[rfa/ppc] prologue parser tweaks

[Andrew Cagney <cagney@gnu.org>]

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Hello,

Attached are two tweaks to the PPC skip_prologue method so that it works 
better with glibc:

- handle glibc syscall
Without this an unwinder won't be able to find its way out of a system 
call - it needs to figure out the location of a local label, see comment 
for details.

- handle PIC code where the LR appears to be saved twice
It appears that skip_prologue code tried to handle this but missed an 
edge case.  Without this the wrong LR gets used when trying to unwind 
out of GLIBC.

Ok for mainline?

Andrew

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2004-03-07  Andrew Cagney  <cagney@redhat.com>

	* rs6000-tdep.c: Add field "func_start".
	(skip_prologue): New variable num_skip_syscall_insn, use to skip
	over first half of a GNU/Linux syscall and update "func_start".
	Record only the first LR save, use to skip over PIC code.

Index: rs6000-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/rs6000-tdep.c,v
retrieving revision 1.183
diff -u -r1.183 rs6000-tdep.c
--- rs6000-tdep.c	2 Mar 2004 02:20:25 -0000	1.183
+++ rs6000-tdep.c	16 Mar 2004 22:08:24 -0000
@@ -65,6 +65,7 @@
 
 struct rs6000_framedata
   {
+    CORE_ADDR func_start;	/* true function start */
     int offset;			/* total size of frame --- the distance
 				   by which we decrement sp to allocate
 				   the frame */
@@ -502,6 +503,7 @@
   int minimal_toc_loaded = 0;
   int prev_insn_was_prologue_insn = 1;
   int num_skip_non_prologue_insns = 0;
+  int num_skip_syscall_insn = 0;
   const struct bfd_arch_info *arch_info = gdbarch_bfd_arch_info (current_gdbarch);
   struct gdbarch_tdep *tdep = gdbarch_tdep (current_gdbarch);
   
@@ -521,6 +523,7 @@
     lim_pc = refine_prologue_limit (pc, lim_pc);
 
   memset (fdata, 0, sizeof (struct rs6000_framedata));
+  fdata->func_start = pc;
   fdata->saved_gpr = -1;
   fdata->saved_fpr = -1;
   fdata->saved_vr = -1;
@@ -548,6 +551,70 @@
       if (target_read_memory (pc, buf, 4))
 	break;
       op = extract_signed_integer (buf, 4);
+
+      /* A PPC64 GNU/Linux system call function starts with a
+	 non-threaded fast-path, only when that fails is a stack frame
+	 created, treat it as several functions:
+	 nptl/sysdeps/unix/sysv/linux/powerpc/powerpc32/sysdep-cancel.h
+
+	 *INDENT-OFF*
+	 NAME:
+	 	SINGLE_THREAD_P
+	 	bne- .Lpseudo_cancel
+	 __NAME_nocancel:
+	 	li r0,162
+	 	sc
+	 	bnslr+
+	 	b 0x7fe014ef64 <.__syscall_error>
+	 Lpseudo_cancel:
+	 	stdu r1,-128(r1)
+	 	...
+	 *INDENT-ON* */
+
+      if (((op & 0xffff0000) == 0x38000000 /* li r0,N */
+	   && pc == fdata->func_start + 0)
+	  || (op == 0x44000002 /* sc */
+	      && pc == fdata->func_start + 4
+	      && num_skip_syscall_insn == 1)
+	  || (op == 0x4ca30020 /* bnslr+ */
+	      && pc == fdata->func_start + 8
+	      && num_skip_syscall_insn == 2))
+	{
+	  num_skip_syscall_insn++;
+	  continue;
+	}
+      else if ((op & 0xfc000003) == 0x48000000 /* b __syscall_error */
+	       && pc == fdata->func_start + 12
+	       && num_skip_syscall_insn == 3)
+	{
+	  num_skip_syscall_insn++;
+	  fdata->func_start = pc;
+	  continue;
+	}
+
+      if ((op & 0xfc1fffff) == 0x7c0802a6)
+	{			/* mflr Rx */
+	  /* Since shared library / PIC code, which needs to get its
+	     address at runtime, can appear to save more than one link
+	     register vis:
+
+	     *INDENT-OFF*
+	     stwu r1,-304(r1)
+	     mflr r3
+	     bl 0xff570d0 (blrl)
+	     stw r30,296(r1)
+	     mflr r30
+	     stw r31,300(r1)
+	     stw r3,308(r1);
+	     ...
+	     *INDENT-ON*
+
+	     remember just the first one, but skip over additional
+	     ones.  */
+	  if (lr_reg < 0)
+	    lr_reg = (op & 0x03e00000);
+	  continue;
+	}
 
       if ((op & 0xfc1fffff) == 0x7c0802a6)
 	{			/* mflr Rx */