From 808f7ab1fc88da40007c17a20e49928359f27491 Mon Sep 17 00:00:00 2001 From: Yao Qi Date: Wed, 2 Jul 2014 15:16:26 +0800 Subject: [PATCH] Stop prologue analysis when past the epilogue We see a fail in gdb.trace/entry-values.exp on armv4t thumb, bt^M #0 0x000086fc in foo (i=0, i@entry=, j=2, j@entry=)^M #1 0x00000002 in ?? ()^M Backtrace stopped: previous frame identical to this frame (corrupt stack?)^M (gdb) FAIL: gdb.trace/entry-values.exp: bt (1) (pattern 1) The fail is caused by incorrect prologue analysis, which can be illustrated by setting a breakpoint on function foo, (gdb) disassemble foo Dump of assembler code for function foo: 0x000086e8 <+0>: push {r7, lr} 0x000086ea <+2>: sub sp, #8 0x000086ec <+4>: add r7, sp, #0 0x000086ee <+6>: str r0, [r7, #4] 0x000086f0 <+8>: str r1, [r7, #0] 0x000086f2 <+10>: movs r3, #0 0x000086f4 <+12>: adds r0, r3, #0 0x000086f6 <+14>: mov sp, r7 0x000086f8 <+16>: add sp, #8 0x000086fa <+18>: pop {r7} 0x000086fc <+20>: pop {r1} 0x000086fe <+22>: bx r1 End of assembler dump. (gdb) b foo Breakpoint 1 at 0x86fc As we can see, GDB analyzes the prologue and skip the prologue to the last instruction but one. The breakpoint is set within the epilogue, and GDB skips too many instruction for prologue. This patch teaches GDB to stop prologue analysis when goes into the epilogue. With this patch applied, GDB is able to unwind correctly, (gdb) bt #0 0x000086f6 in foo (i=0, i@entry=2, j=2, j@entry=3) #1 0x00008718 in bar (i=) #2 0x00008758 in main () gdb: 2014-07-11 Yao Qi * arm-tdep.c (thumb_analyze_prologue): Break the loop if thumb_instruction_restores_sp return true. --- gdb/ChangeLog | 5 +++++ gdb/arm-tdep.c | 5 +++++ 2 files changed, 10 insertions(+) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index 7bc1d03d9e4..1ccacd34da2 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,8 @@ +2014-07-11 Yao Qi + + * arm-tdep.c (thumb_analyze_prologue): Break the loop if + thumb_instruction_restores_sp return true. + 2014-07-11 Yao Qi * arm-tdep.c (thumb_instruction_restores_sp): New function. diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c index 0e7d9c2f872..cb0030c4b10 100644 --- a/gdb/arm-tdep.c +++ b/gdb/arm-tdep.c @@ -754,6 +754,11 @@ thumb_analyze_prologue (struct gdbarch *gdbarch, regs[ARM_SP_REGNUM] = pv_add_constant (regs[ARM_SP_REGNUM], -offset); } + else if (thumb_instruction_restores_sp (insn)) + { + /* Don't scan past the epilogue. */ + break; + } else if ((insn & 0xf800) == 0xa800) /* add Rd, sp, #imm */ regs[bits (insn, 8, 10)] = pv_add_constant (regs[ARM_SP_REGNUM], (insn & 0xff) << 2); -- 2.30.2