* [musl] [PATCH] Fix signed compare warning
@ 2020-06-24 23:20 Daniel Santos
2020-06-25 15:58 ` Khem Raj
0 siblings, 1 reply; 6+ messages in thread
From: Daniel Santos @ 2020-06-24 23:20 UTC (permalink / raw)
To: musl; +Cc: daniel, Daniel Santos
Signed-off-by: Daniel Santos <daniel.santos@pobox.com>
---
src/thread/__timedwait.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/thread/__timedwait.c b/src/thread/__timedwait.c
index 666093be..9829b93e 100644
--- a/src/thread/__timedwait.c
+++ b/src/thread/__timedwait.c
@@ -38,7 +38,7 @@ int __timedwait_cp(volatile int *addr, int val,
if (priv) priv = FUTEX_PRIVATE;
if (at) {
- if (at->tv_nsec >= 1000000000UL) return EINVAL;
+ if ((unsigned long)at->tv_nsec >= 1000000000UL) return EINVAL;
if (__clock_gettime(clk, &to)) return EINVAL;
to.tv_sec = at->tv_sec - to.tv_sec;
if ((to.tv_nsec = at->tv_nsec - to.tv_nsec) < 0) {
--
2.24.1
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [musl] [PATCH] Fix signed compare warning
2020-06-24 23:20 [musl] [PATCH] Fix signed compare warning Daniel Santos
@ 2020-06-25 15:58 ` Khem Raj
2020-06-25 17:33 ` Rich Felker
2020-06-26 4:31 ` Daniel Santos
0 siblings, 2 replies; 6+ messages in thread
From: Khem Raj @ 2020-06-25 15:58 UTC (permalink / raw)
To: musl, Daniel Santos; +Cc: daniel
On 6/24/20 4:20 PM, Daniel Santos wrote:
> Signed-off-by: Daniel Santos <daniel.santos@pobox.com>
> ---
> src/thread/__timedwait.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/src/thread/__timedwait.c b/src/thread/__timedwait.c
> index 666093be..9829b93e 100644
> --- a/src/thread/__timedwait.c
> +++ b/src/thread/__timedwait.c
> @@ -38,7 +38,7 @@ int __timedwait_cp(volatile int *addr, int val,
> if (priv) priv = FUTEX_PRIVATE;
>
> if (at) {
> - if (at->tv_nsec >= 1000000000UL) return EINVAL;
> + if ((unsigned long)at->tv_nsec >= 1000000000UL) return EINVAL;
> if (__clock_gettime(clk, &to)) return EINVAL;
> to.tv_sec = at->tv_sec - to.tv_sec;
> if ((to.tv_nsec = at->tv_nsec - to.tv_nsec) < 0) {
>
may be use < 0 || >= 1000000000L and avoid the cast.
there is a similar issue in src/thread/pthread_cond_timedwait.c as well
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [musl] [PATCH] Fix signed compare warning
2020-06-25 15:58 ` Khem Raj
@ 2020-06-25 17:33 ` Rich Felker
2020-06-26 4:31 ` Daniel Santos
1 sibling, 0 replies; 6+ messages in thread
From: Rich Felker @ 2020-06-25 17:33 UTC (permalink / raw)
To: musl
On Thu, Jun 25, 2020 at 08:58:41AM -0700, Khem Raj wrote:
>
>
> On 6/24/20 4:20 PM, Daniel Santos wrote:
> > Signed-off-by: Daniel Santos <daniel.santos@pobox.com>
> > ---
> > src/thread/__timedwait.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/src/thread/__timedwait.c b/src/thread/__timedwait.c
> > index 666093be..9829b93e 100644
> > --- a/src/thread/__timedwait.c
> > +++ b/src/thread/__timedwait.c
> > @@ -38,7 +38,7 @@ int __timedwait_cp(volatile int *addr, int val,
> > if (priv) priv = FUTEX_PRIVATE;
> >
> > if (at) {
> > - if (at->tv_nsec >= 1000000000UL) return EINVAL;
> > + if ((unsigned long)at->tv_nsec >= 1000000000UL) return EINVAL;
> > if (__clock_gettime(clk, &to)) return EINVAL;
> > to.tv_sec = at->tv_sec - to.tv_sec;
> > if ((to.tv_nsec = at->tv_nsec - to.tv_nsec) < 0) {
> >
> may be use < 0 || >= 1000000000L and avoid the cast.
