From ec38ea9597b3c5ebcf71ff4d07a3ffc1c010bbee Mon Sep 17 00:00:00 2001 From: Fangrui Song Date: Thu, 26 Aug 2021 17:41:24 -0700 Subject: [PATCH] elf: Unconditionally use __ehdr_start We can consider __ehdr_start (from binutils 2.23 onwards) unconditionally supported, since configure.ac requires binutils>=2.25. The configure.ac check is related to an ia64 bug fixed by binutils 2.24. See https://sourceware.org/pipermail/libc-alpha/2014-August/053503.html Tested on x86_64-linux-gnu. Tested build-many-glibcs.py with aarch64-linux-gnu and s390x-linux-gnu. Reviewed-by: Szabolcs Nagy (cherry picked from commit 302247c89121e8d4c7629e589edbb4974fff6edb) --- config.h.in | 3 --- configure | 52 ---------------------------------------------------- configure.ac | 34 ---------------------------------- elf/rtld.c | 13 ++++--------- 4 files changed, 4 insertions(+), 98 deletions(-) diff --git a/config.h.in b/config.h.in index 9d0f5355ba..2aed757829 100644 --- a/config.h.in +++ b/config.h.in @@ -171,9 +171,6 @@ /* Define if gcc supports attribute ifunc. */ #undef HAVE_GCC_IFUNC -/* Define if the linker defines __ehdr_start. */ -#undef HAVE_EHDR_START - #define WANT_FLOAT128 0 /* diff --git a/configure b/configure index 9591958b46..f033eef082 100755 --- a/configure +++ b/configure @@ -6569,58 +6569,6 @@ if test $libc_cv_predef_fortify_source = yes; then fi -# Some linkers on some architectures support __ehdr_start but with -# bugs. Make sure usage of it does not create relocations in the -# output (as the linker should resolve them all for us). -{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the linker provides working __ehdr_start" >&5 -$as_echo_n "checking whether the linker provides working __ehdr_start... " >&6; } -if ${libc_cv_ehdr_start+:} false; then : - $as_echo_n "(cached) " >&6 -else - -old_CFLAGS="$CFLAGS" -old_LDFLAGS="$LDFLAGS" -old_LIBS="$LIBS" -CFLAGS="$CFLAGS -fPIC" -LDFLAGS="$LDFLAGS -nostdlib -nostartfiles -shared $no_ssp" -LIBS= -cat confdefs.h - <<_ACEOF >conftest.$ac_ext -/* end confdefs.h. */ - -typedef struct { - char foo; - long val; -} Ehdr; -extern const Ehdr __ehdr_start __attribute__ ((visibility ("hidden"))); -long ehdr (void) { return __ehdr_start.val; } - -_ACEOF -if ac_fn_c_try_link "$LINENO"; then : - if $READELF -r conftest | grep -F __ehdr_start >/dev/null; then - libc_cv_ehdr_start=broken - else - libc_cv_ehdr_start=yes - fi -else - libc_cv_ehdr_start=no -fi -rm -f core conftest.err conftest.$ac_objext \ - conftest$ac_exeext conftest.$ac_ext -CFLAGS="$old_CFLAGS" -LDFLAGS="$old_LDFLAGS" -LIBS="$old_LIBS" - -fi -{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_ehdr_start" >&5 -$as_echo "$libc_cv_ehdr_start" >&6; } -if test "$libc_cv_ehdr_start" = yes; then - $as_echo "#define HAVE_EHDR_START 1" >>confdefs.h - -elif test "$libc_cv_ehdr_start" = broken; then - { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: linker is broken -- you should upgrade" >&5 -$as_echo "$as_me: WARNING: linker is broken -- you should upgrade" >&2;} -fi - { $as_echo "$as_me:${as_lineno-$LINENO}: checking for __builtin_trap with no external dependencies" >&5 $as_echo_n "checking for __builtin_trap with no external dependencies... " >&6; } if ${libc_cv_builtin_trap+:} false; then : diff --git a/configure.ac b/configure.ac index cb6fb33ed9..6197321742 100644 --- a/configure.ac +++ b/configure.ac @@ -1665,40 +1665,6 @@ if test $libc_cv_predef_fortify_source = yes; then fi AC_SUBST(CPPUNDEFS) -# Some linkers on some architectures support __ehdr_start but with -# bugs. Make sure usage of it does not create relocations in the -# output (as the linker should resolve them all for us). -AC_CACHE_CHECK([whether the linker provides working __ehdr_start], - libc_cv_ehdr_start, [ -old_CFLAGS="$CFLAGS" -old_LDFLAGS="$LDFLAGS" -old_LIBS="$LIBS" -CFLAGS="$CFLAGS -fPIC" -LDFLAGS="$LDFLAGS -nostdlib -nostartfiles -shared $no_ssp" -LIBS= -AC_LINK_IFELSE([AC_LANG_SOURCE([ -typedef struct { - char foo; - long val; -} Ehdr; -extern const Ehdr __ehdr_start __attribute__ ((visibility ("hidden"))); -long ehdr (void) { return __ehdr_start.val; } -])], - [if $READELF -r conftest | grep -F __ehdr_start >/dev/null; then - libc_cv_ehdr_start=broken - else - libc_cv_ehdr_start=yes - fi], [libc_cv_ehdr_start=no]) -CFLAGS="$old_CFLAGS" -LDFLAGS="$old_LDFLAGS" -LIBS="$old_LIBS" -]) -if test "$libc_cv_ehdr_start" = yes; then - AC_DEFINE([HAVE_EHDR_START]) -elif test "$libc_cv_ehdr_start" = broken; then - AC_MSG_WARN([linker is broken -- you should upgrade]) -fi - AC_CACHE_CHECK(for __builtin_trap with no external dependencies, libc_cv_builtin_trap, [dnl libc_cv_builtin_trap=no diff --git a/elf/rtld.c b/elf/rtld.c index 498d9f5861..3b60b49fe9 100644 --- a/elf/rtld.c +++ b/elf/rtld.c @@ -1385,21 +1385,16 @@ of this helper program; chances are you did not intend to run this program.\n\ if (GLRO(dl_use_load_bias) == (ElfW(Addr)) -2) GLRO(dl_use_load_bias) = main_map->l_addr == 0 ? -1 : 0; - /* Set up the program header information for the dynamic linker - itself. It is needed in the dl_iterate_phdr callbacks. */ - const ElfW(Ehdr) *rtld_ehdr; - /* Starting from binutils-2.23, the linker will define the magic symbol __ehdr_start to point to our own ELF header if it is visible in a segment that also includes the phdrs. If that's not available, we use the old method that assumes the beginning of the file is part of the lowest-addressed PT_LOAD segment. */ -#ifdef HAVE_EHDR_START extern const ElfW(Ehdr) __ehdr_start __attribute__ ((visibility ("hidden"))); - rtld_ehdr = &__ehdr_start; -#else - rtld_ehdr = (void *) GL(dl_rtld_map).l_map_start; -#endif + + /* Set up the program header information for the dynamic linker + itself. It is needed in the dl_iterate_phdr callbacks. */ + const ElfW(Ehdr) *rtld_ehdr = &__ehdr_start; assert (rtld_ehdr->e_ehsize == sizeof *rtld_ehdr); assert (rtld_ehdr->e_phentsize == sizeof (ElfW(Phdr)));