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Fix skipping stack protector on arm

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This patch fixes the bug in my patch skipping stack protector
https://www.sourceware.org/ml/gdb-patches/2010-12/msg00110.html

In my skipping stack protector patch, I misunderstood the constant vs.
immediate on instruction encodings, and treated immediate as constant
by mistake.  The instruction 'ldr Rd, [PC, #immed]' loads the
address of __stack_chk_guard to Rd, and #immed is an offset from PC.
We should get the __stack_chk_guard from *(pc + #immed).

As a result of this mistake, arm_analyze_load_stack_chk_guard returns
the wrong address of __stack_chk_guard, and the symbol
__stack_chk_guard can't be found.  However, we continue to match the
following instructions when symbol isn't found, so the code still
works.  In other words, the code just matches the instruction pattern
without checking __stack_chk_guard symbol correctly.

Joel's patch <https://sourceware.org/ml/gdb-patches/2014-10/msg00605.html>
makes the heuristics stricter that we stop matching instructions if
symbol __stack_chk_guard isn't found.  Then the bug is exposed.  This
patch is to correct the load address computation for ldr instruction,
and it fixes some fails in gdb.mi/gdb792.exp on armv4t both arm and
thumb mode.

Regression tested on arm-linux-gnueabi target with
{armv4t, armv7-a} x {marm, mthumb} x {-fstack-protector,-fno-stack-protector}

gdb:

2014-10-29  Yao Qi  <yao@codesourcery.com>

	* arm-tdep.c (arm_analyze_load_stack_chk_guard): Compute the
	loaded address correctly of ldr instruction.
This commit is contained in:
Yao Qi 2014-10-29 13:39:16 +08:00
parent 5e1b37e7a3
commit 6ae274b7dc
2 changed files with 13 additions and 3 deletions
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5
gdb/ChangeLog
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@ -1,3 +1,8 @@
2014-10-29 Yao Qi <yao@codesourcery.com>
* arm-tdep.c (arm_analyze_load_stack_chk_guard): Compute the
loaded address correctly of ldr instruction.
2014-10-28 Pedro Alves <palves@redhat.com>
PR gdb/12623

11
gdb/arm-tdep.c
View File

@ -1204,7 +1204,9 @@ arm_analyze_load_stack_chk_guard(CORE_ADDR pc, struct gdbarch *gdbarch,
{
*destreg = bits (insn1, 8, 10);
*offset = 2;
address = bits (insn1, 0, 7);
address = (pc & 0xfffffffc) + 4 + (bits (insn1, 0, 7) << 2);
address = read_memory_unsigned_integer (address, 4,
byte_order_for_code);
}
else if ((insn1 & 0xfbf0) == 0xf240) /* movw Rd, #const */
{
@ -1233,9 +1235,12 @@ arm_analyze_load_stack_chk_guard(CORE_ADDR pc, struct gdbarch *gdbarch,
unsigned int insn
= read_memory_unsigned_integer (pc, 4, byte_order_for_code);
if ((insn & 0x0e5f0000) == 0x041f0000) /* ldr Rd, #immed */
if ((insn & 0x0e5f0000) == 0x041f0000) /* ldr Rd, [PC, #immed] */
{
address = bits (insn, 0, 11);
address = bits (insn, 0, 11) + pc + 8;
address = read_memory_unsigned_integer (address, 4,
byte_order_for_code);
*destreg = bits (insn, 12, 15);
*offset = 4;
}