NetBSD Problem Report #36668
From martin@duskware.de Fri Jul 20 09:02:02 2007
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Date: Fri, 20 Jul 2007 08:59:03 +0000 (UTC)
From: mccratch@gmx.net
Reply-To: mccratch@gmx.net
To: netbsd-bugs-owner@NetBSD.org
Subject: bogus complaints about sys/endian.h code when running lint -aa
X-Send-Pr-Version: www-1.0
>Number: 36668
>Category: lib
>Synopsis: bogus complaints about sys/endian.h code when running lint -aa
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: rillig
>State: closed
>Class: change-request
>Submitter-Id: net
>Arrival-Date: Fri Jul 20 09:05:00 +0000 2007
>Closed-Date: Thu May 26 09:37:40 +0000 2022
>Last-Modified: Thu May 26 20:20:02 +0000 2022
>Originator: Matthias Kretschmer
>Release: 4.0_BETA2
>Organization:
>Environment:
NetBSD tiger 4.0_BETA2 NetBSD 4.0_BETA2 (GENERIC.MP) #4: Tue Jun 5 15:52:40 CEST 2007
>Description:
"lint -aa" complains about "may loose accuracy" for sys/endian.h.
This is no bug at all, just annoying when using lint -aa.
>How-To-Repeat:
$ cat > test.c << EOF
#include <sys/endian.h>
EOF
$ lint -aa test.c
>Fix:
Add explicit typecasts (e.g. applying the following patch to sys/endian.h).
The semantics of the code aren't touched as the compiler has to implicitly cast the values to the given types when running this code.
--- endian.h.orig 2005-02-03 20:16:10.000000000 +0100
+++ endian.h 2007-07-20 10:23:33.000000000 +0200
@@ -190,8 +190,8 @@
{
uint8_t *p = (uint8_t *)buf;
- p[0] = ((unsigned)u >> 8) & 0xff;
- p[1] = u & 0xff;
+ p[0] = (uint8_t)(((unsigned)u >> 8) & 0xff);
+ p[1] = (uint8_t)(u & 0xff);
}
static __inline void __unused
@@ -199,8 +199,8 @@
{
uint8_t *p = (uint8_t *)buf;
- p[0] = u & 0xff;
- p[1] = ((unsigned)u >> 8) & 0xff;
+ p[0] = (uint8_t)(u & 0xff);
+ p[1] = (uint8_t)(((unsigned)u >> 8) & 0xff);
}
static __inline uint16_t __unused
@@ -208,7 +208,7 @@
{
const uint8_t *p = (const uint8_t *)buf;
- return ((p[0] << 8) | p[1]);
+ return (uint16_t)((p[0] << 8) | p[1]);
}
static __inline uint16_t __unused
@@ -216,7 +216,7 @@
{
const uint8_t *p = (const uint8_t *)buf;
- return ((p[1] << 8) | p[0]);
+ return (uint16_t)((p[1] << 8) | p[0]);
}
static __inline void __unused
@@ -224,10 +224,10 @@
{
uint8_t *p = (uint8_t *)buf;
- p[0] = (u >> 24) & 0xff;
- p[1] = (u >> 16) & 0xff;
- p[2] = (u >> 8) & 0xff;
- p[3] = u & 0xff;
+ p[0] = (uint8_t)((u >> 24) & 0xff);
+ p[1] = (uint8_t)((u >> 16) & 0xff);
+ p[2] = (uint8_t)((u >> 8) & 0xff);
+ p[3] = (uint8_t)(u & 0xff);
}
static __inline void __unused
@@ -235,10 +235,10 @@
{
uint8_t *p = (uint8_t *)buf;
- p[0] = u & 0xff;
- p[1] = (u >> 8) & 0xff;
- p[2] = (u >> 16) & 0xff;
- p[3] = (u >> 24) & 0xff;
+ p[0] = (uint8_t)(u & 0xff);
+ p[1] = (uint8_t)((u >> 8) & 0xff);
+ p[2] = (uint8_t)((u >> 16) & 0xff);
+ p[3] = (uint8_t)((u >> 24) & 0xff);
}
static __inline uint32_t __unused
>Release-Note:
>Audit-Trail:
From: Christos Zoulas <christos@netbsd.org>
To: gnats-bugs@NetBSD.org
Cc:
Subject: PR/36668 CVS commit: src/sys/sys
Date: Fri, 20 Jul 2007 15:07:15 +0000 (UTC)
Module Name: src
Committed By: christos
Date: Fri Jul 20 15:07:15 UTC 2007
Modified Files:
src/sys/sys: endian.h
Log Message:
PR/36668: Matthias Kretschmer: Silence lint -aa complaints about "may lose
accuracy".
To generate a diff of this commit:
cvs rdiff -r1.25 -r1.26 src/sys/sys/endian.h
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
From: David Laight <david@l8s.co.uk>
To: gnats-bugs@NetBSD.org
Cc:
Subject: Re: lib/36668: bogus complaints about sys/endian.h code when running lint -aa
Date: Fri, 20 Jul 2007 16:50:26 +0100
On Fri, Jul 20, 2007 at 09:05:00AM +0000, mccratch@gmx.net wrote:
> >Number: 36668
> >Category: lib
> >Synopsis: bogus complaints about sys/endian.h code when running lint -aa
> "lint -aa" complains about "may loose accuracy" for sys/endian.h.
