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std: Fix edge case in TLS tp calculation

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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.
This commit is contained in:
LemonBoy 2021-10-23 10:20:57 +02:00 committed by Andrew Kelley
parent 22b4c9e1a9
commit 1690b35770
1 changed files with 4 additions and 2 deletions
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6
lib/std/os/linux/tls.zig
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@ -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;
}