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Date: Sun, 16 May 2021 09:48:19 +0200 From: Ingo Molnar <mingo@...nel.org> To: "H. Peter Anvin" <hpa@...or.com> Cc: Ingo Molnar <mingo@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...en8.de>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v3 1/4] x86/syscall: sign-extend system calls on entry to int * H. Peter Anvin <hpa@...or.com> 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. Thanks, Ingo
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