libgo patch committed: Synchronize empty struct field handling
Commit Message
This libgo patch by Funan Zeng synchronizes the handling of empty
struct fields between the Go frontend and the libgo FFI code. In the
compiler the logic for allocating one byte for the last field of a
struct is:
1. the last field has zero size
2. the struct itself does not have zero size
3. the last field is not blank
This patch adds the last two conditions to runtime.structToFFI. This
is for https://go.dev/issue/55146. Bootstrapped and ran Go testsuite
on x86_64-pc-linux-gnu. Committed to mainline.
Ian
085bacba3502ff77c70a7660c19a68f50e9b7877
@@ -1,4 +1,4 @@
-42efec8c126cf3787bc7c89d9c7f224eff7c5a21
+0140cca9bc0fad1108c7ed369376ac71cc4bfecf
The first line of this file holds the git revision number of the last
merge done from the gofrontend repository.
@@ -4,6 +4,7 @@
// Only build this file if libffi is supported.
+//go:build libffi
// +build libffi
package runtime
@@ -221,9 +222,6 @@ func stringToFFI() *__ffi_type {
// structToFFI returns an ffi_type for a Go struct type.
func structToFFI(typ *structtype) *__ffi_type {
c := len(typ.fields)
- if c == 0 {
- return emptyStructToFFI()
- }
if typ.typ.kind&kindDirectIface != 0 {
return ffi_type_pointer()
}
@@ -231,6 +229,7 @@ func structToFFI(typ *structtype) *__ffi_type {
fields := make([]*__ffi_type, 0, c+1)
checkPad := false
lastzero := false
+ sawnonzero := false
for i, v := range typ.fields {
// Skip zero-sized fields; they confuse libffi,
// and there is no value to pass in any case.
@@ -239,10 +238,13 @@ func structToFFI(typ *structtype) *__ffi_type {
// next field.
if v.typ.size == 0 {
checkPad = true
- lastzero = true
+ if v.name == nil || *v.name != "_" {
+ lastzero = true
+ }
continue
}
lastzero = false
+ sawnonzero = true
if checkPad {
off := uintptr(0)
@@ -263,6 +265,10 @@ func structToFFI(typ *structtype) *__ffi_type {
fields = append(fields, typeToFFI(v.typ))
}
+ if !sawnonzero {
+ return emptyStructToFFI()
+ }
+
if lastzero {
// The compiler adds one byte padding to non-empty struct ending
// with a zero-sized field (types.cc:get_backend_struct_fields).