Commit 314ce5465dfdc9f4d1e2d178704b47666d541fc4 | zig

author	Andrew Kelley <andrew@ziglang.org> 2022-07-03 22:18:05-07:00
committer	Andrew Kelley <andrew@ziglang.org> 2022-07-03 22:18:05-07:00
log	314ce5465dfdc9f4d1e2d178704b47666d541fc4
tree	6b2d299575d87f405170c74b44fb99e279254a99
parent	5735ce39ae5a9fb2bc2ac9f5a722276c291b28bc

std: better definition for std.os.linux.epoll_event

The previous definition depends on a non-lang-spec-compliant memory
layout for packed structs, which happens to trigger #11989 in stage2.

This commit changes the struct to be an extern struct with an
align(4) field. However, stage1 cannot handle this, so conditional
compilation logic is used to select different struct definitions
depending on stage1 vs stage2.

This works around #11989 but does not solve the underlying problem -
putting an extern union inside a packed struct will still trigger the
assert.

After this, both stage1 and stage2 std lib tests run assertion-clean
with a debug LLVM 13.

1 files changed, 12 insertions(+), 7 deletions(-)

lib
- std
  - os
    linux.zig

lib/std/os/linux.zig+12-7

 @@ -3222,16 +3222,21 @@ pub const epoll_data = extern union {
     @"u64": u64,
 };
-// On x86_64 the structure is packed so that it matches the definition of its
+pub const epoll_event = switch (builtin.zig_backend) {
-// 32bit counterpart
+    // stage1 crashes with the align(4) field so we have this workaround
-pub const epoll_event = switch (native_arch) {
+    .stage1 => switch (native_arch) {
-    .x86_64 => packed struct {
+        .x86_64 => packed struct {
-        events: u32,
+            events: u32,
-        data: epoll_data,
+            data: epoll_data,
+        },
+        else => extern struct {
+            events: u32,
+            data: epoll_data,
+        },
     },
     else => extern struct {
         events: u32,
-        data: epoll_data,
+        data: epoll_data align(4),
     },
 };