From c47cdfa66fe38cfad268615e093969bb136bae07 Mon Sep 17 00:00:00 2001
From: Ayke van Laethem <aykevanlaethem@gmail.com>
Date: Thu, 15 Apr 2021 23:04:05 +0200
Subject: [PATCH] runtime: implement environment variables for Linux

---
 main_test.go                |  2 +-
 src/runtime/runtime.go      |  5 -----
 src/runtime/runtime_unix.go | 34 ++++++++++++++++++++++++++++++++++
 testdata/env.go             |  6 +++---
 testdata/env.txt            |  4 ++--
 5 files changed, 40 insertions(+), 11 deletions(-)

diff --git a/main_test.go b/main_test.go
index 69fe99e6..c9b02ba8 100644
--- a/main_test.go
+++ b/main_test.go
@@ -163,7 +163,7 @@ func runPlatTests(target string, tests []string, t *testing.T) {
 			runTest(name, target, t, nil)
 		})
 	}
-	if target == "wasi" || target == "" && runtime.GOOS == "darwin" {
+	if target == "wasi" || target == "" {
 		t.Run("filesystem.go", func(t *testing.T) {
 			t.Parallel()
 			runTest("filesystem.go", target, t, nil)
diff --git a/src/runtime/runtime.go b/src/runtime/runtime.go
index c648e4f2..1bc09ce0 100644
--- a/src/runtime/runtime.go
+++ b/src/runtime/runtime.go
@@ -89,8 +89,3 @@ func AdjustTimeOffset(offset int64) {
 func os_sigpipe() {
 	runtimePanic("too many writes on closed pipe")
 }
-
-//go:linkname syscall_runtime_envs syscall.runtime_envs
-func syscall_runtime_envs() []string {
-	return nil
-}
diff --git a/src/runtime/runtime_unix.go b/src/runtime/runtime_unix.go
index 17940f69..c0a0ec63 100644
--- a/src/runtime/runtime_unix.go
+++ b/src/runtime/runtime_unix.go
@@ -62,6 +62,40 @@ func runMain() {
 	run()
 }
 
+//go:extern environ
+var environ *unsafe.Pointer
+
+//export strlen
+func strlen(ptr unsafe.Pointer) uintptr
+
+//go:linkname syscall_runtime_envs syscall.runtime_envs
+func syscall_runtime_envs() []string {
+	// Count how many environment variables there are.
+	env := environ
+	numEnvs := 0
+	for *env != nil {
+		numEnvs++
+		env = (*unsafe.Pointer)(unsafe.Pointer(uintptr(unsafe.Pointer(env)) + unsafe.Sizeof(environ)))
+	}
+
+	// Create a string slice of all environment variables.
+	// This requires just a single heap allocation.
+	env = environ
+	envs := make([]string, 0, numEnvs)
+	for *env != nil {
+		ptr := *env
+		length := strlen(ptr)
+		s := _string{
+			ptr:    (*byte)(ptr),
+			length: length,
+		}
+		envs = append(envs, *(*string)(unsafe.Pointer(&s)))
+		env = (*unsafe.Pointer)(unsafe.Pointer(uintptr(unsafe.Pointer(env)) + unsafe.Sizeof(environ)))
+	}
+
+	return envs
+}
+
 func putchar(c byte) {
 	_putchar(int(c))
 }
diff --git a/testdata/env.go b/testdata/env.go
index 7aa5772c..74d27194 100644
--- a/testdata/env.go
+++ b/testdata/env.go
@@ -5,10 +5,10 @@ import (
 )
 
 func main() {
-	println(os.Getenv("ENV1"))
+	println("ENV1:", os.Getenv("ENV1"))
 	v, ok := os.LookupEnv("ENV2")
 	if !ok {
-		panic("ENV2 not found")
+		println("ENV2 not found")
 	}
-	println(v)
+	println("ENV2:", v)
 }
diff --git a/testdata/env.txt b/testdata/env.txt
index d12475f4..7aadfb7b 100644
--- a/testdata/env.txt
+++ b/testdata/env.txt
@@ -1,2 +1,2 @@
-VALUE1
-VALUE2
+ENV1: VALUE1
+ENV2: VALUE2