From 7e63f7ad0311c80bcec89649d723af8a97935ba2 Mon Sep 17 00:00:00 2001
From: Andreas Linz <klingt.net@gmail.com>
Date: Wed, 23 Dec 2020 10:16:27 +0100
Subject: [PATCH] Truncate user and group ids for 64 bit Linux systems (#7466)

* Truncate user and group ids

Calls to `getuid`, `getgid` and their `eid` variants fail to compile on
64bit Linux systems because the return value of the syscall is of
`usize` and needs to be truncated to fit the size of `uid_t` that is 32
bit.

Thanks to @FireFox317 for figuring this out in Zig's Discord channel!

* Add a regression test for user and group ids

* Replace @truncate with @intCast

This should be safe because `uid_t` will be 32-bit.

* Add missing import for getauxval

* Add missing package names

* Revert "Add missing import for getauxval"

This reverts commit 38f93dc89effdf657f2b81a56b96527ce4083f52.

* Skip user and group test if builtin.link_libc
---
 lib/std/os/linux.zig      | 16 ++++++++--------
 lib/std/os/linux/test.zig |  9 +++++++++
 2 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/lib/std/os/linux.zig b/lib/std/os/linux.zig
index f252a08fc9..d3fffd231e 100644
--- a/lib/std/os/linux.zig
+++ b/lib/std/os/linux.zig
@@ -745,33 +745,33 @@ pub fn setregid(rgid: gid_t, egid: gid_t) usize {
 
 pub fn getuid() uid_t {
     if (@hasField(SYS, "getuid32")) {
-        return @as(uid_t, syscall0(.getuid32));
+        return @intCast(uid_t, syscall0(.getuid32));
     } else {
-        return @as(uid_t, syscall0(.getuid));
+        return @intCast(uid_t, syscall0(.getuid));
     }
 }
 
 pub fn getgid() gid_t {
     if (@hasField(SYS, "getgid32")) {
-        return @as(gid_t, syscall0(.getgid32));
+        return @intCast(gid_t, syscall0(.getgid32));
     } else {
-        return @as(gid_t, syscall0(.getgid));
+        return @intCast(gid_t, syscall0(.getgid));
     }
 }
 
 pub fn geteuid() uid_t {
     if (@hasField(SYS, "geteuid32")) {
-        return @as(uid_t, syscall0(.geteuid32));
+        return @intCast(uid_t, syscall0(.geteuid32));
     } else {
-        return @as(uid_t, syscall0(.geteuid));
+        return @intCast(uid_t, syscall0(.geteuid));
     }
 }
 
 pub fn getegid() gid_t {
     if (@hasField(SYS, "getegid32")) {
-        return @as(gid_t, syscall0(.getegid32));
+        return @intCast(gid_t, syscall0(.getegid32));
     } else {
-        return @as(gid_t, syscall0(.getegid));
+        return @intCast(gid_t, syscall0(.getegid));
     }
 }
 
diff --git a/lib/std/os/linux/test.zig b/lib/std/os/linux/test.zig
index 7b3840288a..0077fbcee4 100644
--- a/lib/std/os/linux/test.zig
+++ b/lib/std/os/linux/test.zig
@@ -9,6 +9,7 @@ const linux = std.os.linux;
 const mem = std.mem;
 const elf = std.elf;
 const expect = std.testing.expect;
+const expectEqual = std.testing.expectEqual;
 const fs = std.fs;
 
 test "fallocate" {
@@ -99,3 +100,11 @@ test "statx" {
     expect(@bitCast(u64, @as(i64, stat_buf.blksize)) == statx_buf.blksize);
     expect(@bitCast(u64, @as(i64, stat_buf.blocks)) == statx_buf.blocks);
 }
+
+test "user and group ids" {
+    if (builtin.link_libc) return error.SkipZigTest;
+    expectEqual(linux.getauxval(elf.AT_UID), linux.getuid());
+    expectEqual(linux.getauxval(elf.AT_GID), linux.getgid());
+    expectEqual(linux.getauxval(elf.AT_EUID), linux.geteuid());
+    expectEqual(linux.getauxval(elf.AT_EGID), linux.getegid());
+}