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* [PATCH v3 1/9] Add configure check to test if gcc supports attribute ifunc.
@ 2016-08-24 14:05 Stefan Liebler
  2016-08-24 14:05 ` [PATCH v3 3/9] s390: Refactor ifunc resolvers due to false debuginfo Stefan Liebler
                   ` (10 more replies)
  0 siblings, 11 replies; 27+ messages in thread
From: Stefan Liebler @ 2016-08-24 14:05 UTC (permalink / raw)
  To: libc-alpha; +Cc: stli, fweimer, murphyp, schwab, joseph_myers

This patch adds a configure check to test if gcc supports attribute ifunc.
The support can either be enabled in <gcc-src>/gcc/config.gcc for one
architecture in general by setting default_gnu_indirect_function variable to yes
or by configuring gcc with --enable-gnu-indirect-function.

The next patch rewrites libc_ifunc macro to use gcc attribute ifunc instead
of inline assembly to generate the IFUNC symbols due to false debuginfo.

If gcc does not support attribute ifunc, the old approach for generating
ifunc'ed symbols is used. Then the debug-information is false. Thus it is
recommended to use a gcc with indirect function support (See notes in INSTALL).
After this patch-series these inline assemblies for ifunc-handling are not
scattered in multiple files but are used only indirect via ifunc-macros
and can simply removed in libc-symbols.h in future.

If glibc is configured with --enable-multi-arch and gcc does not support
attribute ifunc, a configure warning is dumped!

This NEWS entry will be added:
* For multi-arch support it is recommended to use a GCC with gnu-indirect-function
  support as it is used to generate ifunc'ed symbols with correct
  debug-information. This support can either be enabled by configuring GCC with
  '--enable-gnu-indirect-function' or by enabling it by default by setting
  'default_gnu_indirect_function' variable for a particular architecture in
  gcc source file 'gcc/config.gcc'.

ChangeLog:

	* config.h.in (HAVE_GCC_IFUNC): New undef.
	* configure.ac: Add check if gcc supports attribute ifunc feature.
	* configure: Regenerated.
	* manual/install.texi: Add recommendation for gcc with
	indirect-function support.
	* INSTALL: Regenerated.
---
 INSTALL             |  8 ++++++++
 config.h.in         |  3 +++
 configure           | 42 ++++++++++++++++++++++++++++++++++++++++++
 configure.ac        | 33 +++++++++++++++++++++++++++++++++
 manual/install.texi |  7 +++++++
 5 files changed, 93 insertions(+)

diff --git a/INSTALL b/INSTALL
index ec3445f..1a67891 100644
--- a/INSTALL
+++ b/INSTALL
@@ -359,6 +359,14 @@ build the GNU C Library:
      better code.  As of release time, GCC 5.3 is the newest compiler
      verified to work to build the GNU C Library.
 
+     For multi-arch support it is recommended to use a GCC with
+     gnu-indirect-function support as it is used to generate ifunc'ed
+     symbols with correct debug-information.  This support can either be
+     enabled by configuring GCC with '--enable-gnu-indirect-function' or
+     by enabling it by default by setting
+     'default_gnu_indirect_function' variable for a particular
+     architecture in gcc source file 'gcc/config.gcc'.
+
      You can use whatever compiler you like to compile programs that use
      the GNU C Library.
 
diff --git a/config.h.in b/config.h.in
index 856ef6a..9f5c5ff 100644
--- a/config.h.in
+++ b/config.h.in
@@ -171,6 +171,9 @@
 /* Define to 1 if STT_GNU_IFUNC support actually works.  */
 #define HAVE_IFUNC 0
 
+/* Define if gcc supports attribute ifunc.  */
+#undef HAVE_GCC_IFUNC
+
 /* Define if the linker defines __ehdr_start.  */
 #undef HAVE_EHDR_START
 
diff --git a/configure b/configure
index 17625e1..8ffc2b5 100755
--- a/configure
+++ b/configure
@@ -3914,6 +3914,36 @@ fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_ld_gnu_indirect_function" >&5
 $as_echo "$libc_cv_ld_gnu_indirect_function" >&6; }
 
