Commit 597f87c9 authored by Russ Cox's avatar Russ Cox

runtime: do not trace past jmpdefer during pprof traceback on arm

jmpdefer modifies PC, SP, and LR, and not atomically,
so walking past jmpdefer will often end up in a state
where the three are not a consistent execution snapshot.
This was causing warning messages a few frames later
when the traceback realized it was confused, but given
the right memory it could easily crash instead.

Update #8153

LGTM=minux, iant
R=golang-codereviews, minux, iant
CC=golang-codereviews, r
https://golang.org/cl/107970043
parent 36207a91
......@@ -394,6 +394,10 @@ TEXT runtime·lessstack(SB), NOSPLIT, $-4-0
// 1. grab stored LR for caller
// 2. sub 4 bytes to get back to BL deferreturn
// 3. B to fn
// TODO(rsc): Push things on stack and then use pop
// to load all registers simultaneously, so that a profiling
// interrupt can never see mismatched SP/LR/PC.
// (And double-check that pop is atomic in that way.)
TEXT runtime·jmpdefer(SB), NOSPLIT, $0-8
MOVW 0(SP), LR
MOVW $-4(LR), LR // BL deferreturn
......
......@@ -110,6 +110,19 @@ runtime·gentraceback(uintptr pc0, uintptr sp0, uintptr lr0, G *gp, int32 skip,
if(runtime·topofstack(f)) {
frame.lr = 0;
flr = nil;
} else if(f->entry == (uintptr)runtime·jmpdefer) {
// jmpdefer modifies SP/LR/PC non-atomically.
// If a profiling interrupt arrives during jmpdefer,
// the stack unwind may see a mismatched register set
// and get confused. Stop if we see PC within jmpdefer
// to avoid that confusion.
// See golang.org/issue/8153.
// This check can be deleted if jmpdefer is changed
// to restore all three atomically using pop.
if(callback != nil)
runtime·throw("traceback_arm: found jmpdefer when tracing with callback");
frame.lr = 0;
flr = nil;
} else {
if((n == 0 && frame.sp < frame.fp) || frame.lr == 0)
frame.lr = *(uintptr*)frame.sp;
......
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