From: Segher Boessenkool <segher@kernel.crashing.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Sudip Mukherjee <sudipm.mukherjee@gmail.com>,
Kees Cook <keescook@chromium.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Paul Mackerras <paulus@samba.org>,
linux-hardening@vger.kernel.org,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Subject: Re: mainline build failure of powerpc allmodconfig for prom_init_check
Date: Sun, 17 Jul 2022 14:54:48 -0500 [thread overview]
Message-ID: <20220717195448.GB25951@gate.crashing.org> (raw)
In-Reply-To: <CAHk-=whc3Uvhrmrr27xp5=oOhSDjXc5s1ZxC3B7xMYV6oj4WRQ@mail.gmail.com>
On Sun, Jul 17, 2022 at 07:44:22AM -0700, Linus Torvalds wrote:
> On Sun, Jul 17, 2022 at 2:13 AM Sudip Mukherjee
> <sudipm.mukherjee@gmail.com> wrote:
> > I was trying to check it. With gcc-11 the assembly code generated is
> > not using memset, but using __memset.
> > But with gcc-12, I can see the assembly code is using memset. One
> > example from the assembly:
>
> You could try making the 'args' array in 'struct prom_args' be marked
> 'volatile'.
>
> Ie something like this:
>
> --- a/arch/powerpc/kernel/prom_init.c
> +++ b/arch/powerpc/kernel/prom_init.c
> @@ -115,6 +115,6 @@ struct prom_args {
> __be32 service;
> __be32 nargs;
> __be32 nret;
> - __be32 args[10];
> + volatile __be32 args[10];
> };
>
> because I think it's just the compilers turning the small loop over
> those fields into a "memset()".
Yes. See <https://gcc.gnu.org/onlinedocs/gcc/Standards.html#C-Language>
near the end:
Most of the compiler support routines used by GCC are present in
libgcc, but there are a few exceptions. GCC requires the freestanding
environment provide memcpy, memmove, memset and memcmp. Finally, if
__builtin_trap is used, and the target does not implement the trap
pattern, then GCC emits a call to abort.
Can't we simply have a small simple implementation of these functions in
arch/powerpc/boot/? This stuff is not performance-critical, and this is
not the first time we hit these problems.
Segher
next prev parent reply other threads:[~2022-07-17 20:01 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-14 8:55 mainline build failure of powerpc allmodconfig for prom_init_check Sudip Mukherjee (Codethink)
2022-07-17 9:12 ` Sudip Mukherjee
2022-07-17 14:44 ` Linus Torvalds
2022-07-17 19:54 ` Segher Boessenkool [this message]
2022-07-18 3:52 ` Michael Ellerman
2022-07-18 14:56 ` Segher Boessenkool
2022-07-17 20:25 ` Sudip Mukherjee
2022-07-17 20:29 ` Linus Torvalds
2022-07-17 20:38 ` Sudip Mukherjee
2022-07-17 20:56 ` Linus Torvalds
2022-07-17 20:56 ` Segher Boessenkool
2022-07-17 21:11 ` Linus Torvalds
2022-07-17 21:45 ` Segher Boessenkool
2022-07-18 1:38 ` Linus Torvalds
2022-07-18 4:41 ` Michael Ellerman
2022-07-18 7:51 ` David Laight
2022-07-18 13:44 ` [PATCH] powerpc/64s: Disable stack variable initialisation for prom_init Michael Ellerman
2022-07-18 15:03 ` Sudip Mukherjee
2022-07-18 18:34 ` Linus Torvalds
2022-07-18 19:06 ` mainline build failure of powerpc allmodconfig for prom_init_check Linus Torvalds
2022-07-18 22:08 ` Segher Boessenkool
2022-07-18 22:55 ` Linus Torvalds
2022-07-19 13:35 ` Michael Ellerman
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