sparc: Use ba,a,pt in PLTs and fix bugs in R_SPARC_JMP_IREL handling.

2010-03-03  David S. Miller  <davem@davemloft.net>

	* sysdeps/sparc/sparc32/dl-machine.h (elf_machine_lazy_rel): Must
	pass '1' for 't' argument to sparc_fixup_plt.
	* sysdeps/sparc/sparc64/dl-machine.h (elf_machine_lazy_rel):
	Likewise.
	* sysdeps/sparc/sparc32/dl-plt.h (OPCODE_BA_PT): Define.
	(sparc_fixup_plt): Document 't' argument.  Enable branch
	optimization and use v9 branches when possible.  Explain why we
	cannot unconditionally patch the branch into the first PLT
	instruction.
	* sysdeps/sparc/sparc64/dl-plt.h (sparc64_fixup_plt): Document 't'
	argument.  Use v9 branches when possible.  Explain why we can in
	fact unconditionally use a branch in the first PLT instruction
	here.

1 files changed, 41 insertions, 6 deletions

diff --git a/sysdeps/sparc/sparc32/dl-plt.h b/sysdeps/sparc/sparc32/dl-plt.h
index edcc5c1374..bfb891fe69 100644
--- a/sysdeps/sparc/sparc32/dl-plt.h
+++ b/sysdeps/sparc/sparc32/dl-plt.h
@@ -25,19 +25,55 @@
 #define OPCODE_JMP_G1	0x81c06000 /* jmp %g1+?; add lo 10 bits of value */
 #define OPCODE_SAVE_SP	0x9de3bfa8 /* save %sp, -(16+6)*4, %sp */
 #define OPCODE_BA	0x30800000 /* b,a ?; add PC-rel word address */
+#define OPCODE_BA_PT	0x30480000 /* ba,a,pt %icc, ?; add PC-rel word address */
 
 static inline __attribute__ ((always_inline)) Elf32_Addr
 sparc_fixup_plt (const Elf32_Rela *reloc, Elf32_Addr *reloc_addr,
 		 Elf32_Addr value, int t, int do_flush)
 {
-  Elf32_Sword disp = value - (Elf32_Addr) reloc_addr;
+  Elf32_Sword disp;
 
-  if (0 && disp >= -0x800000 && disp < 0x800000)
+  /* 't' is '0' if we are resolving this PLT entry for RTLD bootstrap,
+     in which case we'll be resolving all PLT entries and thus can
+     optimize by overwriting instructions starting at the first PLT entry
+     instruction and we need not be mindful of thread safety.
+
+     Otherwise, 't' is '1'.  */
+  reloc_addr += t;
+  disp = value - (Elf32_Addr) reloc_addr;
+
+  if (disp >= -0x800000 && disp < 0x800000)
     {
-      /* Don't need to worry about thread safety. We're writing just one
-	 instruction.  */
+      unsigned int insn = OPCODE_BA | ((disp >> 2) & 0x3fffff);
+
+#ifdef __sparc_v9__
+      /* On V9 we can do even better by using a branch with
+	 prediction if we fit into the even smaller 19-bit
+	 displacement field.  */
+      if (disp >= -0x100000 && disp < 0x100000)
+	insn = OPCODE_BA_PT | ((disp >> 2) & 0x07ffff);
+#endif
+
+      /* Even if we are writing just a single branch, we must not
+	 ignore the 't' offset.  Consider a case where we have some
+	 PLT slots which can be optimized into a single branch and
+	 some which cannot.  Then we can end up with a PLT which looks
+	 like:
+
+		PLT4.0: sethi	%(PLT_4_INDEX), %g1
+			sethi	%(fully_resolved_sym_4), %g1
+			jmp	%g1 + %lo(fully_resolved_sym_4)
+		PLT5.0:	ba,a	fully_resolved_sym_5
+			ba,a	PLT0.0
+			...
+
+	  The delay slot of that jmp must always be either a sethi to
+	  %g1 or a nop.  But if we try to place this displacement
+	  branch there, PLT4.0 will jump to fully_resolved_sym_4 for 1
+	  instruction and then go immediately to
+	  fully_resolved_sym_5.  */
 
-      reloc_addr[0] = OPCODE_BA | ((disp >> 2) & 0x3fffff);
+      reloc_addr[0] = insn;
       if (do_flush)
 	__asm __volatile ("flush %0" : : "r"(reloc_addr));
     }
@@ -48,7 +84,6 @@ sparc_fixup_plt (const Elf32_Rela *reloc, Elf32_Addr *reloc_addr,
 	 need not be done during bootstrapping, since there are no threads.
 	 But we also can't tell if we _can_ use flush, so don't. */
 
-      reloc_addr += t;
       reloc_addr[1] = OPCODE_JMP_G1 | (value & 0x3ff);
       if (do_flush)
 	__asm __volatile ("flush %0+4" : : "r"(reloc_addr));