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From: Kees Cook <keescook@chromium.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Randy Dunlap <rdunlap@infradead.org>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	Linux Next Mailing List <linux-next@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Nathan Chancellor <nathan@kernel.org>
Subject: Re: linux-next: Tree for Aug 20 (Wno-alloc-size-larger-than)
Date: Wed, 25 Aug 2021 10:04:19 -0700	[thread overview]
Message-ID: <202108250959.CD734CED@keescook> (raw)
In-Reply-To: <20210824115859.187f272f@canb.auug.org.au>

On Tue, Aug 24, 2021 at 11:58:59AM +1000, Stephen Rothwell wrote:
> On Mon, 23 Aug 2021 18:24:44 -0700 Randy Dunlap <rdunlap@infradead.org> wrote:
> >
> > This is just weird. What I am seeing is that for every source file
> > where gcc emits a warning: it then follows that up with this
> > >> cc1: warning: unrecognized command line option '-Wno-alloc-size-larger-than'  
> 
> I see the same, as well as:
> 
> <stdin>:1515:2: warning: #warning syscall clone3 not implemented [-Wcpp]
> cc1: warning: unrecognized command line option '-Wno-alloc-size-larger-than'
> 
> But only on my gcc 7.3.1 builds (the rest are gcc 10).
> 
> > Smells like a gcc bug to me.
> 
> Yes
> 
> Also noted here: https://github.com/DynamoRIO/drmemory/issues/2099 (second comment)

Okay, I think this work-around should work. I've been able to reproduce
the weird conditions, and this seems to behave correctly. Andrew, can
you fixup the fixup with this?


diff --git a/Makefile b/Makefile
index 26640899e7ca..c1842014a5de 100644
--- a/Makefile
+++ b/Makefile
@@ -1094,8 +1094,13 @@ endif
 
 ifdef CONFIG_CC_IS_GCC
 # The allocators already balk at large sizes, so silence the compiler
-# warnings for bounds checks involving those possible values.
-KBUILD_CFLAGS += $(call cc-option, -Wno-alloc-size-larger-than)
+# warnings for bounds checks involving those possible values. While
+# -Wno-alloc-size-larger-than would normally be used here, some versions
+# of gcc (<9.1) weirdly don't handle the option correctly when _other_
+# warnings are produced (?!), so instead use SIZE_MAX to effectively
+# disable it.
+# https://lore.kernel.org/lkml/20210824115859.187f272f@canb.auug.org.au
+KBUILD_CFLAGS += $(call cc-option, -Walloc-size-larger-than=SIZE_MAX)
 endif
 
 # disable invalid "can't wrap" optimizations for signed / pointers


-- 
Kees Cook

  parent reply	other threads:[~2021-08-25 17:04 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-20  9:26 linux-next: Tree for Aug 20 Stephen Rothwell
2021-08-20 21:54 ` linux-next: Tree for Aug 20 (Wno-alloc-size-larger-than) Randy Dunlap
2021-08-21  5:48   ` Kees Cook
2021-08-21 19:09     ` Randy Dunlap
2021-08-23 10:37       ` Stephen Rothwell
2021-08-24  1:24         ` Randy Dunlap
2021-08-24  1:58           ` Stephen Rothwell
2021-08-25  1:59             ` Kees Cook
2021-08-25 17:04             ` Kees Cook [this message]
2021-08-25 17:49               ` Randy Dunlap
2021-08-26  3:54                 ` Kees Cook
2021-08-26  5:10                   ` Randy Dunlap
2021-08-26  5:23                     ` Kees Cook

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