From: Borislav Petkov <bp@alien8.de>
To: Vincent MAILHOL <mailhol.vincent@wanadoo.fr>
Cc: Nick Desaulniers <ndesaulniers@google.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
x86@kernel.org, Peter Zijlstra <peterz@infradead.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H . Peter Anvin" <hpa@zytor.com>,
Nathan Chancellor <nathan@kernel.org>, Tom Rix <trix@redhat.com>,
linux-kernel@vger.kernel.org, llvm@lists.linux.dev,
David Howells <dhowells@redhat.com>,
Jan Beulich <JBeulich@suse.com>,
Christophe Jaillet <christophe.jaillet@wanadoo.fr>,
Joe Perches <joe@perches.com>,
Josh Poimboeuf <jpoimboe@kernel.org>
Subject: Re: [PATCH v5 2/2] x86/asm/bitops: __ffs,ffz: use __builtin_ctzl to evaluate constant expressions
Date: Wed, 7 Sep 2022 06:06:58 +0200 [thread overview]
Message-ID: <YxgY2MBmBIkBsdlu@nazgul.tnic> (raw)
In-Reply-To: <CAMZ6RqJSdbbpFw7iZBqmADY0cAhjzFkpqs+VWCfFM_P0P-wH6w@mail.gmail.com>
On Sat, Aug 27, 2022 at 06:32:05AM +0900, Vincent MAILHOL wrote:
> Agree that this is only the surface. But, my patch series is about
> constant folding, not about the text of *ffs(). Here, I just *move*
> the existing text, I did not modify anything.
> Can we agree that this is a separate topic?
Sure we can.
But then you can't start your commit message with:
"__ffs(x) is equivalent to (unsigned long)__builtin_ctzl(x) and ffz(x)
is equivalent to (unsigned long)__builtin_ctzl(~x)."
which will bring unenlightened readers like me into the very same mess.
So at least mention that there's a difference between the kernel
implementation using hw insns which are well defined on some machines
and what the glibc API does. So that at least people are aware that
there's something dangerous to be cautious about.
Ok?
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2022-09-07 4:06 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-11 16:03 [PATCH v2 0/2] x86/asm/bitops: optimize ff{s,z} functions for constant expressions Vincent Mailhol
2022-05-11 16:03 ` [PATCH v2 1/2] x86/asm/bitops: ffs: use __builtin_ffs to evaluate " Vincent Mailhol
2022-05-11 20:56 ` Christophe JAILLET
2022-05-11 23:30 ` Vincent MAILHOL
2022-05-11 21:35 ` Nick Desaulniers
2022-05-11 23:48 ` Vincent MAILHOL
2022-05-11 16:03 ` [PATCH v2 2/2] x86/asm/bitops: __ffs,ffz: use __builtin_ctzl " Vincent Mailhol
2022-05-11 22:20 ` Nick Desaulniers
2022-05-11 23:23 ` Vincent MAILHOL
2022-05-12 0:03 ` [PATCH v3 0/2] x86/asm/bitops: optimize ff{s,z} functions for " Vincent Mailhol
2022-05-12 0:03 ` [PATCH v3 1/2] x86/asm/bitops: ffs: use __builtin_ffs to evaluate " Vincent Mailhol
2022-05-12 0:28 ` Nick Desaulniers
2022-05-12 1:18 ` Vincent MAILHOL
2022-05-12 0:03 ` [PATCH v3 2/2] x86/asm/bitops: __ffs,ffz: use __builtin_ctzl " Vincent Mailhol
2022-05-12 0:19 ` Nick Desaulniers
2022-05-12 1:18 ` [PATCH v4 0/2] x86/asm/bitops: optimize ff{s,z} functions for " Vincent Mailhol
2022-05-12 1:18 ` [PATCH v4 1/2] x86/asm/bitops: ffs: use __builtin_ffs to evaluate " Vincent Mailhol
2022-05-12 3:02 ` Joe Perches
