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Date: Thu, 20 May 2021 15:12:03 +1000
From: Nicholas Piggin <npiggin@...il.com>
To: "Dmitry V. Levin" <ldv@...linux.org>
Cc: Joakim Tjernlund <Joakim.Tjernlund@...inera.com>,
libc-alpha@...rceware.org, libc-dev@...ts.llvm.org, linux-api@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org, Michael Ellerman <mpe@...erman.id.au>,
Matheus Castanho <msc@...ux.ibm.com>, musl@...ts.openwall.com
Subject: Re: Linux powerpc new system call instruction and ABI
Excerpts from Dmitry V. Levin's message of May 20, 2021 1:06 pm:
> On Thu, May 20, 2021 at 12:40:36PM +1000, Nicholas Piggin wrote:
> [...]
>> > Looks like struct pt_regs.trap already contains the information that could
>> > be used to tell 'sc' from 'scv': if (pt_regs.trap & ~0xf) == 0x3000, then
>> > it's scv. Is my reading of arch/powerpc/include/asm/ptrace.h correct?
>>
>> Hmm, I think it is. Certainly in the kernel regs struct it is, I had in
>> my mind that we put it to 0xc00 when populating the user struct for
>> compatibility, but it seems not. So I guess this would work.
>
> OK, can we state that (pt_regs.trap & ~0xf) == 0x3000 is a part of the scv
> ABI, so it's not going to change and could be relied upon by userspace?
> Could this be documented in Documentation/powerpc/syscall64-abi.rst,
> please?
Yeah I think we can do that. The kernel doesn't care what is put in the
userspace pt_regs.trap too much so if this is your preferred approach
then I will document it in the ABI.
Thanks,
Nick
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