Re: [RFC] pb unwinding from pthread_cond_wait on ppc-linux (RFA?)

[Joel Brobecker <brobecker@adacore.com>]

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> Precisely!  That's what I thought it would be.  It's trying to load lr
> with the address of @+16, so that the function can access PIC data
> using PC-relative displacement.

Daniel, you never stop to impress me.

> (Does this obsolete the "branch in first three insns" check?  I'm not
> sure if there are other possible reasons for that.)

Here is a new patch that implements your suggestion. Indeed, I could
then remove the "branch in first three insns" check...

2004-12-09  Joel Brobecker  <brobecker@gnat.com>

        * rs6000-tdep.c (bl_to_blrl_insn_p): New function.
        (skip_prologue): Stop unconditionaly skipping "bl" instructions
        that are within the first 3 instruction. Instead, Skip that "bl"
        instruction iff the destination instruction is a "blrl".

Tested on powerpc-linux. No regression.

How does it look?

-- 
Joel

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Index: rs6000-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/rs6000-tdep.c,v
retrieving revision 1.233
diff -u -p -r1.233 rs6000-tdep.c
--- rs6000-tdep.c	25 Nov 2004 02:48:27 -0000	1.233
+++ rs6000-tdep.c	9 Dec 2004 15:40:46 -0000
@@ -823,6 +823,30 @@ store_param_on_stack_p (unsigned long op
   return 0;
 }
 
+/* Assuming that INSN is a "bl" instruction located at PC, return
+   nonzero if the destination of the branch is a "blrl" instruction.
+   
+   This sequence is sometimes found in certain function prologues.
+   It allows the function to load the LR register with a value that
+   they can use to access PIC data using PC-relative offsets.  */
+
+static int
+bl_to_blrl_insn_p (CORE_ADDR pc, int insn)
+{
+  const int opcode = 18;
+  const CORE_ADDR dest = branch_dest (opcode, insn, pc, -1);
+  int dest_insn;
+
+  if (dest == -1)
+    return 0;  /* Should never happen, but just return zero to be safe.  */
+  
+  dest_insn = read_memory_integer (dest, 4);
+  if ((dest_insn & 0xfc00ffff) == 0x4c000021) /* blrl */
+    return 1;
+
+  return 0;
+}
+
 static CORE_ADDR
 skip_prologue (CORE_ADDR pc, CORE_ADDR lim_pc, struct rs6000_framedata *fdata)
 {
@@ -1047,19 +1071,9 @@ skip_prologue (CORE_ADDR pc, CORE_ADDR l
 				   to save fprs??? */
 
 	  fdata->frameless = 0;
-	  /* Don't skip over the subroutine call if it is not within
-	     the first three instructions of the prologue and either
-	     we have no line table information or the line info tells
-	     us that the subroutine call is not part of the line
-	     associated with the prologue.  */
-	  if ((pc - orig_pc) > 8)
-	    {
-	      struct symtab_and_line prologue_sal = find_pc_line (orig_pc, 0);
-	      struct symtab_and_line this_sal = find_pc_line (pc, 0);
 
-	      if ((prologue_sal.line == 0) || (prologue_sal.line != this_sal.line))
-		break;
-	    }
+          if (bl_to_blrl_insn_p (pc, op))
+            continue;
 
 	  op = read_memory_integer (pc + 4, 4);