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From: Arvind Sankar <nivedita@alum.mit.edu>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Arvind Sankar <nivedita@alum.mit.edu>,
	Andrew Morton <akpm@linux-foundation.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>
Subject: Re: [PATCH] lib/string.c: Disable tree-loop-distribute-patterns
Date: Tue, 18 Aug 2020 23:04:42 -0400	[thread overview]
Message-ID: <20200819030442.GA3396810@rani.riverdale.lan> (raw)
In-Reply-To: <CAHk-=wik-oXnUpfZ6Hw37uLykc-_P0Apyn2XuX-odh-3Nzop8w@mail.gmail.com>

On Tue, Aug 18, 2020 at 05:44:03PM -0700, Linus Torvalds wrote:
> On Tue, Aug 18, 2020 at 4:43 PM Arvind Sankar <nivedita@alum.mit.edu> wrote:
> >
> > This by itself is insufficient for gcc if the optimization was
> > explicitly enabled by CFLAGS, so also add a flag to explicitly disable
> > it.
> 
> Using -fno-tree-loop-distribute-patterns seems to really be a bit too
> incestuous with internal compiler knowledge.

Fair enough -- you ok with just the -ffreestanding? That's what protects
the memset in arch/x86/boot/compressed/string.c.

I think this is worthwhile to be safe.

> 
> That generic memcpy implementation is horrible anyway. It should never be used.
> 
> So I'd rather see this either removed entirely, ot possibly rewritten
> to be a somewhat proper memcpy implementation, and in the process made
> to not be recognizable by the compiler (possibly by adding a dummy
> barrier() or something like that).
> 
> Looking at the implementation of "strscpy()" in the same file, and
> then comparing that to the ludicrously simplisting "memcpy()", I
> really get the feeling that that memcpy() is not worth having.
> 
>               Linus

I don't think anything actually uses the generic memcpy, and I think
only c6x uses the generic memset. Might be worth optimizing strnlen etc
with the word-at-a-time thing though.

  reply	other threads:[~2020-08-19  3:04 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-18 23:43 [PATCH] lib/string.c: Disable tree-loop-distribute-patterns Arvind Sankar
2020-08-19  0:44 ` Linus Torvalds
2020-08-19  3:04   ` Arvind Sankar [this message]
2020-08-19  3:32     ` Linus Torvalds
2020-08-19 13:16       ` Arvind Sankar
2020-08-19 14:08       ` [PATCH v2] lib/string.c: Use freestanding environment Arvind Sankar
2020-08-19 18:35         ` Nick Desaulniers
2020-08-19 19:06           ` Arvind Sankar

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