_AT_type */
-	.byte		1			/* DW_AT_external */
-
-.Ltype_structptr:
-	.uleb128 0x5	/* DW_TAG_pointer_type */
-	.byte	0x4	/* DW_AT_byte_size */
-	.4byte	.Ltype_struct - d	/* DW_AT_type */
-
-.Lvar_out:
-	.uleb128 0x4	/* (DW_TAG_variable) */
-	.ascii "v\0"	/* DW_AT_name */
-	.byte	0	/* DW_AT_location: DW_FORM_block1 */
-	.4byte	.Ltype_struct - d	/* DW_AT_type */
-
-	.uleb128 0x4	/* (DW_TAG_variable) */
-	.ascii "p\0"	/* DW_AT_name */
-	.byte	2f - 1f	/* DW_AT_location: DW_FORM_block1 */
-1:
-	.byte	0xf2	/* DW_OP_GNU_implicit_pointer */
-	.4byte	.Lvar_out	/* referenced DIE, section-relative! */
-	.sleb128	0	/* offset */
-2:
-	.4byte	.Ltype_structptr - d	/* DW_AT_type */
-
-	.byte	0x0	/* end of children of main */
-
-	.byte	0x0	/* end of children of CU */
-debug_end:
-
-	.section	.debug_abbrev
-.Ldebug_abbrev0:
-
-	.uleb128 0x1	/* (abbrev code) */
-	.uleb128 0x11	/* (TAG: DW_TAG_compile_unit) */
-	.byte	0x1	/* DW_children_yes */
-	.uleb128 0x25	/* (DW_AT_producer) */
-	.uleb128 0x8	/* (DW_FORM_string) */
-	.uleb128 0x13	/* (DW_AT_language) */
-	.uleb128 0xb	/* (DW_FORM_data1) */
-	.uleb128 0x3	/* (DW_AT_name) */
-	.uleb128 0x8	/* (DW_FORM_string) */
-	.byte	0x0
-	.byte	0x0
-
-	.uleb128 0x2	/* (abbrev code) */
-	.uleb128 0x13	/* (TAG: DW_TAG_structure_type) */
-	.byte	0x1	/* DW_children_yes */
-	.uleb128 0x3	/* (DW_AT_name) */
-	.uleb128 0x8	/* (DW_FORM_string) */
-	.uleb128 0xb	/* (DW_AT_byte_size) */
-	.uleb128 0xb	/* (DW_FORM_data1) */
-	.byte	0
-	.byte	0
-
-	.uleb128 0x3	/* (abbrev code) */
-	.uleb128 0xd	/* (TAG: DW_TAG_member) */
-	.byte	0	/* DW_children_no */
-	.uleb128 0x3	/* (DW_AT_name) */
-	.uleb128 0x8	/* (DW_FORM_string) */
-	.uleb128 0x49	/* (DW_AT_type) */
-	.uleb128 0x13	/* (DW_FORM_ref4) */
-	.uleb128 0x38	/* (DW_AT_data_member_location) */
-	.uleb128 0xb	/* (DW_FORM_data1) */
-	.byte	0
-	.byte	0
-
-	.uleb128 0x4	/* (abbrev code) */
-	.uleb128 0x34	/* (TAG: DW_TAG_variable) */
-	.byte	0x0	/* DW_children_yes */
-	.uleb128 0x3	/* (DW_AT_name) */
-	.uleb128 0x8	/* (DW_FORM_string) */
-	.uleb128 0x02	/* (DW_AT_location) */
-	.uleb128 0xa	/* (DW_FORM_block1) */
-	.uleb128 0x49	/* (DW_AT_type) */
-	.uleb128 0x13	/* (DW_FORM_ref4) */
-	.byte	0x0
-	.byte	0x0
-
-	.uleb128 0x5	/* (abbrev code) */
-	.uleb128 0xf	/* (TAG: DW_TAG_pointer_type) */
-	.byte	0x0	/* DW_children_no */
-	.uleb128 0xb	/* (DW_AT_byte_size) */
-	.uleb128 0xb	/* (DW_FORM_data1) */
-	.uleb128 0x49	/* (DW_AT_type) */
-	.uleb128 0x13	/* (DW_FORM_ref4) */
-	.byte	0x0
-	.byte	0x0
-
-	.uleb128	6			/* Abbrev code */
-	.uleb128	0x2e			/* DW_TAG_subprogram */
-	.byte		1			/* has_children */
-	.uleb128	0x3			/* DW_AT_name */
-	.uleb128	0x8			/* DW_FORM_string */
-	.uleb128	0x11			/* DW_AT_low_pc */
-	.uleb128	0x1			/* DW_FORM_addr */
-	.uleb128	0x12			/* DW_AT_high_pc */
-	.uleb128	0x1			/* DW_FORM_addr */
-	.uleb128	0x49			/* DW_AT_type */
-	.uleb128	0x13			/* DW_FORM_ref4 */
-	.uleb128	0x3f			/* DW_AT_external */
-	.uleb128	0xc			/* DW_FORM_flag */
-	.byte		0x0			/* Terminator */
-	.byte		0x0			/* Terminator */
-
-	.uleb128 0x7	/* (abbrev code) */
-	.uleb128 0x24	/* (TAG: DW_TAG_base_type) */
-	.byte	0	/* DW_children_no */
-	.uleb128 0xb	/* (DW_AT_byte_size) */
-	.uleb128 0xb	/* (DW_FORM_data1) */
-	.uleb128 0x3e	/* (DW_AT_encoding) */
-	.uleb128 0xb	/* (DW_FORM_data1) */
-	.uleb128 0x3	/* (DW_AT_name) */
-	.uleb128 0x8	/* (DW_FORM_string) */
-	.byte	0
-	.byte	0
-
-	.byte	0x0
diff --git a/gdb/testsuite/gdb.dwarf2/implptr-optimized-out.exp b/gdb/testsuite/gdb.dwarf2/implptr-optimized-out.exp
index 26ca407..649f52d 100644
--- a/gdb/testsuite/gdb.dwarf2/implptr-optimized-out.exp
+++ b/gdb/testsuite/gdb.dwarf2/implptr-optimized-out.exp
@@ -19,11 +19,68 @@ if {![dwarf2_support]} {
     return 0  
 }
 
