Re: [PATCH] Fix PPC non-CFI + CFI unwinding (incomplete in HEAD)

Jan Kratochvil
2007-01-14T21:34:31Z

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On Sat, 13 Jan 2007 17:40:28 +0100, Daniel Jacobowitz wrote:
...
> I was thinking of this:
> http://sourceware.org/ml/gdb-patches/2004-12/msg00249.html
> http://sourceware.org/ml/gdb-patches/2005-06/msg00242.html
>
> I think someone needs to combine Joel's and Jan's patches. Joel's is
> nicer in that it uses branch_dest and the right mask for blrl; Jan's
> is nicer in that it checks whether lr was saved or is now lost.

Attached for:
http://sourceware.org/ml/gdb-patches/2004-12/msg00249.html
and it does not handle in any way
http://sourceware.org/ml/gdb-patches/2005-06/msg00242.html
as it would be IMO more appropriate to base it on the called code content but
"I do not have that Darwin code".

Regards,
Jan

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2007-01-14 Joel Brobecker <brobecker@gnat.com>
Jan Kratochvil <jan.kratochvil@redhat.com>

* rs6000-tdep.c (bl_to_blrl_insn_p): New function.
(skip_prologue): Allow bl->blrl used by a PIC code.

--- gdb/rs6000-tdep.c 9 Jan 2007 17:58:57 -0000 1.260
+++ gdb/rs6000-tdep.c 14 Jan 2007 21:24:51 -0000
@@ -902,6 +902,30 @@ 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)
{
@@ -1133,18 +1157,19 @@ 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))
+ {
+ /* If we did not yet retrieved LR into some GPR
+ all our chances are lost. On the other hand already
+ stored LR is still kept intact in its GPR. */
+ if (lr_reg == -1)
+ {
+ /* Invalidate lr_reg, but don't set it to -1.
+ That would mean that it had never been set. */
+ lr_reg = -2;
+ }
+ continue;
}

op = read_memory_integer (pc + 4, 4);