Backport PRs to beta #36433
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Backport PRs to beta #36433
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This fixes rust-lang#35849, a regression introduced by the typeck refactoring around TyNever/!.
The memrchr fallback did not compute the offset correctly. It was
intentioned to land on usize-aligned addresses but did not.
This was suspected to resulted in a crash on ARMv7 platform!
This bug affected non-linux platforms.
I think like this, if we have a slice with pointer `ptr` and length
`len`, we want to find the last usize-aligned offset in the slice.
The correct computation should be:
For example if ptr = 1 and len = 6, and size_of::<usize>() is 4:
[ x x x x x x ]
1 2 3 4 5 6
^-- last aligned address at offset 3 from the start.
The last aligned address is ptr + len - (ptr + len) % usize_size.
Compute offset from the start as:
offset = len - (ptr + len) % usize_size = 6 - (1 + 6) % 4 = 6 - 3 = 3.
I believe the function's return value was always correct previously, if
the platform supported unaligned addresses.
This makes the critical calculation easier to understand.
|
r? @brson (rust_highfive has picked a reviewer for you, use r? to override) |
pmatos
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Sep 27, 2016
Backport PRs to beta
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Backporting a few beta-accepted PRs to beta: