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Add configure check to test if gcc supports attribute ifunc.
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! 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.
This commit is contained in:
Stefan Liebler
parent
1e7c8fcca5
commit
022dfdce00
@ -1,3 +1,12 @@
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2016-10-07 Stefan Liebler <stli@linux.vnet.ibm.com>
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* config.h.in (HAVE_GCC_IFUNC): New undef.
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* configure.ac: Add check if gcc supports attribute ifunc feature.
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* configure: Regenerated.
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* manual/install.texi: Add recommendation for gcc with
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indirect-function support.
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* INSTALL: Regenerated.
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2016-10-06 Joseph Myers <joseph@codesourcery.com>
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* math/math.h [__GLIBC_USE (IEC_60559_BFP_EXT)] (iseqsig): New
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9
INSTALL
9
INSTALL
@ -359,6 +359,15 @@ build the GNU C Library:
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better code. As of release time, GCC 5.3 is the newest compiler
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verified to work to build the GNU C Library.
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For multi-arch support it is recommended to use a GCC which has
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been built with support for GNU indirect functions. This ensures
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that correct debugging information is generated for functions
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selected by IFUNC resolvers. This support can either be enabled by
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configuring GCC with '--enable-gnu-indirect-function', or by
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enabling it by default by setting 'default_gnu_indirect_function'
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variable for a particular architecture in the GCC source file
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'gcc/config.gcc'.
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You can use whatever compiler you like to compile programs that use
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the GNU C Library.
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9
NEWS
9
NEWS
@ -76,6 +76,15 @@ Version 2.25
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The glibc stub resolver did not support these hooks, but the header file
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did not reflect that.
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* For multi-arch support it is recommended to use a GCC which has
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been built with support for GNU indirect functions. This ensures
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that correct debugging information is generated for functions
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selected by IFUNC resolvers. This support can either be enabled by
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configuring GCC with '--enable-gnu-indirect-function', or by
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enabling it by default by setting 'default_gnu_indirect_function'
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variable for a particular architecture in the GCC source file
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'gcc/config.gcc'.
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Security related changes:
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On ARM EABI (32-bit), generating a backtrace for execution contexts which
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@ -174,6 +174,9 @@
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/* Define to 1 if STT_GNU_IFUNC support actually works. */
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#define HAVE_IFUNC 0
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/* Define if gcc supports attribute ifunc. */
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#undef HAVE_GCC_IFUNC
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/* Define if the linker defines __ehdr_start. */
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#undef HAVE_EHDR_START
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42
configure
vendored
42
configure
vendored
@ -3916,6 +3916,36 @@ fi
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{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_ld_gnu_indirect_function" >&5
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$as_echo "$libc_cv_ld_gnu_indirect_function" >&6; }
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# Check if gcc supports attribute ifunc as it is used in libc_ifunc macro.
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{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for gcc attribute ifunc support" >&5
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$as_echo_n "checking for gcc attribute ifunc support... " >&6; }
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if ${libc_cv_gcc_indirect_function+:} false; then :
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$as_echo_n "(cached) " >&6
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else
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cat > conftest.c <<EOF
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extern int func (int);
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int used_func (int a)
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{
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return a;
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}
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static void *resolver ()
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{
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return &used_func;
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}
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extern __typeof (func) func __attribute__ ((ifunc ("resolver")));
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EOF
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libc_cv_gcc_indirect_function=no
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if ${CC-cc} -c conftest.c -o conftest.o 1>&5 \
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2>&5 ; then
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if $READELF -s conftest.o | grep IFUNC >/dev/null 2>&5; then
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libc_cv_gcc_indirect_function=yes
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fi
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fi
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rm -f conftest*
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fi
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{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gcc_indirect_function" >&5
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$as_echo "$libc_cv_gcc_indirect_function" >&6; }
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if test x"$libc_cv_ld_gnu_indirect_function" != xyes; then
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if test x"$multi_arch" = xyes; then
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as_fn_error $? "--enable-multi-arch support requires assembler and linker support" "$LINENO" 5
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@ -3923,6 +3953,13 @@ if test x"$libc_cv_ld_gnu_indirect_function" != xyes; then
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multi_arch=no
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fi
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fi
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if test x"$libc_cv_gcc_indirect_function" != xyes &&
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test x"$multi_arch" = xyes; then
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{ $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: --enable-multi-arch support recommends a gcc with gnu-indirect-function support.
