syscall, runtime: always call XSI strerror_r

This does the right thing for either glibc or musl on GNU/Linux.

Based on patch by Sören Tempel.

Change-Id: If2969e131f0fae456d58b35d839d8abe191fcc59
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/454176
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Bypass: Ian Lance Taylor <iant@google.com>

libgo/Makefile.am

@@ -465,6 +465,7 @@ runtime_files = \
 	runtime/go-nanotime.c \
 	runtime/go-now.c \
 	runtime/go-nosys.c \
+	runtime/go-strerror.c \
 	runtime/go-reflect-call.c \
 	runtime/go-setenv.c \
 	runtime/go-signal.c \

libgo/Makefile.in

@@ -247,7 +247,7 @@ am__objects_4 = runtime/aeshash.lo runtime/go-assert.lo \
 	runtime/go-fieldtrack.lo runtime/go-matherr.lo \
 	runtime/go-memclr.lo runtime/go-memmove.lo \
 	runtime/go-memequal.lo runtime/go-nanotime.lo \
-	runtime/go-now.lo runtime/go-nosys.lo \
+	runtime/go-now.lo runtime/go-nosys.lo runtime/go-strerror.lo \
 	runtime/go-reflect-call.lo runtime/go-setenv.lo \
 	runtime/go-signal.lo runtime/go-unsafe-pointer.lo \
 	runtime/go-unsetenv.lo runtime/go-unwind.lo \
@@ -917,6 +917,7 @@ runtime_files = \
 	runtime/go-nanotime.c \
 	runtime/go-now.c \
 	runtime/go-nosys.c \
+	runtime/go-strerror.c \
 	runtime/go-reflect-call.c \
 	runtime/go-setenv.c \
 	runtime/go-signal.c \
@@ -1390,6 +1391,8 @@ runtime/go-now.lo: runtime/$(am__dirstamp) \
 	runtime/$(DEPDIR)/$(am__dirstamp)
 runtime/go-nosys.lo: runtime/$(am__dirstamp) \
 	runtime/$(DEPDIR)/$(am__dirstamp)
+runtime/go-strerror.lo: runtime/$(am__dirstamp) \
+	runtime/$(DEPDIR)/$(am__dirstamp)
 runtime/go-reflect-call.lo: runtime/$(am__dirstamp) \
 	runtime/$(DEPDIR)/$(am__dirstamp)
 runtime/go-setenv.lo: runtime/$(am__dirstamp) \
@@ -1457,6 +1460,7 @@ distclean-compile:
 @AMDEP_TRUE@@am__include@ @am__quote@runtime/$(DEPDIR)/go-reflect-call.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@runtime/$(DEPDIR)/go-setenv.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@runtime/$(DEPDIR)/go-signal.Plo@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@runtime/$(DEPDIR)/go-strerror.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@runtime/$(DEPDIR)/go-unsafe-pointer.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@runtime/$(DEPDIR)/go-unsetenv.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@runtime/$(DEPDIR)/go-unwind.Plo@am__quote@

libgo/go/syscall/errstr.go

@@ -4,23 +4,19 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build !hurd && !linux
-// +build !hurd,!linux
-
 package syscall
 
-//sysnb	strerror_r(errnum int, buf []byte) (err Errno)
-//strerror_r(errnum _C_int, buf *byte, buflen Size_t) _C_int
+import "internal/bytealg"
+
+//extern go_strerror
+func go_strerror(_C_int, *byte, Size_t) _C_int
 
 func Errstr(errnum int) string {
-	for len := 128; ; len *= 2 {
-		b := make([]byte, len)
-		errno := strerror_r(errnum, b)
+	for size := 128; ; size *= 2 {
+		b := make([]byte, size)
+		errno := go_strerror(_C_int(errnum), &b[0], Size_t(len(b)))
 		if errno == 0 {
-			i := 0
-			for b[i] != 0 {
-				i++
-			}
+			i := bytealg.IndexByte(b, 0)
 			// Lowercase first letter: Bad -> bad, but
 			// STREAM -> STREAM.
 			if i > 1 && 'A' <= b[0] && b[0] <= 'Z' && 'a' <= b[1] && b[1] <= 'z' {
@@ -29,7 +25,7 @@ func Errstr(errnum int) string {
 			return string(b[:i])
 		}
 		if errno != ERANGE {
-			return "errstr failure"
+			return "strerror_r failure"
 		}
 	}
 }

libgo/runtime/go-strerror.c

@@ -0,0 +1,37 @@
+/* go-strerror.c -- wrapper around XSI-compliant strerror_r.
+
+   Copyright 2022 The Go Authors. All rights reserved.
+   Use of this source code is governed by a BSD-style
+   license that can be found in the LICENSE file.  */
+
+/* There are two version of strerror_r on GNU/Linux: a GNU-specific
+   and an XSI-compliant version.  The former version is only available
+   on glibc.  Since glibc 2.13, the XSI-compliant version is also
+   provided by glibc if _GNU_SOURCE is not defined.  Since the
+   entirety of gofrontend is compiled with _GNU_SOURCE, this file
+   exists to selectively undefine it and provides an alias to the
+   XSI-compliant version of strerror_r(3).  */
+
+#ifdef __linux__
+
+/* Force selection of XSI-compliant strerror_r by glibc.  */
+#undef XOPEN_SOURCE
+#define XOPEN_SOURCE 600
+#undef _POSIX_C_SOURCE
+#define _POSIX_C_SOURCE 200112L
+#undef _GNU_SOURCE
+
+#endif /* __linux__ */
+
+#include <string.h>
+
+#ifndef HAVE_STRERROR_R
+// Provided by go-nosys.c if not provided by libc itself.
+extern int strerror_r (int, char *, size_t);
+#endif
+
+int
+go_strerror (int errnum, char *buf, size_t buflen)
+{
+  return strerror_r (errnum, buf, buflen);
+}