linux-kernel - Re: [announce] new tree: "fix all build warnings, on all configs"

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Date:	Sat, 18 Oct 2008 10:22:09 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Roland Dreier <rdreier@...co.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"David S. Miller" <davem@...emloft.net>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	David Howells <dhowells@...hat.com>
Subject: Re: [announce] new tree: "fix all build warnings, on all configs"


* Roland Dreier <rdreier@...co.com> wrote:

>  > i certainly have a found a couple of such cases, see tip/warnings/ugly - 
>  > for example see the one below where gcc is not able to see through type 
>  > width.
> 
> Yes, the uninitialized variable warnings are obnoxious too.  By the way,
> I think this:
> 
> @@ -72,7 +72,7 @@ static __always_inline void *__constant_memcpy(void *to, const void *from,
>  		return to;
>  	case 5:
>  		*(int *)to = *(int *)from;
> -		*((char *)to + 4) = *((char *)from + 4);
> +		*((short *)to + 3) = *((short *)from + 3);
>  		return to;
>  	case 6:
>  		*(int *)to = *(int *)from;
> 
> is actually *wrong*, because the cast operator binds tighter than
> addition -- so
> 
> +		*((short *)to + 3) = *((short *)from + 3);
> 
> actually copies bytes at offset 6 and 7; I think what you intended was:
> 
> +		*((short *)(to + 3)) = *((short *)(from + 3));

thx, you are right - fixed it via the patch below.

> which illustrates the risks in fixing warnings.

yeah. Note that this was not a routine case at all, i did the commit in 
the early stages when i didnt even know how much effort it all would be 
to keep the whole kernel warning-free, in all configs. It looked odd and 
ugly and was in tip/warnings/ugly rightfully.

It would be nice if you could find an outright incorrect change in 
tip/warnings/simple. The ones flagged 'simple' are the ones that have 
the highest risk of not being reviewed much beyond their initial 
addition.

	Ingo

--------------->
>From 9d8f9578ca252bf26474ed77fde7ea30e9dee595 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@...e.hu>
Date: Sat, 18 Oct 2008 10:17:36 +0200
Subject: [PATCH] hack, workaround for warning drivers/acpi/tables/tbfadt.c, fix

Fix commit fbf03326a16b29f8d34a5a3883a267bac4d38fc2, pointed
out by Roland Dreier.

Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 include/asm-x86/string_32.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/include/asm-x86/string_32.h b/include/asm-x86/string_32.h
index 419ab10..be82619 100644
--- a/include/asm-x86/string_32.h
+++ b/include/asm-x86/string_32.h
@@ -72,7 +72,7 @@ static __always_inline void *__constant_memcpy(void *to, const void *from,
 		return to;
 	case 5:
 		*(int *)to = *(int *)from;
-		*((short *)to + 3) = *((short *)from + 3);
+		*((char *)(to + 3)) = *((char *)(from + 3));
 		return to;
 	case 6:
 		*(int *)to = *(int *)from;
--
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