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elf: Unconditionally use __ehdr_start

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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 <szabolcs.nagy@arm.com>
This commit is contained in:
Fangrui Song 2021-08-10 11:04:56 -07:00
parent 13710e7e6a
commit 302247c891
4 changed files with 4 additions and 98 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

3
config.h.in
View file

@ -198,9 +198,6 @@
/* Define if CC supports attribute retain. */
#undef HAVE_GNU_RETAIN
/* Define if the linker defines __ehdr_start. */
#undef HAVE_EHDR_START
/* Define to 1 if the assembler needs intermediate aliases to define
multiple symbol versions for one symbol. */
#define SYMVER_NEEDS_ALIAS 0

52
configure vendored
View file

@ -6636,58 +6636,6 @@ 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 whether the assembler requires one version per symbol" >&5
$as_echo_n "checking whether the assembler requires one version per symbol... " >&6; }
if ${libc_cv_symver_needs_alias+:} false; then :

34
configure.ac
View file

@ -1662,40 +1662,6 @@ 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
dnl Starting with binutils 2.35, GAS can attach multiple symbol versions
dnl to one symbol (PR 23840).
AC_CACHE_CHECK(whether the assembler requires one version per symbol,

13
elf/rtld.c
View file

@ -1684,21 +1684,16 @@ dl_main (const ElfW(Phdr) *phdr,
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)));