zig

commit 1690b35770a97aec4b8a7b1b31a61b01e04f5656 (tree)
parent 22b4c9e1a9595bd94ada4c500a430e2668ffcd07
Author: LemonBoy <thatlemon@gmail.com>
Date:   Sat, 23 Oct 2021 10:20:57 +0200

std: Fix edge case in TLS tp calculation

The TLS area may be located in the upper part of the address space and,
if the platform expects a constant offset to be applied, may make the tp
register calculation overflow.

Use +% instead of +, the overflow is harmless.

Diffstat:
M
lib/std/os/linux/tls.zig
 | 
6
++++--

1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/lib/std/os/linux/tls.zig b/lib/std/os/linux/tls.zig
@@ -289,8 +289,10 @@ pub fn prepareTLS(area: []u8) usize {
     // Copy the data
     mem.copy(u8, area[tls_image.data_offset..], tls_image.init_data);
 
-    // Return the corrected (if needed) value for the tp register
-    return @ptrToInt(area.ptr) + tls_tp_offset +
+    // Return the corrected value (if needed) for the tp register.
+    // Overflow here is not a problem, the pointer arithmetic involving the tp
+    // is done with wrapping semantics.
+    return @ptrToInt(area.ptr) +% tls_tp_offset +%
         if (tls_tp_points_past_tcb) tls_image.data_offset else tls_image.tcb_offset;
 }