diff options
| author | Alan Modra <amodra@gmail.com> | 2022-01-22 11:48:50 +1030 |
|---|---|---|
| committer | Alan Modra <amodra@gmail.com> | 2022-04-10 08:33:06 +0930 |
| commit | d6efcc118e406a1cfeb309f835d7118df53419bb (patch) | |
| tree | 31bbfdb82f662a47fece23a2e7f1324ea0c3ce6e /sysdeps/powerpc/powerpc64/dl-machine.h | |
| parent | 30afd8c44d6a0a8b0eddbadecb02c9b9dad3facf (diff) | |
| download | glibc-d6efcc118e406a1cfeb309f835d7118df53419bb.tar glibc-d6efcc118e406a1cfeb309f835d7118df53419bb.tar.gz glibc-d6efcc118e406a1cfeb309f835d7118df53419bb.tar.bz2 glibc-d6efcc118e406a1cfeb309f835d7118df53419bb.zip | |
powerpc64: Use medium model toc accesses throughout
The PowerPC64 linker edits medium model toc-indirect code to toc-pointer
relative:
addis r9,r2,tc_entry_for_var@toc@ha
ld r9,tc_entry_for_var@toc@l(r9)
becomes
addis r9,r2,(var-.TOC.)@ha
addi r9,r9,(var-.TOC.)@l
when "var" is known to be local to the binary. This isn't done for
small-model toc-indirect code, because "var" is almost guaranteed to
be too far away from .TOC. for a 16-bit signed offset. And, because
the analysis of which .toc entry can be removed becomes much more
complicated in objects that mix code models, they aren't removed if
any small-model toc sequence appears in an object file.
Unfortunately, glibc's build of ld.so smashes the needed objects
together in a ld -r linking stage. This means the GOT/TOC is left
with a whole lot of relative relocations which is untidy, but in
itself is not a serious problem. However, static-pie on powerpc64
bombs due to a segfault caused by one of the small-model accesses
before _dl_relocate_static_pie. (The very first one in rcrt1.o
passing start_addresses in r8 to __libc_start_main.)
So this patch makes all the toc/got accesses in assembly medium code
model, and a couple of functions hidden. By itself this is not
enough to give us working static-pie, but it is useful in isolation to
enable better linker optimisation.
There's a serious problem in libgcc too. libgcc ifuncs access the
AT_HWCAP words stored in the tcb with an offset from the thread
pointer (r13), but r13 isn't set at the time _dl_relocate_static_pie.
A followup patch will fix that.
Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>
Diffstat (limited to 'sysdeps/powerpc/powerpc64/dl-machine.h')
| -rw-r--r-- | sysdeps/powerpc/powerpc64/dl-machine.h | 12 |
1 files changed, 8 insertions, 4 deletions
diff --git a/sysdeps/powerpc/powerpc64/dl-machine.h b/sysdeps/powerpc/powerpc64/dl-machine.h index 5da5de7a0a..6fab5cbe81 100644 --- a/sysdeps/powerpc/powerpc64/dl-machine.h +++ b/sysdeps/powerpc/powerpc64/dl-machine.h @@ -175,9 +175,12 @@ BODY_PREFIX "_dl_start_user:\n" \ /* the address of _start in r30. */ \ " mr 30,3\n" \ /* &_dl_argc in 29, &_dl_argv in 27, and _dl_loaded in 28. */ \ -" ld 28,.LC__rtld_local@toc(2)\n" \ -" ld 29,.LC__dl_argc@toc(2)\n" \ -" ld 27,.LC__dl_argv@toc(2)\n" \ +" addis 28,2,.LC__rtld_local@toc@ha\n" \ +" ld 28,.LC__rtld_local@toc@l(28)\n" \ +" addis 29,2,.LC__dl_argc@toc@ha\n" \ +" ld 29,.LC__dl_argc@toc@l(29)\n" \ +" addis 27,2,.LC__dl_argv@toc@ha\n" \ +" ld 27,.LC__dl_argv@toc@l(27)\n" \ /* _dl_init (_dl_loaded, _dl_argc, _dl_argv, _dl_argv+_dl_argc+1). */ \ " ld 3,0(28)\n" \ " lwa 4,0(29)\n" \ @@ -204,7 +207,8 @@ BODY_PREFIX "_dl_start_user:\n" \ " addi 6,6,8\n" \ /* Pass a termination function pointer (in this case _dl_fini) in \ r7. */ \ -" ld 7,.LC__dl_fini@toc(2)\n" \ +" addis 7,2,.LC__dl_fini@toc@ha\n" \ +" ld 7,.LC__dl_fini@toc@l(7)\n" \ /* Pass the stack pointer in r1 (so far so good), pointing to a NULL \ value. This lets our startup code distinguish between a program \ linked statically, which linux will call with argc on top of the \ |