cmd/cgo: make the gccgo init function no_split_stack

This works around what appears to be a bug in current clang (2018-11-09).
Details are in the comment in the code.

Change-Id: Ib4783b6c03d531c69ebc4cb0ac023bea5bee7d40
Reviewed-on: https://go-review.googlesource.com/c/148819
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

diff --git a/src/cmd/cgo/out.go b/src/cmd/cgo/out.go
index a93ff365b019cc3a4bb96c688323507d4ebd05d6..c203873b130841da420dd750142dd1e93574c43a 100644 (file)
--- a/src/cmd/cgo/out.go
+++ b/src/cmd/cgo/out.go
@@ -246,7 +246,22 @@ func (p *Package) writeDefs() {
 
        init := gccgoInit.String()
        if init != "" {
-               fmt.Fprintln(fc, "static void init(void) __attribute__ ((constructor));")
+               // The init function does nothing but simple
+               // assignments, so it won't use much stack space, so
+               // it's OK to not split the stack. Splitting the stack
+               // can run into a bug in clang (as of 2018-11-09):
+               // this is a leaf function, and when clang sees a leaf
+               // function it won't emit the split stack prologue for
+               // the function. However, if this function refers to a
+               // non-split-stack function, which will happen if the
+               // cgo code refers to a C function not compiled with
+               // -fsplit-stack, then the linker will think that it
+               // needs to adjust the split stack prologue, but there
+               // won't be one. Marking the function explicitly
+               // no_split_stack works around this problem by telling
+               // the linker that it's OK if there is no split stack
+               // prologue.
+               fmt.Fprintln(fc, "static void init(void) __attribute__ ((constructor, no_split_stack));")
                fmt.Fprintln(fc, "static void init(void) {")
                fmt.Fprint(fc, init)
                fmt.Fprintln(fc, "}")