runtime: align ucontext_t argument to 16 byte boundary

    
    Some systems, such as ia64 and PPC, require that a ucontext_t pointer
    passed to getcontext and friends be aligned to a 16-byte boundary.
    Currently the ucontext_t fields in the g structure are defined in Go,
    and Go has no way to ensure a 16-byte alignment for a struct field.
    The fields are currently represented by an array of unsafe.Pointer.
    Enforce the alignment by making the array larger, and picking an offset
    into the array that is 16-byte aligned.
    
    Reviewed-on: https://go-review.googlesource.com/28910

From-SVN: r240044

1 files changed, 5 insertions, 1 deletions

diff --git a/libgo/go/runtime/runtime2.go b/libgo/go/runtime/runtime2.go
index 05ce513..468d11e 100644
--- a/libgo/go/runtime/runtime2.go
+++ b/libgo/go/runtime/runtime2.go
@@ -805,7 +805,11 @@ var (
 
 // _ucontext_t is a Go version of the C ucontext_t type, used by getcontext.
 // _sizeof_ucontext_t is defined by the Makefile from <ucontext.h>.
-type _ucontext_t [_sizeof_ucontext_t / unsafe.Sizeof(uintptr(0))]unsafe.Pointer
+// On some systems getcontext and friends require a value that is
+// aligned to a 16-byte boundary.  We implement this by increasing the
+// required size and picking an appropriate offset when we use the
+// array.
+type _ucontext_t [(_sizeof_ucontext_t + 15) / unsafe.Sizeof(unsafe.Pointer(nil))]unsafe.Pointer
 
 // traceback is used to collect stack traces from other goroutines.
 type traceback struct {