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runtime: start ARM atomic kernel helper traceback in caller

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Like the VDSO, we cannot directly traceback from the Linux kernel ARM
atomic/barrier helpers. However, unlike the VDSO, this functions are
extremely simple. Neither of the functions we use, kuser_cmpxchg and
kuser_memory_barrier, touch SP or LR.

We can use this to our advantage to read LR and simply start tracebacks
in the caller.

Fixes #49182

Change-Id: I890edbeb7c128938000fe7baf6f913c02a956edd
Reviewed-on: https://go-review.googlesource.com/c/go/+/362977
Trust: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
This commit is contained in:
Michael Pratt 2021-11-10 12:56:40 -05:00
parent 76fbd61673
commit 3634594790
1 changed files with 14 additions and 0 deletions
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14
src/runtime/traceback.go
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@ -96,6 +96,20 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in
} }
} }
// runtime/internal/atomic functions call into kernel helpers on
// arm < 7. See runtime/internal/atomic/sys_linux_arm.s.
//
// Start in the caller's frame.
if GOARCH == "arm" && goarm < 7 && GOOS == "linux" && frame.pc&0xffff0000 == 0xffff0000 {
// Note that the calls are simple BL without pushing the return
// address, so we use LR directly.
//
// The kernel helpers are frameless leaf functions, so SP and
// LR are not touched.
frame.pc = frame.lr
frame.lr = 0
}
f := findfunc(frame.pc) f := findfunc(frame.pc)
if !f.valid() { if !f.valid() {
if callback != nil || printing { if callback != nil || printing {