Fix skipping stack protector on arm

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.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 9901d164ba7fda52cacddb60bf373223823939b8..708b78b16843f8be9cf33a1993aac533a5d1be5f 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -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

diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c
index ef75fe2bc9dcecdfebedb93b056907e06e227b59..699254bd3b2ffb75efee703cbddcd4eb00db3ad6 100644 (file)
--- a/gdb/arm-tdep.c
+++ b/gdb/arm-tdep.c
@@ -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;
        }