cmd/cgo: definition of GoString is incorrect for exported functions #5548
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from the go-nuts thread on the subject: if the code is modified to http://play.golang.org/p/J6fUEF4E_9, then the function works just fine, but if we replace strlen(t) on line 10 with the value it returns, 6, the resulting program crashes again. putting a panic() inside hello_from_c in main.go gives this interesting observation: with strlen(t): main.hello_from_c(0x40680b5, 0x6, 0x2a) cgotest/_obj/main.cgo1.go:17 +0x119 with "6" instead: [fp=0x41d1e30] main.hello_from_c(0x40680bd, 0x7fff00000006, 0x2a) cgotest/_obj/main.cgo1.go:16 +0xdd |
Ian Lance Taylor:
I see the bug. _cgo_export.c looks like this:
void hello_from_c(GoString p0, GoInt p1)
{
struct {
GoString p0;
GoInt p1;
} __attribute__((packed)) a;
a.p0 = p0;
a.p1 = p1;
crosscall2(_cgoexp_44bb5d457081_hello_from_c, &a, 24);
}
_cgo_export.h has this:
typedef struct { char *p; int n; } GoString;
This means that the generated hello_from_c code is going to convert
from GoInt to int when setting the string length of p0. That will
break if it so happens that the upper 32 bits of the string length are
not already zero.
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Labels changed: added priority-soon, go1.1.1, removed priority-triage. Owner changed to @ianlancetaylor. Status changed to Accepted. |
https://golang.org/cl/9643044 Status changed to Started. |
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This issue was closed by revision 8f7863d. Status changed to Fixed. |
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Issue #5646 has been merged into this issue. |
This issue was closed.
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$ go version go version devel +45468e9eae1f Wed May 22 18:51:15 2013 +0800 darwin/amd64 What steps will reproduce the problem? Following Minux's suggested steps: $ mkdir -p /tmp/gopath/src/cgotest $ cd /tmp/gopath/src/cgotest $ cat > main.go <<EOF package main import ( "fmt" "unsafe" ) /* #include <stdlib.h> void my_printf(char* str); */ import "C" //export hello_from_c func hello_from_c(s string, i int) { fmt.Printf("From C: %s, %d\n", s, i) } func main() { cstr := C.CString("GoTest") defer C.free(unsafe.Pointer(cstr)) C.my_printf(cstr) } EOF $ cat > part.c <<EOF #include <_cgo_export.h> #include <stdio.h> void my_printf(char *s){ printf("From Go: %s\n", s); GoString d; d.p = "C Test"; d.n = 7; // printf("C STRING: %s\n", d.p); // fflush(stdout); hello_from_c(d, 42); } EOF $ GOPATH=/tmp/gopath go install cgotest $ /tmp/gopath/bin/cgotest What is the expected output? From Go: GoTest From C: C Test, 42 What do you see instead? http://play.golang.org/p/QsokZKHkRr Which operating system are you using? OSXThe text was updated successfully, but these errors were encountered: