From: Segher Boessenkool <segher@kernel.crashing.org>
To: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
nathanl@linux.ibm.com, anton@ozlabs.org,
linux-arch@vger.kernel.org, arnd@arndb.de,
linux-kernel@vger.kernel.org, luto@kernel.org,
tglx@linutronix.de, vincenzo.frascino@arm.com,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v10 2/5] powerpc/vdso: Prepare for switching VDSO to generic C implementation.
Date: Wed, 5 Aug 2020 15:55:56 -0500 [thread overview]
Message-ID: <20200805205556.GR6753@gate.crashing.org> (raw)
In-Reply-To: <7d409421-6396-8eba-8250-b6c9ff8232d9@csgroup.eu>
Hi!
On Wed, Aug 05, 2020 at 06:51:44PM +0200, Christophe Leroy wrote:
> Le 05/08/2020 à 16:03, Segher Boessenkool a écrit :
> >On Wed, Aug 05, 2020 at 07:09:23AM +0000, Christophe Leroy wrote:
> >>+/*
> >>+ * The macros sets two stack frames, one for the caller and one for the
> >>callee
> >>+ * because there are no requirement for the caller to set a stack frame
> >>when
> >>+ * calling VDSO so it may have omitted to set one, especially on PPC64
> >>+ */
> >
> >If the caller follows the ABI, there always is a stack frame. So what
> >is going on?
>
> Looks like it is not the case. See discussion at
> https://patchwork.ozlabs.org/project/linuxppc-dev/patch/2a67c333893454868bbfda773ba4b01c20272a5d.1588079622.git.christophe.leroy@c-s.fr/
>
> Seems like GCC uses the redzone and doesn't set a stack frame. I guess
> it doesn't know that the inline assembly contains a function call so it
> doesn't set the frame.
Yes, that is the problem. See
https://gcc.gnu.org/onlinedocs/gcc-10.2.0/gcc/Extended-Asm.html#AssemblerTemplate
where this is (briefly) discussed:
"Accessing data from C programs without using input/output operands
(such as by using global symbols directly from the assembler
template) may not work as expected. Similarly, calling functions
directly from an assembler template requires a detailed understanding
of the target assembler and ABI."
I don't know of a good way to tell GCC some function needs a frame (that
is, one that doesn't result in extra code other than to set up the
frame). I'll think about it.
Segher
next prev parent reply other threads:[~2020-08-05 20:56 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-05 7:09 [PATCH v10 0/5] powerpc: switch VDSO to C implementation Christophe Leroy
2020-08-05 7:09 ` [PATCH v10 1/5] powerpc/processor: Move cpu_relax() into asm/vdso/processor.h Christophe Leroy
2020-08-05 7:09 ` [PATCH v10 2/5] powerpc/vdso: Prepare for switching VDSO to generic C implementation Christophe Leroy
2020-08-05 14:03 ` Segher Boessenkool
2020-08-05 14:03 ` Segher Boessenkool
2020-08-05 16:40 ` Christophe Leroy
2020-08-05 16:40 ` Christophe Leroy
2020-08-05 18:40 ` Segher Boessenkool
2020-08-05 18:40 ` Segher Boessenkool
2020-08-06 5:46 ` Christophe Leroy
2020-08-05 16:51 ` Christophe Leroy
2020-08-05 16:51 ` Christophe Leroy
2020-08-05 20:55 ` Segher Boessenkool [this message]
2020-08-05 7:09 ` [PATCH v10 3/5] powerpc/vdso: Save and restore TOC pointer on PPC64 Christophe Leroy
2020-08-05 7:09 ` [PATCH v10 4/5] powerpc/vdso: Switch VDSO to generic C implementation Christophe Leroy
2020-08-05 7:09 ` Christophe Leroy
2020-08-05 7:09 ` [PATCH v10 5/5] powerpc/vdso: Provide __kernel_clock_gettime64() on vdso32 Christophe Leroy
2020-08-05 7:09 ` Christophe Leroy
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