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Support for leaf functions which don't touch any callee-saved registers

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for Windows x64 stacks.

According to https://reviews.llvm.org/D2474, LLVM does't generate unwind info for leaf function which doesn't touch any callee-saved
registers. According to MSDN, leaf functions can be unwound simply by
simulating a return.

Change-Id: Ic0503e2aca90b0ba5799133ea8439f1b5f2eefda
Reviewed-on: https://chromium-review.googlesource.com/c/breakpad/breakpad/+/3489332
Reviewed-by: Mark Mentovai <mark@chromium.org>
Reviewed-by: Joshua Peraza <jperaza@chromium.org>
This commit is contained in:
Ivan Penkov
2022-02-24 20:49:43 +00:00
parent 88f5fc451e
commit 622a582fa6
3 changed files with 53 additions and 4 deletions
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41
src/processor/stackwalker_amd64.cc
View File

@@ -221,6 +221,35 @@ StackFrameAMD64* StackwalkerAMD64::GetCallerByFramePointerRecovery(
return NULL;
}
StackFrameAMD64* StackwalkerAMD64::GetCallerBySimulatingReturn(
const vector<StackFrame*>& frames) {
assert(frames.size() == 1);
StackFrameAMD64* last_frame = static_cast<StackFrameAMD64*>(frames.back());
uint64_t last_rsp = last_frame->context.rsp;
uint64_t caller_rip_address, caller_rip;
int searchwords = 1;
if (!ScanForReturnAddress(last_rsp, &caller_rip_address, &caller_rip,
searchwords)) {
// No plausible return address at the top of the stack. Unable to simulate
// a return.
return NULL;
}
// Create a new stack frame (ownership will be transferred to the caller)
// and fill it in.
StackFrameAMD64* frame = new StackFrameAMD64();
frame->trust = StackFrame::FRAME_TRUST_LEAF;
frame->context = last_frame->context;
frame->context.rip = caller_rip;
// The caller's %rsp is directly underneath the return address pushed by
// the call.
frame->context.rsp = caller_rip_address + 8;
frame->context_validity = last_frame->context_validity;
return frame;
}
StackFrameAMD64* StackwalkerAMD64::GetCallerByStackScan(
const vector<StackFrame*>& frames) {
StackFrameAMD64* last_frame = static_cast<StackFrameAMD64*>(frames.back());
@@ -282,12 +311,22 @@ StackFrame* StackwalkerAMD64::GetCallerFrame(const CallStack* stack,
StackFrameAMD64* last_frame = static_cast<StackFrameAMD64*>(frames.back());
scoped_ptr<StackFrameAMD64> new_frame;
// If we have DWARF CFI information, use it.
// If we have CFI information, use it.
scoped_ptr<CFIFrameInfo> cfi_frame_info(
frame_symbolizer_->FindCFIFrameInfo(last_frame));
if (cfi_frame_info.get())
new_frame.reset(GetCallerByCFIFrameInfo(frames, cfi_frame_info.get()));
// If CFI was not available and this is a Windows x64 stack, check whether
// this is a leaf function which doesn't touch any callee-saved registers.
// According to https://reviews.llvm.org/D24748, LLVM doesn't generate unwind
// info for such functions. According to MSDN, leaf functions can be unwound
// simply by simulating a return.
if (!new_frame.get() && stack->frames()->size() == 1 &&
system_info_->os_short == "windows") {
new_frame.reset(GetCallerBySimulatingReturn(frames));
}
// If CFI was not available or failed, try using frame pointer recovery.
// Never try to use frame pointer unwinding on Windows x64 stack. MSVC never
// generates code that works with frame pointer chasing, and LLVM does the

5
src/processor/stackwalker_amd64.h
View File

@@ -90,6 +90,11 @@ class StackwalkerAMD64 : public Stackwalker {
// of the returned frame. Return NULL on failure.
StackFrameAMD64* GetCallerByStackScan(const vector<StackFrame*>& frames);
// Trying to simulate a return. The caller takes ownership of the returned
// frame. Return NULL on failure.
StackFrameAMD64* GetCallerBySimulatingReturn(
const vector<StackFrame*>& frames);
// Stores the CPU context corresponding to the innermost stack frame to
// be returned by GetContextFrame.
const MDRawContextAMD64* context_;