[-- Attachment #1: Type: text/plain, Size: 515 bytes --] 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 [-- Attachment #2: patch.txt --] [-- Type: text/plain, Size: 1958 bytes --] 085bacba3502ff77c70a7660c19a68f50e9b7877 diff --git a/gcc/go/gofrontend/MERGE b/gcc/go/gofrontend/MERGE index f7a7985287d..73aa712dbdf 100644 --- a/gcc/go/gofrontend/MERGE +++ b/gcc/go/gofrontend/MERGE @@ -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. diff --git a/libgo/go/runtime/ffi.go b/libgo/go/runtime/ffi.go index cd8479ef551..86ce5b85d04 100644 --- a/libgo/go/runtime/ffi.go +++ b/libgo/go/runtime/ffi.go @@ -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).