RE: Buggy commit tracked to: "Re: [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c"
From: David Laight <hidden>
Date: 2020-10-23 13:29:09
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From: Arnd Bergmann
Sent: 23 October 2020 14:23 On Fri, Oct 23, 2020 at 2:46 PM David Laight [off-list ref] wrote:quoted
From: Greg KH <gregkh@linuxfoundation.org>quoted
Sent: 22 October 2020 14:51I've rammed the code into godbolt. https://godbolt.org/z/9v5PPW Definitely a clang bug. Search for [wx]24 in the clang output. nr_segs comes in as w2 and the initial bound checks are done on w2. w24 is loaded from w2 - I don't believe this changes the high bits.You believe wrong, "mov w24, w2" is a zero-extending operation.
Ah ok, but gcc uses utxw for the same task. I guess they could be the same opcode. Last time I wrote ARM thumb didn't really exist - never mind 64bit David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)