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GNU C Library master sources branch roland/ehdr_start created. glibc-2.19-141-g673dd44
- From: roland at sourceware dot org
- To: glibc-cvs at sourceware dot org
- Date: 11 Mar 2014 22:18:57 -0000
- Subject: GNU C Library master sources branch roland/ehdr_start created. glibc-2.19-141-g673dd44
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at 673dd446ab3bdd7c30569432955b10250781c13b (commit)
- Log -----------------------------------------------------------------
http://sourceware.org/git/gitweb.cgi?p=glibc.git;a=commitdiff;h=673dd446ab3bdd7c30569432955b10250781c13b
commit 673dd446ab3bdd7c30569432955b10250781c13b
Author: Roland McGrath <roland@hack.frob.com>
Date: Tue Mar 11 15:17:02 2014 -0700
Use __ehdr_start, when available, for rtld to get its own headers.
diff --git a/ChangeLog b/ChangeLog
index 3a589d8..cd57fbf 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
2014-03-11 Roland McGrath <roland@hack.frob.com>
+ * configure.ac (HAVE_EHDR_START): New check.
+ * configure: Regenerated.
+ * config.h.in (HAVE_EHDR_START): New #undef.
+ * elf/rtld.c (dl_main) [HAVE_EHDR_START]: Use __ehdr_start rather than
+ assuming the lowest-addressed segment maps the start of the file.
+
* sysdeps/arm/setjmp.S: Use sfi_breg on stores of mangled registers.
* sysdeps/arm/__longjmp.S: Use sfi_breg on loads of mangled registers.
Move sfi_sp use from the load-multiple (that no longer sets sp) to
diff --git a/config.h.in b/config.h.in
index 40797e7..ed3c593 100644
--- a/config.h.in
+++ b/config.h.in
@@ -195,6 +195,9 @@
/* Define if linux/fanotify.h is available. */
#undef HAVE_LINUX_FANOTIFY_H
+/* Define if the linker defines __ehdr_start. */
+#undef HAVE_EHDR_START
+
/*
*/
diff --git a/configure b/configure
index fc023d0..3ee1848 100755
--- a/configure
+++ b/configure
@@ -7268,6 +7268,44 @@ if test $libc_cv_predef_stack_protector = yes; then
fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the linker provides __ehdr_start" >&5
+$as_echo_n "checking whether the linker provides __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"
+LIBS=
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h. */
+
+extern const char __ehdr_start __attribute__ ((visibility ("hidden")));
+const char *ehdr (void) { return &__ehdr_start; }
+
+_ACEOF
+if ac_fn_c_try_link "$LINENO"; then :
+ libc_cv_ehdr_start=yes
+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
+
+fi
+
### End of automated tests.
### Now run sysdeps configure fragments.
diff --git a/configure.ac b/configure.ac
index f3dd87d..59dbb5e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2069,6 +2069,27 @@ if test $libc_cv_predef_stack_protector = yes; then
fi
AC_SUBST(libc_extra_cflags)
+AC_CACHE_CHECK([whether the linker provides __ehdr_start],
+ libc_cv_ehdr_start, [
+old_CFLAGS="$CFLAGS"
+old_LDFLAGS="$LDFLAGS"
+old_LIBS="$LIBS"
+CFLAGS="$CFLAGS -fPIC"
+LDFLAGS="$LDFLAGS -nostdlib -nostartfiles -shared"
+LIBS=
+AC_LINK_IFELSE([AC_LANG_SOURCE([
+extern const char __ehdr_start __attribute__ ((visibility ("hidden")));
+const char *ehdr (void) { return &__ehdr_start; }
+])],
+ [libc_cv_ehdr_start=yes], [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])
+fi
+
### End of automated tests.
### Now run sysdeps configure fragments.
diff --git a/elf/rtld.c b/elf/rtld.c
index 7f1413a..ae36a7a 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -1370,10 +1370,25 @@ of this helper program; chances are you did not intend to run this program.\n\
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. */
- ElfW(Ehdr) *rtld_ehdr = (ElfW(Ehdr) *) GL(dl_rtld_map).l_map_start;
- ElfW(Phdr) *rtld_phdr = (ElfW(Phdr) *) (GL(dl_rtld_map).l_map_start
- + rtld_ehdr->e_phoff);
+ 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
+ assert (rtld_ehdr->e_ehsize == sizeof *rtld_ehdr);
+ assert (rtld_ehdr->e_phentsize == sizeof (ElfW(Phdr)));
+
+ const ElfW(Phdr) *rtld_phdr = (const void *) rtld_ehdr + rtld_ehdr->e_phoff;
+
GL(dl_rtld_map).l_phdr = rtld_phdr;
GL(dl_rtld_map).l_phnum = rtld_ehdr->e_phnum;
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