From: Segher Boessenkool <segher@kernel.crashing.org>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Marco Elver <elver@google.com>,
Mark Rutland <mark.rutland@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Mark Brown <broonie@kernel.org>,
Paul Mackerras <paulus@samba.org>,
kasan-dev <kasan-dev@googlegroups.com>,
linux-toolchains@vger.kernel.org,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v1] powerpc: Include running function as first entry in save_stack_trace() and friends
Date: Thu, 4 Mar 2021 13:24:47 -0600 [thread overview]
Message-ID: <20210304192447.GT29191@gate.crashing.org> (raw)
In-Reply-To: <CAKwvOd=wBArMwvtDC8zV-QjQa5UuwWoxksQ8j+hUCZzbEAn+Fw@mail.gmail.com>
On Thu, Mar 04, 2021 at 09:54:44AM -0800, Nick Desaulniers wrote:
> On Thu, Mar 4, 2021 at 9:42 AM Marco Elver <elver@google.com> wrote:
> include/linux/compiler.h:246:
> prevent_tail_call_optimization
>
> commit a9a3ed1eff36 ("x86: Fix early boot crash on gcc-10, third try")
That is much heavier than needed (an mb()). You can just put an empty
inline asm after a call before a return, and that call cannot be
optimised to a sibling call: (the end of a function is an implicit
return:)
Instead of:
void g(void);
void f(int x)
if (x)
g();
}
Do:
void g(void);
void f(int x)
if (x)
g();
asm("");
}
This costs no extra instructions, and certainly not something as heavy
as an mb()! It works without the "if" as well, of course, but with it
it is a more interesting example of a tail call.
Segher
WARNING: multiple messages have this Message-ID (diff)
From: Segher Boessenkool <segher@kernel.crashing.org>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
Marco Elver <elver@google.com>,
Catalin Marinas <catalin.marinas@arm.com>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
LKML <linux-kernel@vger.kernel.org>,
kasan-dev <kasan-dev@googlegroups.com>,
Mark Brown <broonie@kernel.org>,
Paul Mackerras <paulus@samba.org>,
linux-toolchains@vger.kernel.org, Will Deacon <will@kernel.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v1] powerpc: Include running function as first entry in save_stack_trace() and friends
Date: Thu, 4 Mar 2021 13:24:47 -0600 [thread overview]
Message-ID: <20210304192447.GT29191@gate.crashing.org> (raw)
In-Reply-To: <CAKwvOd=wBArMwvtDC8zV-QjQa5UuwWoxksQ8j+hUCZzbEAn+Fw@mail.gmail.com>
On Thu, Mar 04, 2021 at 09:54:44AM -0800, Nick Desaulniers wrote:
> On Thu, Mar 4, 2021 at 9:42 AM Marco Elver <elver@google.com> wrote:
> include/linux/compiler.h:246:
> prevent_tail_call_optimization
>
> commit a9a3ed1eff36 ("x86: Fix early boot crash on gcc-10, third try")
That is much heavier than needed (an mb()). You can just put an empty
inline asm after a call before a return, and that call cannot be
optimised to a sibling call: (the end of a function is an implicit
return:)
Instead of:
void g(void);
void f(int x)
if (x)
g();
}
Do:
void g(void);
void f(int x)
if (x)
g();
asm("");
}
This costs no extra instructions, and certainly not something as heavy
as an mb()! It works without the "if" as well, of course, but with it
it is a more interesting example of a tail call.
Segher
WARNING: multiple messages have this Message-ID (diff)
From: Segher Boessenkool <segher@kernel.crashing.org>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Marco Elver <elver@google.com>,
Mark Rutland <mark.rutland@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Mark Brown <broonie@kernel.org>,
Paul Mackerras <paulus@samba.org>,
kasan-dev <kasan-dev@googlegroups.com>,
linux-toolchains@vger.kernel.org,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v1] powerpc: Include running function as first entry in save_stack_trace() and friends
Date: Thu, 4 Mar 2021 13:24:47 -0600 [thread overview]
Message-ID: <20210304192447.GT29191@gate.crashing.org> (raw)
In-Reply-To: <CAKwvOd=wBArMwvtDC8zV-QjQa5UuwWoxksQ8j+hUCZzbEAn+Fw@mail.gmail.com>
On Thu, Mar 04, 2021 at 09:54:44AM -0800, Nick Desaulniers wrote:
> On Thu, Mar 4, 2021 at 9:42 AM Marco Elver <elver@google.com> wrote:
> include/linux/compiler.h:246:
> prevent_tail_call_optimization
>
> commit a9a3ed1eff36 ("x86: Fix early boot crash on gcc-10, third try")
That is much heavier than needed (an mb()). You can just put an empty
inline asm after a call before a return, and that call cannot be
optimised to a sibling call: (the end of a function is an implicit
return:)
Instead of:
void g(void);
void f(int x)
if (x)
g();
}
Do:
void g(void);
void f(int x)
if (x)
g();
asm("");
}
This costs no extra instructions, and certainly not something as heavy
as an mb()! It works without the "if" as well, of course, but with it
it is a more interesting example of a tail call.
