# commit 122b66defdb9e4ded3ccc5c2b290f0520c6fa3cd
# Author: Ulrich Weigand <Ulrich.Weigand@de.ibm.com>
# Date:   Wed Dec 4 06:52:40 2013 -0600
# 
#     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 ...
# 
---
# elf/elf.h                                 |   11 +++++++
# sysdeps/powerpc/powerpc64/dl-machine.h    |   44 ++++++++++++++++++++++++++++--
# sysdeps/powerpc/powerpc64/dl-trampoline.S |    8 +++++
# 3 files changed, 61 insertions(+), 2 deletions(-)
#
--- a/elf/elf.h
+++ b/elf/elf.h
@@ -2270,8 +2270,19 @@
 #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 */
 
--- a/sysdeps/powerpc/powerpc64/dl-machine.h
+++ b/sysdeps/powerpc/powerpc64/dl-machine.h
@@ -425,6 +425,42 @@
   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))
@@ -471,6 +507,7 @@
   PPC_DCBST (&plt->fd_func);
   PPC_ISYNC;
 #else
+  finaladdr += ppc64_local_entry_offset (map, sym_map, reloc);
   *reloc_addr = finaladdr;
 #endif
 
@@ -478,7 +515,9 @@
 }
 
 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;
@@ -492,6 +531,7 @@
   PPC_DCBST (&plt->fd_toc);
   PPC_SYNC;
 #else
+  finaladdr += ppc64_local_entry_offset (map, sym_map, reloc);
   *reloc_addr = finaladdr;
 #endif
 }
@@ -641,7 +681,7 @@
       /* 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
--- a/sysdeps/powerpc/powerpc64/dl-trampoline.S
+++ b/sysdeps/powerpc/powerpc64/dl-trampoline.S
@@ -74,6 +74,10 @@
 /* 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 @@
 /* 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)
