From: Peter Zijlstra <peterz@infradead.org>
To: Sven Schnelle <svens@linux.ibm.com>
Cc: "Thomas Gleixner" <tglx@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
"Michal Suchánek" <msuchanek@suse.de>,
"Jonathan Corbet" <corbet@lwn.net>,
"Shuah Khan" <skhan@linuxfoundation.org>,
"Huacai Chen" <chenhuacai@kernel.org>,
"WANG Xuerui" <kernel@xen0n.name>,
"Madhavan Srinivasan" <maddy@linux.ibm.com>,
"Michael Ellerman" <mpe@ellerman.id.au>,
"Nicholas Piggin" <npiggin@gmail.com>,
"Christophe Leroy (CS GROUP)" <chleroy@kernel.org>,
"Paul Walmsley" <pjw@kernel.org>,
"Palmer Dabbelt" <palmer@dabbelt.com>,
"Albert Ou" <aou@eecs.berkeley.edu>,
"Alexandre Ghiti" <alex@ghiti.fr>,
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"Alexander Gordeev" <agordeev@linux.ibm.com>,
"Christian Borntraeger" <borntraeger@linux.ibm.com>,
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"Borislav Petkov" <bp@alien8.de>,
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x86@kernel.org,
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"Deepak Gupta" <debug@rivosinc.com>,
"Lukas Gerlach" <lukas.gerlach@cispa.de>,
"Rui Qi" <qirui.001@bytedance.com>, "Kees Cook" <kees@kernel.org>,
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loongarch@lists.linux.dev, linuxppc-dev@lists.ozlabs.org,
linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org
Subject: Re: [RFC] entry: Untangle the return value of syscall_enter_from_user_mode from syscall NR
Date: Fri, 3 Jul 2026 11:25:44 +0200 [thread overview]
Message-ID: <20260703092544.GB651302@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <yt9dwlvca8rn.fsf@linux.ibm.com>
On Fri, Jul 03, 2026 at 08:26:36AM +0200, Sven Schnelle wrote:
> The difference between x86 and s390 is that on s390, regs->gprs[2] is
> used for both the syscall number and the syscall return value.
> That was a design mistake early in the begin about 25 years ago, but
> it's ABI now, so it cannot be changed.
>
> When seccomp decides to skip a syscall, it write a return value into
> regs->gprs[2]. When syscall_enter_from_user_mode_work() returns, it
> returns this number. If it's negative all is good - the 'if (likely(nr <
> NR_syscalls))' conditiion would just catch it and skip the syscall.
You do have regs->orig_gpr2; I didn't fully track its usage, but can't
you treat that as the syscall nr and always consider regs->gprs[2] as the
return value?
next prev parent reply other threads:[~2026-07-03 9:26 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-01 17:42 [RFC] entry: Untangle the return value of syscall_enter_from_user_mode from syscall NR Michal Suchánek
2026-07-01 18:29 ` H. Peter Anvin
2026-07-02 9:30 ` Michal Suchánek
2026-07-02 21:49 ` Thomas Gleixner
2026-07-03 6:26 ` Sven Schnelle
2026-07-03 9:25 ` Peter Zijlstra [this message]
2026-07-03 9:27 ` Thomas Gleixner
2026-07-03 9:59 ` Sven Schnelle
2026-07-03 10:57 ` Peter Zijlstra
2026-07-03 11:17 ` Sven Schnelle
2026-07-03 11:25 ` Michal Suchánek
2026-07-03 11:39 ` Sven Schnelle
2026-07-02 8:12 ` Sven Schnelle
2026-07-02 9:12 ` Michal Suchánek
2026-07-02 12:01 ` Sven Schnelle
2026-07-02 12:13 ` Michal Suchánek
2026-07-03 6:16 ` Sven Schnelle
2026-07-02 11:24 ` Thomas Gleixner
2026-07-02 11:45 ` Michal Suchánek
2026-07-02 20:45 ` Thomas Gleixner
2026-07-03 7:53 ` Michal Suchánek
2026-07-03 9:34 ` Thomas Gleixner
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