From 02e5a8fdfcc8e237f5b55618ccbe9ad845014427 Mon Sep 17 00:00:00 2001 From: Russ Cox Date: Fri, 19 Feb 2021 06:01:25 -0500 Subject: [PATCH] runtime: ignore SPWRITE in syscall functions netbsd/amd64's Syscall9 changes SP using ADD and SUB, which are treated as SPWRITEs (they are not accounted for in the sp-adjust tracking, and there are too many functions that would report mismatched stack adjustments at RET if they were). A traceback starting in Syscall9 as saved by entersyscall complains about the SPWRITE-ness unnecessarily, since the PC/SP are saved at the start of the function. Ignore SPWRITE in that case. netbsd/arm's Syscall6 also changes SP (R13), using a direct write. So even if we could handle the ADD/SUB in the amd64 case or rewrote that assembly, we'd still be stuck with a more difficult problem in this case. Ignoring the SPWRITE fixes it. Example crashes: https://build.golang.org/log/160fc7b051a2cf90782b75a99984fff129329e66 https://build.golang.org/log/7879e2fecdb400eee616294285e1f952e5b17301 Change-Id: I0c8e9696066e90dafed6d4a93d11697da23f0080 Reviewed-on: https://go-review.googlesource.com/c/go/+/294072 Reviewed-by: Cherry Zhang Trust: Russ Cox Run-TryBot: Russ Cox --- src/runtime/traceback.go | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/src/runtime/traceback.go b/src/runtime/traceback.go index eb185eecd36..53eb6898482 100644 --- a/src/runtime/traceback.go +++ b/src/runtime/traceback.go @@ -174,6 +174,12 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in // So we don't need to exclude it with the other SP-writing functions. flag &^= funcFlag_SPWRITE } + if frame.pc == pc0 && frame.sp == sp0 && pc0 == gp.syscallpc && sp0 == gp.syscallsp { + // Some Syscall functions write to SP, but they do so only after + // saving the entry PC/SP using entersyscall. + // Since we are using the entry PC/SP, the later SP write doesn't matter. + flag &^= funcFlag_SPWRITE + } // Found an actual function. // Derive frame pointer and link register.