From 122b66defdb9e4ded3ccc5c2b290f0520c6fa3cd Mon Sep 17 00:00:00 2001 From: Ulrich Weigand Date: Wed, 4 Dec 2013 06:52:40 -0600 Subject: [PATCH] PowerPC64 ELFv2 ABI 3/6: PLT local entry point optimization This is a follow-on to the previous patch to support the ELFv2 ABI in the dynamic loader, split off into its own patch since it is just an optional optimization. In the ELFv2 ABI, most functions define both a global and a local entry point; the local entry requires r2 to be already set up by the caller to point to the callee's TOC; while the global entry does not require the caller to know about the callee's TOC, but it needs to set up r12 to the callee's entry point address. Now, when setting up a PLT slot, the dynamic linker will usually need to enter the target function's global entry point. However, if the linker can prove that the target function is in the same DSO as the PLT slot itself, and the whole DSO only uses a single TOC (which the linker will let ld.so know via a DT_PPC64_OPT entry), then it is possible to actually enter the local entry point address into the PLT slot, for a slight improvement in performance. Note that this uncovered a problem on the first call via _dl_runtime_resolve, because that routine neglected to restore the caller's TOC before calling the target function for the first time, since it assumed that function would always reload its own TOC anyway ... --- ChangeLog | 17 +++++++++ elf/elf.h | 11 ++++++ sysdeps/powerpc/powerpc64/dl-machine.h | 44 +++++++++++++++++++++-- sysdeps/powerpc/powerpc64/dl-trampoline.S | 8 +++++ 4 files changed, 78 insertions(+), 2 deletions(-) diff --git a/ChangeLog b/ChangeLog index d229f33151..668fe03d2b 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,20 @@ +2013-12-04 Ulrich Weigand + Alan Modra + + * elf/elf.h (DT_PPC64_OPT, PPC64_OPT_TLS, PPC64_OPT_MULTI_TOC): + Define. + (STO_PPC64_LOCAL_BIT, STO_PPC64_LOCAL_MASK, + PPC64_LOCAL_ENTRY_OFFSET): Define. + * sysdeps/powerpc/powerpc64/dl-machine.h (ppc64_local_entry_offset): + New function. + (elf_machine_fixup_plt): Call it. + (elf_machine_plt_conflict): Likewise. Add map, sym_map, and + reloc arguments. + (elf_machine_rela): Update call to elf_machine_plt_conflict. + * sysdeps/powerpc/powerpc64/dl-trampoline.S (_dl_runtime_resolve, + _dl_profile_resolve) [_CALL_ELF == 2]: Restore caller's TOC into + r2 before calling target. + 2013-12-04 Ulrich Weigand Alan Modra diff --git a/elf/elf.h b/elf/elf.h index 7a9855c850..08b4ed8893 100644 --- a/elf/elf.h +++ b/elf/elf.h @@ -2282,8 +2282,19 @@ typedef Elf32_Addr Elf32_Conflict; #define DT_PPC64_GLINK (DT_LOPROC + 0) #define DT_PPC64_OPD (DT_LOPROC + 1) #define DT_PPC64_OPDSZ (DT_LOPROC + 2) +#define DT_PPC64_OPT (DT_LOPROC + 3) #define DT_PPC64_NUM 3 +/* PowerPC64 specific values for the DT_PPC64_OPT Dyn entry. */ +#define PPC64_OPT_TLS 1 +#define PPC64_OPT_MULTI_TOC 2 + +/* PowerPC64 specific values for the Elf64_Sym st_other field. */ +#define STO_PPC64_LOCAL_BIT 5 +#define STO_PPC64_LOCAL_MASK (7 << STO_PPC64_LOCAL_BIT) +#define PPC64_LOCAL_ENTRY_OFFSET(other) \ + (((1 << (((other) & STO_PPC64_LOCAL_MASK) >> STO_PPC64_LOCAL_BIT)) >> 2) << 2) + /* ARM specific declarations */ diff --git a/sysdeps/powerpc/powerpc64/dl-machine.h b/sysdeps/powerpc/powerpc64/dl-machine.h index f222bb07d7..eccfbb3563 100644 --- a/sysdeps/powerpc/powerpc64/dl-machine.h +++ b/sysdeps/powerpc/powerpc64/dl-machine.h @@ -424,6 +424,42 @@ elf_machine_runtime_setup (struct link_map *map, int lazy, int