std: align(16) main_thread_tls_buffer

andrewrk · andrewrk · commit f6d6709fe31f · 2020-12-17T22:40:53.000-07:00
Before this change, thread local variables were landmines if LLVM
decided to optimize any writes to them using vector instructions.
diff --git a/lib/std/os/linux/tls.zig b/lib/std/os/linux/tls.zig
@@ -327,7 +327,7 @@ pub fn prepareTLS(area: []u8) usize {
         if (tls_tp_points_past_tcb) tls_image.data_offset else tls_image.tcb_offset;
 }
 
-var main_thread_tls_buffer: [256]u8 = undefined;
+var main_thread_tls_buffer: [256]u8 align(16) = undefined;
 
 pub fn initStaticTLS() void {
     initTLS();

Original file line number	Diff line number	Diff line change
`@@ -327,7 +327,7 @@ pub fn prepareTLS(area: []u8) usize {`
`327`	`327`	`if (tls_tp_points_past_tcb) tls_image.data_offset else tls_image.tcb_offset;`
`328`	`328`	`}`
`329`	`329`
`330`		`-var main_thread_tls_buffer: [256]u8 = undefined;`
	`330`	`+var main_thread_tls_buffer: [256]u8 align(16) = undefined;`
`331`	`331`
`332`	`332`	`pub fn initStaticTLS() void {`
`333`	`333`	`initTLS();`