+# Check if gcc supports attribute ifunc as it is used in libc_ifunc macro.
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for gcc attribute ifunc support" >&5
+$as_echo_n "checking for gcc attribute ifunc support... " >&6; }
+if ${libc_cv_gcc_indirect_function+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  cat > conftest.c <<EOF
+extern int func (int);
+int used_func (int a)
+{
+  return a;
+}
+static void *resolver ()
+{
+  return &used_func;
+}
+extern __typeof (func) func __attribute__ ((ifunc ("resolver")));
+EOF
+libc_cv_gcc_indirect_function=no
+if ${CC-cc} -c conftest.c -o conftest.o 1>&5 \
+   2>&5 ; then
+  if $READELF -s conftest.o | grep IFUNC >/dev/null 2>&5; then
+    libc_cv_gcc_indirect_function=yes
+  fi
+fi
+rm -f conftest*
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gcc_indirect_function" >&5
+$as_echo "$libc_cv_gcc_indirect_function" >&6; }
+
 if test x"$libc_cv_ld_gnu_indirect_function" != xyes; then
   if test x"$multi_arch" = xyes; then
     as_fn_error $? "--enable-multi-arch support requires assembler and linker support" "$LINENO" 5
@@ -3921,6 +3951,13 @@ if test x"$libc_cv_ld_gnu_indirect_function" != xyes; then
     multi_arch=no
   fi
 fi
+if test x"$libc_cv_gcc_indirect_function" != xyes &&
+   test x"$multi_arch" = xyes; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: --enable-multi-arch support recommends a gcc with gnu-indirect-function support.
+Please use a gcc which supports it by default or configure gcc with --enable-gnu-indirect-function" >&5
+$as_echo "$as_me: WARNING: --enable-multi-arch support recommends a gcc with gnu-indirect-function support.
+Please use a gcc which supports it by default or configure gcc with --enable-gnu-indirect-function" >&2;}
+fi
 multi_arch_d=
 if test x"$multi_arch" != xno; then
   multi_arch_d=/multiarch
@@ -6504,6 +6541,11 @@ if test x"$libc_cv_ld_gnu_indirect_function" = xyes; then
 
 fi
 
+if test x"$libc_cv_gcc_indirect_function" = xyes; then
+  $as_echo "#define HAVE_GCC_IFUNC 1" >>confdefs.h
+
+fi
+
 # This is far from the AC_ARG_ENABLE that sets it so that a sysdeps
 # configure fragment can override the value to prevent this AC_DEFINE.
 
diff --git a/configure.ac b/configure.ac
index 33bcd62..643002f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -634,6 +634,30 @@ if ${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS \
 fi
 rm -f conftest*])
 
+# Check if gcc supports attribute ifunc as it is used in libc_ifunc macro.
+AC_CACHE_CHECK([for gcc attribute ifunc support],
+	       libc_cv_gcc_indirect_function, [dnl
+cat > conftest.c <<EOF
+extern int func (int);
+int used_func (int a)
+{
+  return a;
+}
+static void *resolver ()
+{
+  return &used_func;
+}
+extern __typeof (func) func __attribute__ ((ifunc ("resolver")));
+EOF
+libc_cv_gcc_indirect_function=no
+if ${CC-cc} -c conftest.c -o conftest.o 1>&AS_MESSAGE_LOG_FD \
+   2>&AS_MESSAGE_LOG_FD ; then
+  if $READELF -s conftest.o | grep IFUNC >/dev/null 2>&AS_MESSAGE_LOG_FD; then
+    libc_cv_gcc_indirect_function=yes
+  fi
+fi
+rm -f conftest*])
+
 if test x"$libc_cv_ld_gnu_indirect_function" != xyes; then
   if test x"$multi_arch" = xyes; then
     AC_MSG_ERROR([--enable-multi-arch support requires assembler and linker support])
@@ -641,6 +665,11 @@ if test x"$libc_cv_ld_gnu_indirect_function" != xyes; then
     multi_arch=no
   fi
 fi
+if test x"$libc_cv_gcc_indirect_function" != xyes &&
+   test x"$multi_arch" = xyes; then
+  AC_MSG_WARN([--enable-multi-arch support recommends a gcc with gnu-indirect-function support.
+Please use a gcc which supports it by default or configure gcc with --enable-gnu-indirect-function])
+fi
 multi_arch_d=
 if test x"$multi_arch" != xno; then
   multi_arch_d=/multiarch
@@ -1770,6 +1799,10 @@ if test x"$libc_cv_ld_gnu_indirect_function" = xyes; then
   AC_DEFINE(HAVE_IFUNC)
 fi
 
