# 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 ...

# 

diff -urN glibc-2.17-c758a686/elf/elf.h glibc-2.17-c758a686/elf/elf.h

--- glibc-2.17-c758a686/elf/elf.h	2014-05-29 14:08:44.000000000 -0500

+++ glibc-2.17-c758a686/elf/elf.h	2014-05-29 14:08:44.000000000 -0500

@@ -2273,8 +2273,19 @@

 #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 */

diff -urN glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/dl-machine.h glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/dl-machine.h

--- glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/dl-machine.h	2014-05-29 14:08:40.000000000 -0500

+++ glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/dl-machine.h	2014-05-29 14:08:44.000000000 -0500

@@ -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

diff -urN glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/dl-trampoline.S glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/dl-trampoline.S

--- glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/dl-trampoline.S	2014-05-29 14:08:40.000000000 -0500

+++ glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/dl-trampoline.S	2014-05-29 14:08:44.000000000 -0500

@@ -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)