runtime: implement getenv for Plan 9

With this change the runtime can now read GOMAXPROCS, GOGC, etc.

I'm not quite sure how we missed this.

R=seed, lucio.dere, rsc
CC=golang-dev
https://golang.org/cl/6935062

src/pkg/runtime/env_plan9.c

+// Copyright 2012 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.
+
+#include "runtime.h"
+#include "os_GOOS.h"
+
+byte*
+runtime·getenv(int8 *s)
+{
+	int32 fd, len, n, r;
+	byte file[128];
+	byte *p;
+
+	len = runtime·findnull((byte*)s);
+	if(len > sizeof file-6)
+		return nil;
+
+	runtime·memclr(file, sizeof file);
+	runtime·memmove((void*)file, (void*)"/env/", 5);
+	runtime·memmove((void*)(file+5), (void*)s, len);
+
+	fd = runtime·open(file, OREAD);
+	if(fd < 0)
+		return nil;
+	n = runtime·seek(fd, 0, 2);
+	p = runtime·malloc(n+1);
+	r = runtime·pread(fd, p, n, 0);
+	runtime·close(fd);
+	if(r < 0)
+		return nil;
+	return p;
+}

src/pkg/runtime/env_posix.c

+// Copyright 2012 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.
+
+// +build darwin freebsd linux netbsd openbsd windows
+
+#include "runtime.h"
+
+Slice syscall·envs;
+
+byte*
+runtime·getenv(int8 *s)
+{
+	int32 i, j, len;
+	byte *v, *bs;
+	String* envv;
+	int32 envc;
+
+	bs = (byte*)s;
+	len = runtime·findnull(bs);
+	envv = (String*)syscall·envs.array;
+	envc = syscall·envs.len;
+	for(i=0; i<envc; i++){
+		if(envv[i].len <= len)
+			continue;
+		v = envv[i].str;
+		for(j=0; j<len; j++)
+			if(bs[j] != v[j])
+				goto nomatch;
+		if(v[len] != '=')
+			goto nomatch;
+		return v+len+1;
+	nomatch:;
+	}
+	return nil;
+}
+
+void (*libcgo_setenv)(byte**);
+
+// Update the C environment if cgo is loaded.
+// Called from syscall.Setenv.
+void
+syscall·setenv_c(String k, String v)
+{
+	byte *arg[2];
+
+	if(libcgo_setenv == nil)
+		return;
+
+	arg[0] = runtime·malloc(k.len + 1);
+	runtime·memmove(arg[0], k.str, k.len);
+	arg[0][k.len] = 0;
+
+	arg[1] = runtime·malloc(v.len + 1);
+	runtime·memmove(arg[1], v.str, v.len);
+	arg[1][v.len] = 0;
+
+	runtime·asmcgocall((void*)libcgo_setenv, arg);
+	runtime·free(arg[0]);
+	runtime·free(arg[1]);
+}

src/pkg/runtime/os_plan9.h

@@ -7,6 +7,7 @@ int32	runtime·open(uint8 *file, int32 mode);
 int32	runtime·pread(int32 fd, void *buf, int32 nbytes, int64 offset);
 int32	runtime·pwrite(int32 fd, void *buf, int32 nbytes, int64 offset);
 int32	runtime·read(int32 fd, void *buf, int32 nbytes);
+int64	runtime·seek(int32 fd, int64 offset, int32 whence);
 int32	runtime·close(int32 fd);
 void	runtime·exits(int8* msg);
 intptr	runtime·brk_(void*);

src/pkg/runtime/runtime.c

@@ -110,58 +110,6 @@ runtime·goenvs_unix(void)
 	syscall·envs.cap = n;
 }
 
-byte*
-runtime·getenv(int8 *s)
-{
-	int32 i, j, len;
-	byte *v, *bs;
-	String* envv;
-	int32 envc;
-
-	bs = (byte*)s;
-	len = runtime·findnull(bs);
-	envv = (String*)syscall·envs.array;
-	envc = syscall·envs.len;
-	for(i=0; i<envc; i++){
-		if(envv[i].len <= len)
-			continue;
-		v = envv[i].str;
-		for(j=0; j<len; j++)
-			if(bs[j] != v[j])
-				goto nomatch;
-		if(v[len] != '=')
-			goto nomatch;
-		return v+len+1;
-	nomatch:;
-	}
-	return nil;
-}
-
-void (*libcgo_setenv)(byte**);
-
-// Update the C environment if cgo is loaded.
-// Called from syscall.Setenv.
-void
-syscall·setenv_c(String k, String v)
-{
-	byte *arg[2];
-
-	if(libcgo_setenv == nil)
-		return;
-
-	arg[0] = runtime·malloc(k.len + 1);
-	runtime·memmove(arg[0], k.str, k.len);
-	arg[0][k.len] = 0;
-
-	arg[1] = runtime·malloc(v.len + 1);
-	runtime·memmove(arg[1], v.str, v.len);
-	arg[1][v.len] = 0;
-
-	runtime·asmcgocall((void*)libcgo_setenv, arg);
-	runtime·free(arg[0]);
-	runtime·free(arg[1]);
-}
-
 void
 runtime·getgoroot(String out)
 {

src/pkg/runtime/sys_plan9_386.s

@@ -24,9 +24,19 @@ TEXT runtime·pwrite(SB),7,$0
 	INT     $64
 	RET
 
+TEXT runtime·seek(SB),7,$0
+	MOVL	$39, AX
+	INT	$64
+	CMPL	AX, $-1
+	JNE	4(PC)
+	MOVL	a+0(FP), CX
+	MOVL	AX, 0(CX)
+	MOVL	AX, 4(CX)
+	RET
+
 TEXT runtime·close(SB),7,$0
 	MOVL	$4, AX
-	INT		$64
+	INT	$64
 	RET
 
 TEXT runtime·exits(SB),7,$0

src/pkg/runtime/sys_plan9_amd64.s

@@ -27,6 +27,30 @@ TEXT runtime·pwrite(SB),7,$0
 	SYSCALL
 	RET
 
+// int32 _seek(int64*, int32, int64, int32)
+TEXT _seek<>(SB),7,$0
+	MOVQ	$0x8000, AX
+	MOVQ	$39, BP
+	SYSCALL
+	RET
+
+// int64 seek(int32, int64, int32)
+TEXT runtime·seek(SB),7,$56
+	LEAQ	new+48(SP), CX
+	MOVQ	CX, 0(SP)
+	MOVQ	fd+0(FP), CX
+	MOVQ	CX, 8(SP)
+	MOVQ	off+8(FP), CX
+	MOVQ	CX, 16(SP)
+	MOVQ	whence+16(FP), CX
+	MOVQ	CX, 24(SP)
+	CALL	_seek<>(SB)
+	CMPL	AX, $0
+	JGE	2(PC)
+	MOVQ	$-1, new+48(SP)
+	MOVQ	new+48(SP), AX
+	RET
+
 TEXT runtime·close(SB),7,$0
 	MOVQ	$0x8000, AX
 	MOVQ	$4, BP