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Subject: |
shred.c i686-specific warning from gcc-4.7 on fedora 17 |
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Date: |
Thu, 12 Jul 2012 23:27:15 +0200 |
[mostly for the record, and so I don't forget.
I'm not ready to push this just yet. ]
Building shred with fedora 17 and its stock gcc 4.7 on i686,
I see this warning/error:
CC shred.o
shred.c: In function 'dopass':
shred.c:501:14: error: assuming signed overflow does not occur when
simplifying conditional to constant [-Werror=strict-overflow]
shred.c:504:18: error: assuming signed overflow does not occur when
simplifying conditional to constant [-Werror=strict-overflow]
cc1: all warnings being treated as errors
make[3]: *** [shred.o] Error 1
make[3]: Leaving directory `/f12/home/meyering/w/co/cu/src'
make[2]: *** [all] Error 2
make[2]: Leaving directory `/f12/home/meyering/w/co/cu/src'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/f12/home/meyering/w/co/cu'
make: *** [all] Error 2
I didn't really understand the cause but ended up
writing the following patch to avoid the problem
while making the code slightly more readable:
diff --git a/src/shred.c b/src/shred.c
index 7a28260..322bcf1 100644
--- a/src/shred.c
+++ b/src/shred.c
@@ -485,10 +485,11 @@ dopass (int fd, char const *qname, off_t *sizep, int type,
offset += soff;
+ bool done = offset == size;
+
/* Time to print progress? */
- if (n
- && ((offset == size && *previous_human_offset)
- || thresh <= (now = time (NULL))))
+ if (n && ((done && *previous_human_offset)
+ || thresh <= (now = time (NULL))))
{
char offset_buf[LONGEST_HUMAN_READABLE + 1];
char size_buf[LONGEST_HUMAN_READABLE + 1];
@@ -498,8 +499,7 @@ dopass (int fd, char const *qname, off_t *sizep, int type,
= human_readable (offset, offset_buf,
human_floor | human_progress_opts, 1, 1);
- if (offset == size
- || !STREQ (previous_human_offset, human_offset))
+ if (done || !STREQ (previous_human_offset, human_offset))
{
if (size < 0)
error (0, 0, _("%s: pass %lu/%lu (%s)...%s"),
@@ -516,7 +516,7 @@ dopass (int fd, char const *qname, off_t *sizep, int type,
= human_readable (size, size_buf,
human_ceiling | human_progress_opts,
1, 1);
- if (offset == size)
+ if (done)
human_offset = human_size;
error (0, 0, _("%s: pass %lu/%lu (%s)...%s/%s %d%%"),
qname, k, n, pass_string, human_offset, human_size,
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--- Begin Message ---
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Subject: |
Re: bug#11927: shred.c i686-specific warning from gcc-4.7 on fedora 17 |
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Date: |
Sun, 15 Jul 2012 11:36:16 +0200 |
Paul Eggert wrote:
> On 07/12/2012 02:27 PM, Jim Meyering wrote:
>> I didn't really understand the cause
>
> That one is one of my least favorite warnings
> because sometimes it warns about real bugs but
> often, as in your case, the warning is either
> bogus or so hard to figure out that it might as
> well be bogus. I see that you and I and others have
> been filing GCC bug reports in this area:
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51309
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48267
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52904
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34515
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52560
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49234
>
> In this particular case the shred.c rewrite seems harmless.
Thanks for the review.
I've just hit it again, so have pushed this:
>From b255b9a68a0dcec113a193daa602bdcbda2658db Mon Sep 17 00:00:00 2001
From: Jim Meyering <address@hidden>
Date: Sun, 15 Jul 2012 11:31:18 +0200
Subject: [PATCH] build: shred.c: avoid i686-specific gcc -Wstrict-overflow
warning
* src/shred.c: Avoid gcc -Wstrict-overflow warning.
Addresses http://bugs.gnu.org/11927
---
src/shred.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/src/shred.c b/src/shred.c
index 7a28260..322bcf1 100644
--- a/src/shred.c
+++ b/src/shred.c
@@ -485,10 +485,11 @@ dopass (int fd, char const *qname, off_t *sizep, int type,
offset += soff;
+ bool done = offset == size;
+
/* Time to print progress? */
- if (n
- && ((offset == size && *previous_human_offset)
- || thresh <= (now = time (NULL))))
+ if (n && ((done && *previous_human_offset)
+ || thresh <= (now = time (NULL))))
{
char offset_buf[LONGEST_HUMAN_READABLE + 1];
char size_buf[LONGEST_HUMAN_READABLE + 1];
@@ -498,8 +499,7 @@ dopass (int fd, char const *qname, off_t *sizep, int type,
= human_readable (offset, offset_buf,
human_floor | human_progress_opts, 1, 1);
- if (offset == size
- || !STREQ (previous_human_offset, human_offset))
+ if (done || !STREQ (previous_human_offset, human_offset))
{
if (size < 0)
error (0, 0, _("%s: pass %lu/%lu (%s)...%s"),
@@ -516,7 +516,7 @@ dopass (int fd, char const *qname, off_t *sizep, int type,
= human_readable (size, size_buf,
human_ceiling | human_progress_opts,
1, 1);
- if (offset == size)
+ if (done)
human_offset = human_size;
error (0, 0, _("%s: pass %lu/%lu (%s)...%s/%s %d%%"),
qname, k, n, pass_string, human_offset, human_size,
--
1.7.11.2.194.g7bdb748
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