> This is no bug at all, just annoying when using lint -aa.
> - p[1] = u & 0xff;
> + p[1] = (uint8_t)(u & 0xff);
There is a big problem with adding such casts, they can very easily
hide other (bigger) problems with the source.
Especially if applied to every place an implicit integer narrowing
conversion happens.
David
--
David Laight: david@l8s.co.uk
From: Matthias Kretschmer <mccratch@gmx.de>
To: gnats-bugs@NetBSD.org
Cc:
Subject: Re: lib/36668: bogus complaints about sys/endian.h code when running lint -aa
Date: Fri, 20 Jul 2007 22:50:31 +0200
On Fri, Jul 20, 2007 at 03:55:02PM +0000, David Laight wrote:
> From: David Laight <david@l8s.co.uk>
> > - p[1] = u & 0xff;
> > + p[1] = (uint8_t)(u & 0xff);
>
> There is a big problem with adding such casts, they can very easily
> hide other (bigger) problems with the source.
> Especially if applied to every place an implicit integer narrowing
> conversion happens.
The meaning of the code doesn't change and I don't see where there are
any problems with this code as it just does the right thing. It's
nothing more than that lint is unable to tell that "u & 0xff" will
really be just 8-bits long. Similiar for other parts of the code in
endian.h.
--
Matthias Kretschmer
Responsible-Changed-From-To: lib-bug-people->rillig
Responsible-Changed-By: rillig@NetBSD.org
Responsible-Changed-When: Wed, 25 May 2022 23:31:24 +0000
Responsible-Changed-Why:
I'm taking it, my plan is to fix the wrong lint warning.
From: "Roland Illig" <rillig@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc:
Subject: PR/36668 CVS commit: src/tests/usr.bin/xlint/lint1
Date: Thu, 26 May 2022 07:03:03 +0000
Module Name: src
Committed By: rillig
Date: Thu May 26 07:03:03 UTC 2022
Modified Files:
src/tests/usr.bin/xlint/lint1: msg_132.c msg_132.exp
Log Message:
tests/lint: demonstrate wrong 'may lose accuracy' warning
Reported in PR 36668, fixed in sys/sys/endian.h 1.26 from 2007-07-20,
unfixed in sys/sys/endian.h 1.29 from 2014-03-18.
To generate a diff of this commit:
cvs rdiff -u -r1.9 -r1.10 src/tests/usr.bin/xlint/lint1/msg_132.c
cvs rdiff -u -r1.8 -r1.9 src/tests/usr.bin/xlint/lint1/msg_132.exp
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
From: "Roland Illig" <rillig@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc:
Subject: PR/36668 CVS commit: src
Date: Thu, 26 May 2022 09:26:00 +0000
Module Name: src
Committed By: rillig
Date: Thu May 26 09:26:00 UTC 2022
Modified Files:
src/tests/usr.bin/xlint/lint1: msg_132.c msg_132.exp
src/usr.bin/xlint/lint1: tree.c
Log Message:
lint: do not warn about loss in accuracy if the actual value fits
The expression 'any & 0xff' can always be assigned to 'uint8_t' without
loss of any value bits. In the same way, '(any & 0xff) << 8' can always
be assigned to 'uint16_t'.
Previously, lint warned about these cases. Fix these wrong warnings by
tracking the possible values of integer expressions across a single
expression.
Fixes PR 36668, so that <sys/endian.h> does not need to be cluttered
with useless casts anymore.
To generate a diff of this commit:
cvs rdiff -u -r1.10 -r1.11 src/tests/usr.bin/xlint/lint1/msg_132.c
cvs rdiff -u -r1.9 -r1.10 src/tests/usr.bin/xlint/lint1/msg_132.exp
cvs rdiff -u -r1.443 -r1.444 src/usr.bin/xlint/lint1/tree.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
State-Changed-From-To: open->closed
State-Changed-By: rillig@NetBSD.org
State-Changed-When: Thu, 26 May 2022 09:37:40 +0000
State-Changed-Why:
Fixed for NetBSD 10, thanks for the PR.
From: "Roland Illig" <rillig@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc:
Subject: PR/36668 CVS commit: src
Date: Thu, 26 May 2022 20:17:40 +0000
Module Name: src
Committed By: rillig
Date: Thu May 26 20:17:40 UTC 2022
Modified Files:
src/tests/usr.bin/xlint/lint1: msg_132.c msg_132.exp
src/usr.bin/xlint/lint1: tree.c
Log Message:
lint: do not warn about 'uint32_t = uint64_t >> 32'
If all possible values fit into the destination type, there is no
possibility of losing accuracy.
Enhances PR 36668.
To generate a diff of this commit:
cvs rdiff -u -r1.12 -r1.13 src/tests/usr.bin/xlint/lint1/msg_132.c
cvs rdiff -u -r1.11 -r1.12 src/tests/usr.bin/xlint/lint1/msg_132.exp
cvs rdiff -u -r1.448 -r1.449 src/usr.bin/xlint/lint1/tree.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
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