From: Josh Poimboeuf <jpoimboe@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
Mark Rutland <mark.rutland@arm.com>,
Jason Baron <jbaron@akamai.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ard Biesheuvel <ardb@kernel.org>,
Christophe Leroy <christophe.leroy@csgroup.eu>,
Paolo Bonzini <pbonzini@redhat.com>,
Sean Christopherson <seanjc@google.com>,
Sami Tolvanen <samitolvanen@google.com>,
Nick Desaulniers <ndesaulniers@google.com>,
Will McVicker <willmcvicker@google.com>,
Kees Cook <keescook@chromium.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 11/11] static_call: Remove DEFINE_STATIC_CALL_RET0()
Date: Wed, 22 Mar 2023 11:45:18 -0700 [thread overview]
Message-ID: <20230322184518.wjgfp7dyxvg5la5p@treble> (raw)
In-Reply-To: <20230322151532.GG2357380@hirez.programming.kicks-ass.net>
On Wed, Mar 22, 2023 at 04:15:32PM +0100, Peter Zijlstra wrote:
> On Tue, Mar 21, 2023 at 09:00:17PM -0700, Josh Poimboeuf wrote:
> > NULL and RET0 static calls are both slightly different ways of nopping a
> > static call. A not-insignificant amount of code and complexity is spent
> > maintaining them separately. It's also somewhat tricky for the user who
> > has to try to remember to use the correct one for the given function
> > type.
>
> Well, I have very little sympathy for that argument. The return type
> should be a big frigging clue.
>
> > Simplify things all around by just combining them, such that NULL static
> > calls always return 0.
> >
> > While it doesn't necessarily make sense for void-return functions to
> > return 0, it's pretty much harmless. The return value register is
> > already callee-clobbered, and an extra "xor %eax, %eax" shouldn't affect
> > performance (knock on wood).
>
> Urgh.. OTOH I do like the lines removes.
So this patch is more of an RFC than the others. I'm not fully
convinced myself, but I very much liked the removed lines and simpler
interface.
> > This "do nothing return 0" default should work for the vast majority of
> > NULL cases. Otherwise it can be easily overridden with a user-specified
> > function which panics or returns 0xdeadbeef or does whatever one wants.
> >
> > This simplifies the static call code and also tends to help simplify
> > users' code as well.
>
> Can we at least keep the DEFINE_STATIC_CALL_RET0() and
> __static_call_return0 as aliases? It reads really daft to use _NULL or
> __static_call_nop for non-void functions.
I disagree, to me NULL means "nop the function (including any return
value)". Nice and easy.
Keeping those other ret0 defines around would negate some of the cool
deletions.
--
Josh
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prev parent reply other threads:[~2023-03-22 18:46 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-22 4:00 [PATCH v2 00/11] static_call: Improve NULL/ret0 handling Josh Poimboeuf
2023-03-22 4:00 ` [PATCH v2 01/11] static_call: Improve key type abstraction Josh Poimboeuf
2023-03-22 4:53 ` Josh Poimboeuf
2023-03-22 5:02 ` [PATCH v2.1 " Josh Poimboeuf
2023-03-22 4:00 ` [PATCH v2 02/11] static_call: Flip key type union bit Josh Poimboeuf
2023-03-22 5:03 ` [PATCH v2.1 " Josh Poimboeuf
2023-03-22 4:00 ` [PATCH v2 03/11] static_call: Remove static_call_mod_init() declaration Josh Poimboeuf
2023-03-22 4:00 ` [PATCH v2 04/11] static_call: Remove static_call.h dependency on cpu.h Josh Poimboeuf
2023-03-22 4:00 ` [PATCH v2 05/11] static_call: Make ARCH_ADD_TRAMP_KEY() generic Josh Poimboeuf
2023-03-22 4:00 ` [PATCH v2 06/11] static_call: "EXPORT_STATIC_CALL_TRAMP" -> "EXPORT_STATIC_CALL_RO" Josh Poimboeuf
2023-03-22 4:00 ` [PATCH v2 07/11] static_call: Reorganize static call headers Josh Poimboeuf
2023-03-22 4:00 ` [PATCH v2 08/11] arm64/static_call: Fix static call CFI violations Josh Poimboeuf
2023-03-22 12:22 ` Mark Rutland
2023-03-22 14:19 ` Peter Zijlstra
2023-03-22 18:26 ` Josh Poimboeuf
2023-03-22 18:09 ` Josh Poimboeuf
2023-03-22 18:07 ` Sami Tolvanen
2023-03-22 18:33 ` Josh Poimboeuf
2023-03-22 4:00 ` [PATCH v2 09/11] static_call: Make NULL static calls consistent Josh Poimboeuf
2023-03-22 14:45 ` Peter Zijlstra
2023-03-22 14:59 ` Peter Zijlstra
2023-03-22 18:35 ` Josh Poimboeuf
2023-03-22 15:04 ` Christophe Leroy
2023-03-22 4:00 ` [PATCH v2 10/11] static_call: Remove static_call_cond() Josh Poimboeuf
2023-03-22 4:00 ` [PATCH v2 11/11] static_call: Remove DEFINE_STATIC_CALL_RET0() Josh Poimboeuf
2023-03-22 15:04 ` Christophe Leroy
2023-03-22 18:50 ` Josh Poimboeuf
2023-03-22 15:15 ` Peter Zijlstra
2023-03-22 18:45 ` Josh Poimboeuf [this message]
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