runtime: signal handling: cgoSigtramp fails to save C callee-save registers. #18328
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The repro case is a minor variation on the test-case added in change 34239, obtained by making a local variable live across the invocation of the deferred handler: $ diff -u $GOROOT/misc/cgo/testsanitizers/tsan9.go ./issue18328.go
--- /home/bcmills/src/go/misc/cgo/testsanitizers/tsan9.go 2016-12-15 11:54:46.895601246 -0800
+++ ./issue18328.go 2016-12-15 12:40:58.691484523 -0800
@@ -19,10 +19,14 @@
size_t n;
struct timeval tvstart, tvnow;
int diff;
+ void *prev = NULL, *cur;
gettimeofday(&tvstart, NULL);
for (n = 0; n < 1<<20; n++) {
- free(malloc(n));
+ cur = malloc(n);
+ free(prev);
+ prev = cur;
+
gettimeofday(&tvnow, NULL);
diff = (tvnow.tv_sec - tvstart.tv_sec) * 1000 * 1000 + (tvnow.tv_usec - tvstart.tv_usec);
@@ -32,6 +36,8 @@
break;
}
}
+
+ free(prev);
}
*/
import "C" |
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@ianlancetaylor: I'm guessing one of us should fix this. I'm happy to send a patch unless you want to do it yourself. |
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CL https://golang.org/cl/34501 mentions this issue. |
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CL https://golang.org/cl/35068 mentions this issue. |
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Use R11 (a caller-saved temp register) instead of RBX (a callee-saved register). I believe this only affects linux/amd64, since it is the only platform with a non-trivial cgoSigtramp implementation. Updates #18328. Change-Id: I3d35c4512624184d5a8ece653fa09ddf50e079a2 Reviewed-on: https://go-review.googlesource.com/35068 Reviewed-by: Ian Lance Taylor <iant@golang.org> Run-TryBot: Ian Lance Taylor <iant@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org>
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In programs using cgo,
runtime.setsigregistersruntime.cgoSigtrampas the handler for signals to the runtime.cgoSigtrampcallssigtramp, which callssigtrampgo, which uses the Go calling convention. The Go convention treats all registers except the stack pointer and frame pointer as caller-save (#16922).In debugging #17641, I noticed that
cgoSigtrampdoes not save the C callee-save registers before invoking those Go functions. If the call to the Go handler is forwarded through other C handlers (as in the case of TSAN interceptors; see #18255), that potentially results in corruption of the register contents and undefined behavior when control returns to the C caller.I am attempting to write a reproducible test-case and will post it here as an update.
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