-standard_testfile .S
-set mainfile main.c
+standard_testfile main.c .S
 set executable ${testfile}
 
-if [prepare_for_testing ${testfile}.exp $executable "${srcfile} ${mainfile}" {}] {
+# Create the DWARF.
+set asm_file [standard_output_file $srcfile2]
+Dwarf::assemble $asm_file {
+    cu { version 3 } {
+	compile_unit {
+	    {producer "GNU C 4.4.3"}
+	    {language @DW_LANG_C89}
+	    {name 1.c}
+	} {
+	    declare_labels int_label struct_label pointer_label variable_label
+
+	    int_label: base_type {
+		{byte_size 4 sdata}
+		{encoding @DW_ATE_signed}
+		{name int}
+	    }
+
+	    struct_label: structure_type {
+		{name s}
+		{byte_size 4 sdata}
+	    } {
+		member {
+		    {name f}
+		    {type :$int_label}
+		    {data_member_location 0 data1}
+		}
+	    }
+
+	    subprogram {
+		{name main}
+		{low_pc main addr}
+		{high_pc main+0x100 addr}
+		{type :$int_label}
+		{external 1 flag}
+	    } {
+		pointer_label: pointer_type {
+		    {byte_size 4 sdata}
+		    {type :$struct_label}
+		}
+
+		variable_label: DW_TAG_variable {
+		    {name v}
+		    {location {} DW_FORM_block1}
+		    {type :$struct_label}
+		}
+
+		DW_TAG_variable {
+		    {name p}
+		    {location {
+			GNU_implicit_pointer $variable_label 0
+		    } SPECIAL_expr}
+		    {type :$pointer_label}
+		}
+	    }
+	}
+    }
+}
+
+if [prepare_for_testing ${testfile}.exp $executable "${asm_file} ${srcfile}" {}] {
     return -1
 }
 
-- 
1.9.3

Re: [PATCH 0/2] Fix implptr-optimized-out.exp fail in thumb mode

[Yao Qi]

Yao Qi <yao@codesourcery.com> writes:

> implptr-optimized-out.exp uses main in assembly to generate debug
> information, so it makes troubles in thumb mode because of the lsb of
> main address.  Patch 1 is to switch to dwarf assembler to generate
> assembly, so that it is flexible to adjust dwarf output.  Patch 2
> is to compute the correct address of main.  We do the same in dwz.exp
> too.

Ping.

-- 
Yao (齐尧)