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.
Alan Modra via Libc-alpha <libc-alpha@sourceware.org> writes:
> 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>
@@ -47,12 +47,14 @@
ENTRY (__longjmp)
CALL_MCOUNT 2
#ifndef __NO_VMX__
- ld r5,.LC__dl_hwcap@toc(r2)
+ addis r5,r2,.LC__dl_hwcap@toc@ha
+ ld r5,.LC__dl_hwcap@toc@l(r5)
# ifdef SHARED
/* Load _rtld-global._dl_hwcap. */
- ld r5,RTLD_GLOBAL_RO_DL_HWCAP_OFFSET(r5)
+ ld r5,RTLD_GLOBAL_RO_DL_HWCAP_OFFSET(r5)
# else
- ld r5,0(r5) /* Load extern _dl_hwcap. */
+ /* Load extern _dl_hwcap. */
+ ld r5,0(r5)
# endif
andis. r5,r5,(PPC_FEATURE_HAS_ALTIVEC >> 16)
beq L(no_vmx)
@@ -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 \
@@ -32,6 +32,7 @@
because gcc as of 2010/05 doesn't allocate a proper stack frame for
a function that makes no calls except for __tls_get_addr and we
might be here resolving the __tls_get_addr call. */
+ .hidden _dl_runtime_resolve
#define INT_PARMS FRAME_MIN_SIZE
ENTRY (_dl_runtime_resolve, 4)
stdu r1,-FRAME_SIZE(r1)
@@ -195,6 +196,7 @@ END(_dl_runtime_resolve)
parm1 (r3) and the index (r0) needs to be converted to an offset
(index * 24) in parm2 (r4). */
#ifndef PROF
+ .hidden _dl_profile_resolve
ENTRY (_dl_profile_resolve, 4)
/* Spill r30, r31 to preserve the link_map* and reloc_addr, in case we
need to call _dl_audit_pltexit. */
@@ -225,12 +227,14 @@ ENTRY (_dl_profile_resolve, 4)
std r9,INT_PARMS+48(r1)
std r10,INT_PARMS+56(r1)
std r8,CALLING_SP(r1)
- ld r12,.LC__dl_hwcap@toc(r2)
+ addis r12,r2,.LC__dl_hwcap@toc@ha
+ ld r12,.LC__dl_hwcap@toc@l(r12)
#ifdef SHARED
/* Load _rtld_local_ro._dl_hwcap. */
ld r12,RTLD_GLOBAL_RO_DL_HWCAP_OFFSET(r12)
#else
- ld r12,0(r12) /* Load extern _dl_hwcap. */
+ /* Load extern _dl_hwcap. */
+ ld r12,0(r12)
#endif
andis. r0,r12,(PPC_FEATURE_HAS_ALTIVEC >> 16)
beq L(saveFP)
@@ -132,12 +132,14 @@ JUMPTARGET(GLUE(__sigsetjmp_symbol,_ent)):
std r31,((JB_GPRS+17)*8)(3)
stfd fp31,((JB_FPRS+17)*8)(3)
#ifndef __NO_VMX__
- ld r6,.LC__dl_hwcap@toc(r2)
+ addis r6,r2,.LC__dl_hwcap@toc@ha
+ ld r6,.LC__dl_hwcap@toc@l(r6)
# ifdef SHARED
/* Load _rtld-global._dl_hwcap. */
- ld r6,RTLD_GLOBAL_RO_DL_HWCAP_OFFSET(r6)
+ ld r6,RTLD_GLOBAL_RO_DL_HWCAP_OFFSET(r6)
# else
- ld r6,0(r6) /* Load extern _dl_hwcap. */
+ /* Load extern _dl_hwcap. */
+ ld r6,0(r6)
# endif
andis. r6,r6,(PPC_FEATURE_HAS_ALTIVEC >> 16)
beq L(no_vmx)
@@ -74,7 +74,8 @@ ENTRY (_start)
/* put the address of start_addresses in r8... **
** PPC64 ABI uses R13 for thread local, so we leave it alone */
- ld r8,.L01@toc(r2)
+ addis r8,r2,.L01@toc@ha
+ ld r8,.L01@toc@l(r8)
/* and continue in libc-start, in glibc. */
b JUMPTARGET(__libc_start_main)
@@ -469,14 +469,16 @@ LT_LABELSUFFIX(name,_name_end): ; \
.tc _rtld_global_ro[TC],_rtld_global_ro
# endif
# define __GLRO(rOUT, var, offset) \
- ld rOUT,.LC__ ## var@toc(r2); \
+ addis rOUT,r2,.LC__ ## var@toc@ha; \
+ ld rOUT,.LC__ ## var@toc@l(rOUT); \
lwz rOUT,offset(rOUT)
#else
# define __GLRO_DEF(var) \
.LC__ ## var: \
.tc _ ## var[TC],_ ## var
# define __GLRO(rOUT, var, offset) \
- ld rOUT,.LC__ ## var@toc(r2); \
+ addis rOUT,r2,.LC__ ## var@toc@ha; \
+ ld rOUT,.LC__ ## var@toc@l(rOUT); \
lwz rOUT,0(rOUT)
#endif