profile) return lazy; } +#if _CALL_ELF == 2 +/* If the PLT entry whose reloc is 'reloc' resolves to a function in + the same object, return the target function's local entry point + offset if usable. */ +static inline Elf64_Addr __attribute__ ((always_inline)) +ppc64_local_entry_offset (struct link_map *map, lookup_t sym_map, + const Elf64_Rela *reloc) +{ + const Elf64_Sym *symtab; + const Elf64_Sym *sym; + + /* If the target function is in a different object, we cannot + use the local entry point. */ + if (sym_map != map) + return 0; + + /* If the linker inserted multiple TOCs, we cannot use the + local entry point. */ + if (map->l_info[DT_PPC64(OPT)] + && (map->l_info[DT_PPC64(OPT)]->d_un.d_val & PPC64_OPT_MULTI_TOC)) + return 0; + + /* Otherwise, we can use the local entry point. Retrieve its offset + from the symbol's ELF st_other field. */ + symtab = (const void *) D_PTR (map, l_info[DT_SYMTAB]); + sym = &symtab[ELFW(R_SYM) (reloc->r_info)]; + + /* If the target function is an ifunc then the local entry offset is + for the resolver, not the final destination. */ + if (__builtin_expect (ELFW(ST_TYPE) (sym->st_info) == STT_GNU_IFUNC, 0)) + return 0; + + return PPC64_LOCAL_ENTRY_OFFSET (sym->st_other); +} +#endif + /* Change the PLT entry whose reloc is 'reloc' to call the actual routine. */ static inline Elf64_Addr __attribute__ ((always_inline)) @@ -470,6 +506,7 @@ elf_machine_fixup_plt (struct link_map *map, lookup_t sym_map, PPC_DCBST (&plt->fd_func); PPC_ISYNC; #else + finaladdr += ppc64_local_entry_offset (map, sym_map, reloc); *reloc_addr = finaladdr; #endif @@ -477,7 +514,9 @@ elf_machine_fixup_plt (struct link_map *map, lookup_t sym_map, } static inline void __attribute__ ((always_inline)) -elf_machine_plt_conflict (Elf64_Addr *reloc_addr, Elf64_Addr finaladdr) +elf_machine_plt_conflict (struct link_map *map, lookup_t sym_map, + const Elf64_Rela *reloc, + Elf64_Addr *reloc_addr, Elf64_Addr finaladdr) { #if _CALL_ELF != 2 Elf64_FuncDesc *plt = (Elf64_FuncDesc *) reloc_addr; @@ -491,6 +530,7 @@ elf_machine_plt_conflict (Elf64_Addr *reloc_addr, Elf64_Addr finaladdr) PPC_DCBST (&plt->fd_toc); PPC_SYNC; #else + finaladdr += ppc64_local_entry_offset (map, sym_map, reloc); *reloc_addr = finaladdr; #endif } @@ -646,7 +686,7 @@ elf_machine_rela (struct link_map *map, /* Fall thru */ case R_PPC64_JMP_SLOT: #ifdef RESOLVE_CONFLICT_FIND_MAP - elf_machine_plt_conflict (reloc_addr, value); + elf_machine_plt_conflict (map, sym_map, reloc, reloc_addr, value); #else elf_machine_fixup_plt (map, sym_map, reloc, reloc_addr, value); #endif diff --git a/sysdeps/powerpc/powerpc64/dl-trampoline.S b/sysdeps/powerpc/powerpc64/dl-trampoline.S index bffc4cbab6..e31311cf18 100644 --- a/sysdeps/powerpc/powerpc64/dl-trampoline.S +++ b/sysdeps/powerpc/powerpc64/dl-trampoline.S @@ -74,6 +74,10 @@ EALIGN(_dl_runtime_resolve, 4, 0) /* Prepare for calling the function returned by fixup. */ PPC64_LOAD_FUNCPTR r3 ld r3,INT_PARMS+0(r1) +#if _CALL_ELF == 2 +/* Restore the caller's TOC in case we jump to a local entry point. */ + ld r2,FRAME_SIZE+40(r1) +#endif /* Unwind the stack frame, and jump. */ addi r1,r1,FRAME_SIZE bctr @@ -321,6 +325,10 @@ L(restoreFXR): /* Prepare for calling the function returned by fixup. */ PPC64_LOAD_FUNCPTR r3 ld r3,INT_PARMS+0(r1) +#if _CALL_ELF == 2 +/* Restore the caller's TOC in case we jump to a local entry point. */ + ld r2,FRAME_SIZE+40(r1) +#endif /* Load the floating point registers. */ lfd fp1,FPR_PARMS+0(r1) lfd fp2,FPR_PARMS+8(r1)