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Please use a gcc which supports it by default or configure gcc with --enable-gnu-indirect-function" >&5
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$as_echo "$as_me: WARNING: --enable-multi-arch support recommends a gcc with gnu-indirect-function support.
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Please use a gcc which supports it by default or configure gcc with --enable-gnu-indirect-function" >&2;}
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fi
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multi_arch_d=
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if test x"$multi_arch" != xno; then
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multi_arch_d=/multiarch
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@ -6518,6 +6555,11 @@ if test x"$libc_cv_ld_gnu_indirect_function" = xyes; then
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fi
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if test x"$libc_cv_gcc_indirect_function" = xyes; then
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$as_echo "#define HAVE_GCC_IFUNC 1" >>confdefs.h
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fi
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# This is far from the AC_ARG_ENABLE that sets it so that a sysdeps
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# configure fragment can override the value to prevent this AC_DEFINE.
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33
configure.ac
33
configure.ac
@ -634,6 +634,30 @@ if ${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS \
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fi
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rm -f conftest*])
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# Check if gcc supports attribute ifunc as it is used in libc_ifunc macro.
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AC_CACHE_CHECK([for gcc attribute ifunc support],
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libc_cv_gcc_indirect_function, [dnl
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cat > conftest.c <<EOF
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extern int func (int);
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int used_func (int a)
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{
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return a;
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}
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static void *resolver ()
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{
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return &used_func;
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}
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extern __typeof (func) func __attribute__ ((ifunc ("resolver")));
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EOF
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libc_cv_gcc_indirect_function=no
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if ${CC-cc} -c conftest.c -o conftest.o 1>&AS_MESSAGE_LOG_FD \
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2>&AS_MESSAGE_LOG_FD ; then
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if $READELF -s conftest.o | grep IFUNC >/dev/null 2>&AS_MESSAGE_LOG_FD; then
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libc_cv_gcc_indirect_function=yes
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fi
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fi
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rm -f conftest*])
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if test x"$libc_cv_ld_gnu_indirect_function" != xyes; then
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if test x"$multi_arch" = xyes; then
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AC_MSG_ERROR([--enable-multi-arch support requires assembler and linker support])
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@ -641,6 +665,11 @@ if test x"$libc_cv_ld_gnu_indirect_function" != xyes; then
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multi_arch=no
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fi
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fi
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if test x"$libc_cv_gcc_indirect_function" != xyes &&
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test x"$multi_arch" = xyes; then
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AC_MSG_WARN([--enable-multi-arch support recommends a gcc with gnu-indirect-function support.
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Please use a gcc which supports it by default or configure gcc with --enable-gnu-indirect-function])
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fi
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multi_arch_d=
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if test x"$multi_arch" != xno; then
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multi_arch_d=/multiarch
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@ -1782,6 +1811,10 @@ if test x"$libc_cv_ld_gnu_indirect_function" = xyes; then
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AC_DEFINE(HAVE_IFUNC)
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fi
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if test x"$libc_cv_gcc_indirect_function" = xyes; then
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AC_DEFINE(HAVE_GCC_IFUNC)
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fi
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# This is far from the AC_ARG_ENABLE that sets it so that a sysdeps
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# configure fragment can override the value to prevent this AC_DEFINE.
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AC_SUBST(use_nscd)
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@ -402,6 +402,14 @@ the newest version of the compiler that is known to work for building
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release time, GCC 5.3 is the newest compiler verified to work to build
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@theglibc{}.
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For multi-arch support it is recommended to use a GCC which has been built with
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support for GNU indirect functions. This ensures that correct debugging
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information is generated for functions selected by IFUNC resolvers. This
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support can either be enabled by configuring GCC with
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@samp{--enable-gnu-indirect-function}, or by enabling it by default by setting
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@samp{default_gnu_indirect_function} variable for a particular architecture in
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the GCC source file @file{gcc/config.gcc}.
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You can use whatever compiler you like to compile programs that use
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@theglibc{}.
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