+if test x"$libc_cv_gcc_indirect_function" = xyes; then
+  AC_DEFINE(HAVE_GCC_IFUNC)
+fi
+
 # This is far from the AC_ARG_ENABLE that sets it so that a sysdeps
 # configure fragment can override the value to prevent this AC_DEFINE.
 AC_SUBST(use_nscd)
diff --git a/manual/install.texi b/manual/install.texi
index 79ee45f..d738ee0 100644
--- a/manual/install.texi
+++ b/manual/install.texi
@@ -402,6 +402,13 @@ the newest version of the compiler that is known to work for building
 release time, GCC 5.3 is the newest compiler verified to work to build
 @theglibc{}.
 
+For multi-arch support it is recommended to use a GCC with gnu-indirect-function
+support as it is used to generate ifunc'ed symbols with correct
+debug-information. This support can either be enabled by configuring GCC with
+@samp{--enable-gnu-indirect-function} or by enabling it by default by setting
+@samp{default_gnu_indirect_function} variable for a particular architecture in
+gcc source file @file{gcc/config.gcc}.
+
 You can use whatever compiler you like to compile programs that use
 @theglibc{}.
 
-- 
2.3.0

^ permalink raw reply	[flat|nested] 27+ messages in thread
end of thread, other threads:[~2016-10-07  9:19 UTC | newest]

Thread overview: 27+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2016-08-24 14:05 [PATCH v3 1/9] Add configure check to test if gcc supports attribute ifunc Stefan Liebler
2016-08-24 14:05 ` [PATCH v3 3/9] s390: Refactor ifunc resolvers due to false debuginfo Stefan Liebler
2016-08-30 12:31   ` Florian Weimer
2016-08-30 14:12     ` Stefan Liebler
2016-08-24 14:05 ` [PATCH v3 2/9] Use gcc attribute ifunc in libc_ifunc macro instead of inline assembly " Stefan Liebler
2016-08-29 20:16   ` Paul E. Murphy
2016-08-30 14:12     ` Stefan Liebler
2016-09-29 18:38   ` Adhemerval Zanella
2016-09-30 13:45     ` Stefan Liebler
2016-10-04 13:14       ` Adhemerval Zanella
2016-08-24 14:05 ` [PATCH v3 9/9] Use libc_ifunc macro for siglongjmp, longjmp in libpthread Stefan Liebler
2016-10-06 11:59   ` Florian Weimer
2016-08-24 14:05 ` [PATCH v3 8/9] Use libc_ifunc macro for vfork " Stefan Liebler
2016-08-30 12:40   ` Florian Weimer
2016-08-24 14:05 ` [PATCH v3 4/9] i386, x86: Use libc_ifunc macro for time, gettimeofday Stefan Liebler
2016-09-29 14:34   ` Andreas Schwab
2016-08-24 14:05 ` [PATCH v3 5/9] ppc: " Stefan Liebler
2016-08-30 13:46   ` Paul E. Murphy
2016-08-24 14:05 ` [PATCH v3 6/9] Use libc_ifunc macro for clock_* symbols in librt Stefan Liebler
2016-08-30 12:39   ` Florian Weimer
2016-08-24 17:02 ` [PATCH v3 7/9] Use libc_ifunc macro for system in libpthread Stefan Liebler
2016-08-30 12:39   ` Florian Weimer
2016-08-29  9:34 ` [PATCH v3 1/9] Add configure check to test if gcc supports attribute ifunc Florian Weimer
2016-08-30 14:12   ` Stefan Liebler
2016-09-05  7:13 ` [PING][PATCH " Stefan Liebler
2016-09-29 13:50   ` Stefan Liebler
2016-10-07  9:19 ` [PATCH " Stefan Liebler

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