2022-05-12 4:29 ` Vincent MAILHOL
2022-05-12 1:18 ` [PATCH v4 2/2] x86/asm/bitops: __ffs,ffz: use __builtin_ctzl " Vincent Mailhol
2022-05-23 9:22 ` [PATCH v4 0/2] x86/asm/bitops: optimize ff{s,z} functions for " Vincent MAILHOL
2022-06-25 7:26 ` [RESEND PATCH " Vincent Mailhol
2022-06-25 7:26 ` [RESEND PATCH v4 1/2] x86/asm/bitops: ffs: use __builtin_ffs to evaluate " Vincent Mailhol
2022-06-25 7:26 ` [RESEND PATCH v4 2/2] x86/asm/bitops: __ffs,ffz: use __builtin_ctzl " Vincent Mailhol
2022-07-23 15:15 ` [RESEND PATCH v4 0/2] x86/asm/bitops: optimize ff{s,z} functions for " Vincent Mailhol
2022-07-23 15:15 ` [RESEND PATCH v4 1/2] x86/asm/bitops: ffs: use __builtin_ffs to evaluate " Vincent Mailhol
2022-08-11 14:59 ` Borislav Petkov
2022-08-12 11:55 ` Vincent MAILHOL
2022-07-23 15:15 ` [RESEND PATCH v4 2/2] x86/asm/bitops: __ffs,ffz: use __builtin_ctzl " Vincent Mailhol
2022-07-29 11:24 ` [RESEND PATCH v4 0/2] x86/asm/bitops: optimize ff{s,z} functions for " Vincent MAILHOL
2022-07-29 12:22 ` Borislav Petkov
2022-07-29 13:50 ` Vincent MAILHOL
2022-08-12 11:44 ` [PATCH v5 " Vincent Mailhol
2022-08-12 11:44 ` [PATCH v5 1/2] x86/asm/bitops: ffs: use __builtin_ffs to evaluate " Vincent Mailhol
2022-08-12 11:44 ` [PATCH v5 2/2] x86/asm/bitops: __ffs,ffz: use __builtin_ctzl " Vincent Mailhol
2022-08-23 16:23 ` Borislav Petkov
2022-08-23 17:12 ` Nick Desaulniers
2022-08-23 17:43 ` Borislav Petkov
2022-08-23 20:31 ` Vincent MAILHOL
2022-08-24 8:43 ` Borislav Petkov
2022-08-24 12:10 ` Vincent MAILHOL
2022-08-24 13:24 ` Borislav Petkov
2022-08-26 21:32 ` Vincent MAILHOL
2022-09-07 4:06 ` Borislav Petkov [this message]
2022-09-07 5:35 ` Vincent MAILHOL
2022-09-07 8:50 ` Borislav Petkov
2022-08-31 7:57 ` [PATCH v6 0/2] x86/asm/bitops: optimize ff{s,z} functions for " Vincent Mailhol
2022-08-31 7:57 ` [PATCH v6 1/2] x86/asm/bitops: ffs: use __builtin_ffs to evaluate " Vincent Mailhol
2022-08-31 7:57 ` [PATCH v6 2/2] x86/asm/bitops: __ffs,ffz: use __builtin_ctzl " Vincent Mailhol
2022-08-31 8:51 ` [PATCH v6 0/2] x86/asm/bitops: optimize ff{s,z} functions for " Yury Norov
2022-09-01 3:49 ` Yury Norov
2022-09-01 10:30 ` Vincent MAILHOL
2022-09-01 14:19 ` Yury Norov
2022-09-01 17:06 ` Nick Desaulniers
2022-09-02 5:34 ` Borislav Petkov
2022-09-02 0:41 ` Vincent MAILHOL
2022-09-02 1:19 ` Vincent MAILHOL
2022-09-05 0:37 ` [PATCH v7 " Vincent Mailhol
2022-09-05 0:37 ` [PATCH v7 1/2] x86/asm/bitops: ffs: use __builtin_ffs to evaluate " Vincent Mailhol
2022-09-05 0:37 ` [PATCH v7 2/2] x86/asm/bitops: __ffs,ffz: use __builtin_ctzl " Vincent Mailhol
2022-09-06 18:26 ` [PATCH v7 0/2] x86/asm/bitops: optimize ff{s,z} functions for " Nick Desaulniers
2022-09-07 7:04 ` Nick Desaulniers
2022-09-07 7:49 ` Vincent MAILHOL
2022-09-07 9:09 ` [PATCH v8 " Vincent Mailhol
2022-09-07 9:09 ` [PATCH v8 1/2] x86/asm/bitops: ffs: use __builtin_ffs to evaluate " Vincent Mailhol
2022-09-07 9:09 ` [PATCH v8 2/2] x86/asm/bitops: __ffs,ffz: use __builtin_ctzl " Vincent Mailhol
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