Segher
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-03-04 19:33 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-03 14:09 [PATCH v1] powerpc: Include running function as first entry in save_stack_trace() and friends Christophe Leroy
2021-03-03 14:09 ` Christophe Leroy
2021-03-03 14:38 ` Marco Elver
2021-03-03 14:38 ` Marco Elver
2021-03-03 14:52 ` Christophe Leroy
2021-03-03 14:52 ` Christophe Leroy
2021-03-03 15:20 ` Marco Elver
2021-03-03 15:20 ` Marco Elver
2021-03-03 15:20 ` Marco Elver
2021-03-04 14:57 ` Mark Rutland
2021-03-04 14:57 ` Mark Rutland
2021-03-04 14:57 ` Mark Rutland
2021-03-04 15:30 ` Marco Elver
2021-03-04 15:30 ` Marco Elver
2021-03-04 15:30 ` Marco Elver
2021-03-04 16:59 ` Mark Rutland
2021-03-04 16:59 ` Mark Rutland
2021-03-04 16:59 ` Mark Rutland
2021-03-04 17:25 ` Marco Elver
2021-03-04 17:25 ` Marco Elver
2021-03-04 17:25 ` Marco Elver
2021-03-04 17:54 ` Nick Desaulniers
2021-03-04 17:54 ` Nick Desaulniers
2021-03-04 17:54 ` Nick Desaulniers
2021-03-04 19:24 ` Segher Boessenkool [this message]
2021-03-04 19:24 ` Segher Boessenkool
2021-03-04 19:24 ` Segher Boessenkool
2021-03-05 6:38 ` Christophe Leroy
2021-03-05 6:38 ` Christophe Leroy
2021-03-05 6:38 ` Christophe Leroy
2021-03-05 18:16 ` Segher Boessenkool
2021-03-05 18:16 ` Segher Boessenkool
2021-03-05 18:16 ` Segher Boessenkool
2021-03-04 18:01 ` Mark Rutland
2021-03-04 18:01 ` Mark Rutland
2021-03-04 18:01 ` Mark Rutland
2021-03-04 18:22 ` Marco Elver
2021-03-04 18:22 ` Marco Elver
2021-03-04 18:22 ` Marco Elver
2021-03-04 18:51 ` Mark Rutland
2021-03-04 18:51 ` Mark Rutland
2021-03-04 18:51 ` Mark Rutland
2021-03-04 19:01 ` Marco Elver
2021-03-04 19:01 ` Marco Elver
2021-03-04 19:01 ` Marco Elver
2021-03-05 12:04 ` Mark Rutland
2021-03-05 12:04 ` Mark Rutland
2021-03-05 12:04 ` Mark Rutland
2021-03-04 21:54 ` Segher Boessenkool
2021-03-04 21:54 ` Segher Boessenkool
2021-03-04 21:54 ` Segher Boessenkool
2021-03-09 16:05 ` Mark Rutland
2021-03-09 16:05 ` Mark Rutland
2021-03-09 16:05 ` Mark Rutland
2021-03-09 22:05 ` Segher Boessenkool
2021-03-09 22:05 ` Segher Boessenkool
2021-03-09 22:05 ` Segher Boessenkool
2021-03-10 11:32 ` Mark Rutland
2021-03-10 11:32 ` Mark Rutland
2021-03-10 11:32 ` Mark Rutland
2021-03-10 17:37 ` Segher Boessenkool
2021-03-10 17:37 ` Segher Boessenkool
2021-03-10 17:37 ` Segher Boessenkool
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