[PATCH 2/4] Match instruction adjusts SP in thumb

Yao Qi
2014-07-03T06:11:47Z

This is a refactor patch, that moves matching instructions adjusting
SP into a new function, thumb_instruction_restores_sp. The second
call to thumb_instruction_restores_sp in thumb_in_function_epilogue_p
is a little different from the original. The original code matches
'POP <registers> without PC', but thumb_in_function_epilogue_p matches
'POP <registers> (with and without PC)'. However, GDB found one
instruction about return and is scanning the previous instruction,
which should be an instruction about return too, so the code change
doesn't affect the functionality.

gdb:

2014-07-02 Yao Qi <yao@codesourcery.com>

* arm-tdep.c (thumb_instruction_restores_sp): New function.
(thumb_in_function_epilogue_p): Call
thumb_instruction_restores_sp.
---
gdb/arm-tdep.c | 25 ++++++++++++++-----------
1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c
index 0fc7fc1..153ef42 100644
--- a/gdb/arm-tdep.c
+++ b/gdb/arm-tdep.c
@@ -685,6 +685,17 @@ thumb2_instruction_changes_pc (unsigned short inst1, unsigned short inst2)
return 0;
}

+/* Return 1 if the 16-bit Thumb instruction INSN restores SP in
+ epilogue, 0 otherwise. */
+
+static int
+thumb_instruction_restores_sp (unsigned short insn)
+{
+ return (insn == 0x46bd /* mov sp, r7 */
+ || (insn & 0xff80) == 0xb000 /* add sp, imm */
+ || (insn & 0xfe00) == 0xbc00); /* pop <registers> */
+}
+
/* Analyze a Thumb prologue, looking for a recognizable stack frame
and frame pointer. Scan until we encounter a store that could
clobber the stack frame unexpectedly, or an unknown instruction.
@@ -3257,14 +3268,10 @@ thumb_in_function_epilogue_p (struct gdbarch *gdbarch, CORE_ADDR pc)
found_return = 1;
else if (insn == 0x46f7) /* mov pc, lr */
found_return = 1;
- else if (insn == 0x46bd) /* mov sp, r7 */
- found_stack_adjust = 1;
- else if ((insn & 0xff80) == 0xb000) /* add sp, imm */
- found_stack_adjust = 1;
- else if ((insn & 0xfe00) == 0xbc00) /* pop <registers> */
+ else if (thumb_instruction_restores_sp (insn))
{
found_stack_adjust = 1;
- if (insn & 0x0100) /* <registers> include PC. */
+ if ((insn & 0xfe00) == 0xbd00) /* pop <registers, PC> */
found_return = 1;
}
else if (thumb_insn_size (insn) == 4) /* 32-bit Thumb-2 instruction */
@@ -3317,11 +3324,7 @@ thumb_in_function_epilogue_p (struct gdbarch *gdbarch, CORE_ADDR pc)
insn = extract_unsigned_integer (buf, 2, byte_order_for_code);
insn2 = extract_unsigned_integer (buf + 2, 2, byte_order_for_code);

- if (insn2 == 0x46bd) /* mov sp, r7 */
- found_stack_adjust = 1;
- else if ((insn2 & 0xff80) == 0xb000) /* add sp, imm */
- found_stack_adjust = 1;
- else if ((insn2 & 0xff00) == 0xbc00) /* pop <registers> without PC */
+ if (thumb_instruction_restores_sp (insn2))
found_stack_adjust = 1;
else if (insn == 0xe8bd) /* ldm.w sp!, <registers> */
found_stack_adjust = 1;
--
1.9.0