This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
[PATCH] [BZ #18422] elf/tst-audit tests fail without PLT entries
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: GNU C Library <libc-alpha at sourceware dot org>
- Date: Sat, 23 May 2015 06:14:08 -0700
- Subject: [PATCH] [BZ #18422] elf/tst-audit tests fail without PLT entries
- Authentication-results: sourceware.org; auth=none
PLT entries aren't required when -z now used. Linker on master with:
commit 25070364b0ce33eed46aa5d78ebebbec6accec7e
Author: H.J. Lu <hjl.tools@gmail.com>
Date: Sat May 16 07:00:21 2015 -0700
Don't generate PLT relocations for now binding
There is no need for PLT relocations with -z now. We can use GOT
relocations, which take less space, instead and replace 16-byte .plt
entres with 8-byte .plt.got entries.
bfd/
* elf32-i386.c (elf_i386_check_relocs): Create .plt.got section
for now binding.
(elf_i386_allocate_dynrelocs): Use .plt.got section for now
binding.
* elf64-x86-64.c (elf_x86_64_check_relocs): Create .plt.got
section for now binding.
(elf_x86_64_allocate_dynrelocs): Use .plt.got section for now
binding.
won't generate PLT entries with -z now. elf/tst-audit2.c has
/* This calloc definition will be called by the dynamic linker itself.
We test that it has initialized our TLS block by the time it does so.
*/
void *
calloc (size_t n, size_t m)
{
if (magic[0] != MAGIC1 || magic[1] != MAGIC2)
{
printf ("{%x, %x} != {%x, %x}\n", magic[0], magic[1], MAGIC1, MAGIC2);
abort ();
}
magic[0] = MAGIC2;
magic[1] = MAGIC1;
Since ld.so is built with -z now, there are no PLT relocations and this
calloc won't be used:
Relocation section '.rela.dyn' at offset 0x66c contains 16 entries:
Offset Info Type Sym.Value Sym. Name + Addend
00222e88 00000008 R_X86_64_RELATIVE 10970
00222e8c 00000008 R_X86_64_RELATIVE f8f0
00222e90 00000008 R_X86_64_RELATIVE f6c0
00222e94 00000008 R_X86_64_RELATIVE 11bd0
00222e98 00000008 R_X86_64_RELATIVE a1b0
00222e9c 00000008 R_X86_64_RELATIVE 130c0
00222ea0 00000008 R_X86_64_RELATIVE 13c50
00222ea4 00000008 R_X86_64_RELATIVE 15fc0
00222ea8 00000008 R_X86_64_RELATIVE 12cd0
00222eac 00000008 R_X86_64_RELATIVE 17f90
00222fbc 00000a06 R_X86_64_GLOB_DAT 00018230 __libc_memalign@@GLIBC_2.16 + 0
00222fc4 00001506 R_X86_64_GLOB_DAT 00018300 malloc@@GLIBC_2.16 + 0
00222fcc 00000d06 R_X86_64_GLOB_DAT 00018310 calloc@@GLIBC_2.16 + 0
00222fd4 00000506 R_X86_64_GLOB_DAT 000184a0 realloc@@GLIBC_2.16 + 0
00222fdc 00000706 R_X86_64_GLOB_DAT 002239a0 _r_debug@@GLIBC_2.16 + 0
00222fe4 00000406 R_X86_64_GLOB_DAT 00018340 free@@GLIBC_2.16 + 0
Assuming we do want to keep PLT relocations in ld.so so that malloc
functions in ld.so can be overridden, ld.so should be built with -z now.
There is no reason to build ld.so with -z now since ld.so is the one
doing BIND_NOW. The only thing we get with -z now on ld.so is DT tag:
0x0000000000000018 (BIND_NOW)
0x000000006ffffffb (FLAGS_1) Flags: NOW
This patch removes -Wl,-z,now from ld.so build.
OK for master?
H.J.
[BZ #18422]
* elf/Makefile (z-now-yes): Removed.
($(objpfx)ld.so): Remove $(z-now-$(bind-now)).
---
elf/Makefile | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/elf/Makefile b/elf/Makefile
index 34450ea..324b4a2 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -349,13 +349,11 @@ $(objpfx)librtld.os: $(objpfx)dl-allobjs.os $(objpfx)rtld-libc.a
generated += librtld.map librtld.mk rtld-libc.a librtld.os.map
-z-now-yes = -Wl,-z,now
-
$(objpfx)ld.so: $(objpfx)librtld.os $(ld-map)
# Link into a temporary file so that we don't touch $@ at all
# if the sanity check below fails.
$(LINK.o) -nostdlib -nostartfiles -shared -o $@.new \
- $(LDFLAGS-rtld) -Wl,-z,defs $(z-now-$(bind-now)) \
+ $(LDFLAGS-rtld) -Wl,-z,defs \
$(filter-out $(map-file),$^) $(load-map-file) \
-Wl,-soname=$(rtld-installed-name) \
-Wl,-defsym=_begin=0
--
2.1.0