RE: Buggy commit tracked to: "Re: [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c"

David Laight
2020-10-22T09:33:18Z

From: David Hildenbrand
> Sent: 22 October 2020 10:25
...
> ... especially because I recall that clang and gcc behave slightly
> differently:
>
> https://github.com/hjl-tools/x86-psABI/issues/2
>
> "Function args are different: narrow types are sign or zero extended to
> 32 bits, depending on their type. clang depends on this for incoming
> args, but gcc doesn't make that assumption. But both compilers do it
> when calling, so gcc code can call clang code.

It really is best to use 'int' (or even 'long') for all numeric
arguments (and results) regardless of the domain of the value.

Related, I've always worried about 'bool'....

> The upper 32 bits of registers are always undefined garbage for types
> smaller than 64 bits."

On x86-64 the high bits are zeroed by all 32bit loads.

David

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