[PATCH] add 'rs6000_in_function_epilogue_p()'

Paul Gilliam
2005-11-30T19:55:14Z

This patch fixes a problem when watching local variables on PowerPC.

Here is a reference from the gdb mailing list:
http://sourceware.org/ml/gdb/2005-11/msg00602.html

I know the patch uses a depreciated function and I am open to ideas.
Here is a reference from the gdb mailing list about ideas to avoid using the depreciated function:
http://sourceware.org/ml/gdb/2005-11/msg00623.html

I wanted to submit this patch as a starting point, but if it is acceptable, I'll commit it.

2005-11-30 Paul Gilliam <pgilliam@us.ibm.com>

* rs6000-tdep.c: Add new subroutine, 'rs6000_in_function_epilogue_p()'
and put it into the architecture vector.

Index: rs6000-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/rs6000-tdep.c,v
retrieving revision 1.248
diff -a -u -p -r1.248 rs6000-tdep.c
--- rs6000-tdep.c 1 Nov 2005 19:32:36 -0000 1.248
+++ rs6000-tdep.c 30 Nov 2005 18:59:27 -0000
@@ -502,6 +502,63 @@ rs6000_skip_prologue (CORE_ADDR pc)
return pc;
}

+static int
+insn_changes_sp(unsigned long insn)
+{
+ int opcode = (insn>>26) & 0x03f;
+ int sd = (insn>>21) & 0x01f;
+ int a = (insn>>16) & 0x01f;
+ int b = (insn>>11) & 0x01f;
+ int subcode = (insn>> 1) & 0x3ff;
+ int rc = insn & 0x001;
+
+ if (opcode == 31 && subcode == 444 && a == 1)
+ return 1; /* mr R1,Rn */
+ if (opcode == 14 && sd == 1)
+ return 1; /* addi R1,Rn,simm */
+ if (opcode == 58 && sd == 1)
+ return 1; /* ld R1,ds(Rn) */
+
+ return 0;
+}
+
+/* Return true if we are in the functin's epilogue, i.e. after the
+ instruction that destroyed the function's stack frame. */
+static int
+rs6000_in_function_epilogue_p (struct gdbarch *gdbarch, CORE_ADDR pc)
+{
+ bfd_byte insn_buf[PPC_INSN_SIZE];
+ CORE_ADDR scan_pc, func_addr, func_end;
+ unsigned long insn;
+
+ /* Find the search limits. */
+ if (!find_pc_partial_function (pc, NULL, &func_addr, &func_end))
+ return 0;
+
+ /* Scan forward untill next 'blr'. */
+ for (scan_pc = pc; scan_pc < func_end; scan_pc += PPC_INSN_SIZE)
+ {
+ if (deprecated_read_memory_nobpt (scan_pc, insn_buf, PPC_INSN_SIZE))
+ return 0;
+ insn = extract_signed_integer (insn_buf, PPC_INSN_SIZE);
+ if (insn == 0x4e800020) break;
+ if (insn_changes_sp(insn))
+ return 0;
+ }
+
+ /* Scan backward untill adjustment to stack pointer (R1). */
+ for (scan_pc=pc-PPC_INSN_SIZE; scan_pc>=func_addr; scan_pc-=PPC_INSN_SIZE)
+ {
+ if (deprecated_read_memory_nobpt (scan_pc, insn_buf, PPC_INSN_SIZE))
+ return 0;
+ insn = extract_signed_integer (insn_buf, PPC_INSN_SIZE);
+ if (insn_changes_sp(insn))
+ return 1;
+ }
+
+ return 0;
+}
+

/* Fill in fi->saved_regs */

@@ -3342,6 +3399,8 @@ rs6000_gdbarch_init (struct gdbarch_info
set_gdbarch_deprecated_extract_struct_value_address (gdbarch, rs6000_extract_struct_value_address);

set_gdbarch_skip_prologue (gdbarch, rs6000_skip_prologue);
+ set_gdbarch_in_function_epilogue_p (gdbarch, rs6000_in_function_epilogue_p);
+
set_gdbarch_inner_than (gdbarch, core_addr_lessthan);
set_gdbarch_breakpoint_from_pc (gdbarch, rs6000_breakpoint_from_pc);