runtime: c-shared with LD_PRELOAD does not work for some programs #12465
Comments
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A backtrace extracted from a core of The bug occurs when |
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Thanks for the backtrace. This is the Go signal handler receiving a SIGCHLD signal. It's not a problem for getg to return nil in sigtrampgo. That just means that a signal occurred on a non-Go thread. The Go code is going to do some shuffling and eventually raise the signal on a C thread, with the C signal handler installed. That should cause the right thing to happen. However, in this backtrace, the shuffling fails because the sigaltstack system call fails. I think that sigaltstack must be returning EPERM: an attempt was made to change the alternate signal stack while the process was already executing on the alternate signal stack. That could happen if the C program create a thread, called sigaltstack on that thread, and then received a signal. That might explain why you are not seeing a problem with relatively simple programs, but only with relatively complex ones. If that is indeed the problem, the solution may be relatively simple: if sigaltstack fails due to EPERM, we should fetch the current alternative signal stack and use it to set the value of m.gsignal.stack. |
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Hi, @ianlancetaylor Thank you very much for your comment. After applying this fix (for commit dab0da), diff --git a/src/runtime/os1_linux.go b/src/runtime/os1_linux.go
index c23dc30..99a2560 100644
--- a/src/runtime/os1_linux.go
+++ b/src/runtime/os1_linux.go
@@ -326,7 +326,15 @@ func getsig(i int32) uintptr {
}
func signalstack(s *stack) {
- var st sigaltstackt
+ var st, oldst sigaltstackt
+ sigaltstack(nil, &oldst)
+ if oldst.ss_flags & _SS_ONSTACK != 0 {
+ if s != nil {
+ s.lo = uintptr(unsafe.Pointer(oldst.ss_sp))
+ s.hi = s.lo + oldst.ss_size
+ }
+ return
+ }
if s == nil {
st.ss_flags = _SS_DISABLE
} else {
diff --git a/src/runtime/os2_linux.go b/src/runtime/os2_linux.go
index 71f36eb..6ce5e40 100644
--- a/src/runtime/os2_linux.go
+++ b/src/runtime/os2_linux.go
@@ -5,6 +5,7 @@
package runtime
const (
+ _SS_ONSTACK = 1
_SS_DISABLE = 2
_NSIG = 65
_SI_USER = 0However, When I run these ones with gdb, I can get various kinds of strange error messages. Could you please look on this? |
rsc
changed the title
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CL https://golang.org/cl/17903 mentions this issue. |
…dlers Only install signal handlers for synchronous signals that become run-time panics. Set the SA_ONSTACK flag for other signal handlers as needed. Fixes #13028. Update #12465. Update #13034. Update #13042. Change-Id: I28375e70641f60630e10f3c86e24b6e4f8a35cc9 Reviewed-on: https://go-review.googlesource.com/17903 Reviewed-by: Russ Cox <rsc@golang.org> Run-TryBot: Ian Lance Taylor <iant@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org>
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Guys, I have the same problem with LD_PRELOAD firefox, google-chrome and some other programs. Is there any solution for that? I appreciate your response in advance. |
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I'm trying to make my own LD_PRELOAD-able library like this:
This
example.soworks well with several simple programs such asls,cat,cpand so on.However, some programs such as
firefox,google-chrome,gdbget segfault immediately (or sometimes just get hung up).I suspect this is a bug of the Go runtime.
Anyone can please look on this?
Note that C-implementation seems working well with any program:
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