https://llvm.org/bugs/show_bug.cgi?id=27687
Bug ID: 27687
Summary: We cannot backtrace out of fflush() on Linux x86_64
Product: lldb
Version: unspecified
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: All Bugs
Assignee: lldb-dev@lists.llvm.org
Reporter: lab...@google.com
CC: llvm-b...@lists.llvm.org
Classification: Unclassified
This is happening in TestPrintStackTraces, where we can end up here:
ld-linux-x86-64.so.2`___lldb_unnamed_symbol95$$ld-linux-x86-64.so.2:
0x7ffff7df04e0 <+0>: 48 83 ec 38 subq
$0x38, %rsp
0x7ffff7df04e4 <+4>: 48 89 04 24 movq
%rax, (%rsp)
0x7ffff7df04e8 <+8>: 48 89 4c 24 08 movq
%rcx, 0x8(%rsp)
0x7ffff7df04ed <+13>: 48 89 54 24 10 movq
%rdx, 0x10(%rsp)
0x7ffff7df04f2 <+18>: 48 89 74 24 18 movq
%rsi, 0x18(%rsp)
0x7ffff7df04f7 <+23>: 48 89 7c 24 20 movq
%rdi, 0x20(%rsp)
0x7ffff7df04fc <+28>: 4c 89 44 24 28 movq
%r8, 0x28(%rsp)
0x7ffff7df0501 <+33>: 4c 89 4c 24 30 movq
%r9, 0x30(%rsp)
0x7ffff7df0506 <+38>: 48 8b 74 24 40 movq
0x40(%rsp), %rsi
0x7ffff7df050b <+43>: 48 8b 7c 24 38 movq
0x38(%rsp), %rdi
0x7ffff7df0510 <+48>: e8 4b 8f ff ff callq
0x7ffff7de9460 ; ___lldb_unnamed_symbol54$$ld-linux-x86-64.so.2
0x7ffff7df0515 <+53>: 49 89 c3 movq
%rax, %r11
0x7ffff7df0518 <+56>: 4c 8b 4c 24 30 movq
0x30(%rsp), %r9
0x7ffff7df051d <+61>: 4c 8b 44 24 28 movq
0x28(%rsp), %r8
0x7ffff7df0522 <+66>: 48 8b 7c 24 20 movq
0x20(%rsp), %rdi
0x7ffff7df0527 <+71>: 48 8b 74 24 18 movq
0x18(%rsp), %rsi
0x7ffff7df052c <+76>: 48 8b 54 24 10 movq
0x10(%rsp), %rdx
0x7ffff7df0531 <+81>: 48 8b 4c 24 08 movq
0x8(%rsp), %rcx
-> 0x7ffff7df0536 <+86>: 48 8b 04 24 movq
(%rsp), %rax
0x7ffff7df053a <+90>: 48 83 c4 48 addq
$0x48, %rsp
0x7ffff7df053e <+94>: 41 ff e3 jmpq
*%r11
0x7ffff7df0541 <+97>: 66 66 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 nopw
%cs:(%rax,%rax)
image show-unwind --address 0x7ffff7df0536
UNWIND PLANS for
ld-linux-x86-64.so.2`___lldb_unnamed_symbol95$$ld-linux-x86-64.so.2 (start addr
0x7ffff7df04e0)
Asynchronous (not restricted to call-sites) UnwindPlan is 'assembly insn
profiling'
Synchronous (restricted to call-sites) UnwindPlan is 'eh_frame CFI'
Assembly language inspection UnwindPlan:
This UnwindPlan originally sourced from assembly insn profiling
This UnwindPlan is sourced from the compiler: no.
This UnwindPlan is valid at all instruction locations: yes.
Address range of this UnwindPlan: [ld-linux-x86-64.so.2..text +
88576-0x0000000000015a70)
row[0]: 0: CFA=rsp +8 => rsp=CFA+0 rip=[CFA-8]
row[1]: 4: CFA=rsp+64 => rsp=CFA+0 rip=[CFA-8]
row[2]: 94: CFA=rsp -8 => rsp=CFA+0 rip=[CFA-8]
eh_frame UnwindPlan:
This UnwindPlan originally sourced from eh_frame CFI
This UnwindPlan is sourced from the compiler: yes.
This UnwindPlan is valid at all instruction locations: no.
Address range of this UnwindPlan: [ld-linux-x86-64.so.2..text +
88576-0x0000000000015a61)
row[0]: 0: CFA=rsp+24 => rip=[CFA-8]
row[1]: 4: CFA=rsp+80 => rip=[CFA-8]
row[2]: 94: CFA=rsp +8 => rip=[CFA-8]
So the, eh_frame unwind plan is actually correct, but we are using the assembly
emulation unwind plan, which ends up being hopelessly incorrect, as the
function we are in does not have a normal stack frame (it exits via a tail
call, and I think it is entered by one as well). The unwind machinery
eventually picks itself up, but not before skipping a couple of frames on the
stack.
We should find a way to get lldb to use eh_frame plan (or
eh_frame+augmentation) here.
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