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runtime: use saved LR when unwinding through morestack

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On LR machine, consider F calling G calling H, which grows stack.
The stack looks like
...
G's frame:
	... locals ...
	saved LR = return PC in F  <- SP points here at morestack
H's frame (to be created)

At morestack, we save
	gp.sched.pc = H's morestack call
	gp.sched.sp = H's entry SP (the arrow above)
	gp.sched.lr = return PC in G

Currently, when unwinding through morestack (if _TraceJumpStack
is set), we switch PC and SP but not LR. We then have
	frame.pc = H's morestack call
	frame.sp = H's entry SP (the arrow above)
As LR is not set, we load it from stack at *sp, so
	frame.lr = return PC in F
As the SP hasn't decremented at the morestack call,
	frame.fp = frame.sp = H's entry SP

Unwinding a frame, we have
	frame.pc = old frame.lr = return PC in F
	frame.sp = old frame.fp = H's entry SP a.k.a. G's SP
The PC and SP don't match. The unwinding will go off if F and G
have different frame sizes.

Fix this by preserving the LR when switching stack.

Also add code to detect infinite loop in unwinding.

TODO: add some test. I can reproduce the infinite loop (or throw
with added check) but the frequency is low.

May fix #52116.

Change-Id: I6e1294f1c6e55f664c962767a1cf6c466a0c0eff
Reviewed-on: https://go-review.googlesource.com/c/go/+/400575
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Cherry Mui <cherryyz@google.com>
Reviewed-by: Eric Fang <eric.fang@arm.com>
Reviewed-by: Benny Siegert <bsiegert@gmail.com>
This commit is contained in:
Cherry Mui 2022-04-15 12:23:06 -04:00
parent 0eb93d6b43
commit 74f0009422
1 changed files with 13 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
src/runtime/traceback.go
View File

@ -82,6 +82,7 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in
}
waspanic := false
cgoCtxt := gp.cgoCtxt
stack := gp.stack
printing := pcbuf == nil && callback == nil
// If the PC is zero, it's likely a nil function call.
@ -114,7 +115,7 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in
if !f.valid() {
if callback != nil || printing {
print("runtime: g ", gp.goid, ": unknown pc ", hex(frame.pc), "\n")
tracebackHexdump(gp.stack, &frame, 0)
tracebackHexdump(stack, &frame, 0)
}
if callback != nil {
throw("unknown pc")
@ -174,12 +175,15 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in
frame.fn = findfunc(frame.pc)
f = frame.fn
flag = f.flag
frame.lr = gp.m.curg.sched.lr
frame.sp = gp.m.curg.sched.sp
stack = gp.m.curg.stack
cgoCtxt = gp.m.curg.cgoCtxt
case funcID_systemstack:
// systemstack returns normally, so just follow the
// stack transition.
frame.sp = gp.m.curg.sched.sp
stack = gp.m.curg.stack
cgoCtxt = gp.m.curg.cgoCtxt
flag &^= funcFlag_SPWRITE
}
@ -248,7 +252,7 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in
}
if callback != nil || doPrint {
print("runtime: g ", gp.goid, ": unexpected return pc for ", funcname(f), " called from ", hex(frame.lr), "\n")
tracebackHexdump(gp.stack, &frame, lrPtr)
tracebackHexdump(stack, &frame, lrPtr)
}
if callback != nil {
throw("unknown caller pc")
@ -477,6 +481,13 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in
break
}
if frame.pc == frame.lr && frame.sp == frame.fp {
// If the next frame is identical to the current frame, we cannot make progress.
print("runtime: traceback stuck. pc=", hex(frame.pc), " sp=", hex(frame.sp), "\n")
tracebackHexdump(stack, &frame, frame.sp)
throw("traceback stuck")
}
// Unwind to next frame.
frame.fn = flr
frame.pc = frame.lr