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SubjectRe: [PATCH v3 1/4] x86/syscall: sign-extend system calls on entry to int

* H. Peter Anvin <> wrote:

> This is an ABI change, but is in fact a revert to the original x86-64
> ABI. The original assembly entry code would zero-extend the system
> call number; this patch uses sign extend to be explicit that this is
> treated as a signed number (although in practice it makes no
> difference, of course) and to avoid people getting the idea of
> "optimizing" it, as has happened on at least two(!) separate
> occasions.

The original x86-64 ABI as documented by AMD, as we (probably) never had
this in Linux, right?

Sounds sensible to do this, assuming nothing relies on the weirdness.



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