[lldb-dev] Problem unwinding from inside of a CRT function

[Zachary Turner]

BTW, probably a given, but I'm doing this on Windows with a Windows
executable.  So it could be something to do with that as well, but I'm not
really familiar with how the unwinder works.

FWIW it never calls RegisterContext::CreateRegisterContextForFrameIndex
with any index other than 0.

On Thu Jan 15 2015 at 3:56:52 PM Zachary Turner <zturner at google.com> wrote:

> Having some trouble unwinding when I'm broken inside of a CRT function.
> Another caveat is that I don't have symbols for this CRT function.  So the
> problem could be anything from something I've done wrong on my side, to an
> issue when symbols aren't present, to something else.  Here is the source
> code of this program:
>
> #include <stdio.h>
>
> int main (void)
> {
>   printf("This is line 1\n");
>   printf("This is line 2\n");
>   printf("This is line 3\n");
>   return 1;
> }
>
> Here is the disassembly of main:
>
> (lldb) disassemble -n main -F intel
>    0x1235040 <main>: push   ebp
>    0x1235041 <main+1>: mov    ebp, esp
>    0x1235043 <main+3>: sub    esp, 0x14
>    0x1235046 <main+6>: lea    eax, [0x1230040]
>    0x123504c <main+12>: mov    dword ptr [ebp - 0x4], 0x0
>    0x1235053 <main+19>: mov    dword ptr [esp], eax
>    0x1235056 <main+22>: call   0x12350a1
>    0x123505b <main+27>: lea    ecx, [0x1230050]
>    (snipped for brevity)
>
> (Using the argument to "call" as the breakpoint address)
> (lldb) break set -a 0x12350a1
> Breakpoint 3: address = 0x012350a1
> (lldb) run
> Process 17044 launching
> (lldb) Process 17044 launched: 'd:\testexe\expr_test.exe' (i386)
> (lldb) Process 17044 stopped
> * thread #1: tid = 0x40ec, 0x012350a1 expr_test.exe, stop reason =
> breakpoint 3.1
>     frame #0: 0x012350a1 expr_test.exe
> -> 0x12350a1: pushl  $0xc
>    0x12350a3: pushl  $0x1241000
>    0x12350a8: calll  0x1235be0
>    0x12350ad: xorl   %edi, %edi
> (lldb) disassemble -b -F intel
> -> 0x12350a1: 6a 0c           push   0xc
>    0x12350a3: 68 00 10 24 01  push   0x1241000
>    0x12350a8: e8 33 0b 00 00  call   0x1235be0
>    0x12350ad: 33 ff           xor    edi, edi
>    0x12350af: 89 7d e4        mov    dword ptr [ebp - 0x1c], edi
>    0x12350b2: 33 c0           xor    eax, eax
>    0x12350b4: 39 45 08        cmp    dword ptr [ebp + 0x8], eax
>    0x12350b7: 0f 95 c0        setne  al
>    0x12350ba: 85 c0           test   eax, eax
>    0x12350bc: 75 15           jne    0x12350d3
>
> Here's my register values:
> (lldb) register read
> General Purpose Registers:
>        eax = 0x01230040
>        ebx = 0x00000000
>        ecx = 0x00000001
>        edx = 0x00000000
>        edi = 0x00000000
>        esi = 0x00000000
>        ebp = 0x00EAF920
>        esp = 0x00EAF908
>        eip = 0x012350A1
>     eflags = 0b00000000000000000000001000010110
>
> And using the value of esp to dump the stack (sorry, I don't know how to
> use the -f argument to format this more nicely),
>
> (lldb) memory read 0x00EAF908
> 0x00eaf908: 5b 50 23 01 40 00 23 01 00 00 00 00 00 00 00 00
>  [P#. at .#.........
> 0x00eaf918: 28 f9 ea 00 00 00 00 00 68 f9 ea 00 4e 52 23 01
>  (.......h...NR#.
>
> So the return address is 0x0123505b.  Cross-referencing this with the
> original disassembly of main(), it looks like this is the correct value.
>
> So it seems like the Unwinder has all the information it needs, but yet
> I'm still only getting 1 frame.  Any suggestions how to dig into this?
>
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