> there is a similar issue in src/thread/pthread_cond_timedwait.c as well
This is not a bug but intentional usage of the language.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [musl] [PATCH] Fix signed compare warning
2020-06-25 15:58 ` Khem Raj
2020-06-25 17:33 ` Rich Felker
@ 2020-06-26 4:31 ` Daniel Santos
2020-06-26 6:26 ` Jeffrey Walton
1 sibling, 1 reply; 6+ messages in thread
From: Daniel Santos @ 2020-06-26 4:31 UTC (permalink / raw)
To: Khem Raj, musl, Daniel Santos
On 6/25/20 10:58 AM, Khem Raj wrote:
>
> On 6/24/20 4:20 PM, Daniel Santos wrote:
>> Signed-off-by: Daniel Santos <daniel.santos@pobox.com>
>> ---
>> src/thread/__timedwait.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/src/thread/__timedwait.c b/src/thread/__timedwait.c
>> index 666093be..9829b93e 100644
>> --- a/src/thread/__timedwait.c
>> +++ b/src/thread/__timedwait.c
>> @@ -38,7 +38,7 @@ int __timedwait_cp(volatile int *addr, int val,
>> if (priv) priv = FUTEX_PRIVATE;
>>
>> if (at) {
>> - if (at->tv_nsec >= 1000000000UL) return EINVAL;
>> + if ((unsigned long)at->tv_nsec >= 1000000000UL) return EINVAL;
>> if (__clock_gettime(clk, &to)) return EINVAL;
>> to.tv_sec = at->tv_sec - to.tv_sec;
>> if ((to.tv_nsec = at->tv_nsec - to.tv_nsec) < 0) {
>>
> may be use < 0 || >= 1000000000L and avoid the cast.
> there is a similar issue in src/thread/pthread_cond_timedwait.c as well
Thank you for that. I'll resubmit changing both instances.
In this case, the POSIX spec requires nt_nsec to be a long (
https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/time.h.html
). Either way, a good optimizer should convert this into an unsigned
compare. My early years in 6502 assembly sort-of shapes my thinking, as
I try to write higher level code as similarly to the assembly I presume
the compiler will emit. But if the project has a strong preference to
avoid casts, I can change it.
Thanks!
Daniel
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [musl] [PATCH] Fix signed compare warning
2020-06-26 4:31 ` Daniel Santos
@ 2020-06-26 6:26 ` Jeffrey Walton
2020-07-04 21:13 ` Daniel Santos
0 siblings, 1 reply; 6+ messages in thread
From: Jeffrey Walton @ 2020-06-26 6:26 UTC (permalink / raw)
To: musl; +Cc: Khem Raj, Daniel Santos
On Fri, Jun 26, 2020 at 2:20 AM Daniel Santos <daniel@gsat.us> wrote:
>
> ...
> >> if (at) {
> >> - if (at->tv_nsec >= 1000000000UL) return EINVAL;
> >> + if ((unsigned long)at->tv_nsec >= 1000000000UL) return EINVAL;
> >> if (__clock_gettime(clk, &to)) return EINVAL;
> >> to.tv_sec = at->tv_sec - to.tv_sec;
> >> if ((to.tv_nsec = at->tv_nsec - to.tv_nsec) < 0) {
> >>
> > may be use < 0 || >= 1000000000L and avoid the cast.
> > there is a similar issue in src/thread/pthread_cond_timedwait.c as well
> Thank you for that. I'll resubmit changing both instances.
>
> In this case, the POSIX spec requires nt_nsec to be a long (
> https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/time.h.html
> ). Either way, a good optimizer should convert this into an unsigned
I believe the C language says the signed value gets promoted to an
unsigned value. I don't believe the optimizer has anything to do with
it.
That's why -1 is greater than 1 in C:
int x = -1;
unsigned int y = 1;
if (x > y)
printf("WTF???\n");
Jeff
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [musl] [PATCH] Fix signed compare warning
2020-06-26 6:26 ` Jeffrey Walton
@ 2020-07-04 21:13 ` Daniel Santos
0 siblings, 0 replies; 6+ messages in thread
From: Daniel Santos @ 2020-07-04 21:13 UTC (permalink / raw)
To: musl
On 6/26/20 1:26 AM, Jeffrey Walton wrote:
> On Fri, Jun 26, 2020 at 2:20 AM Daniel Santos <daniel@gsat.us> wrote:
>> ...
>>>> if (at) {
>>>> - if (at->tv_nsec >= 1000000000UL) return EINVAL;
>>>> + if ((unsigned long)at->tv_nsec >= 1000000000UL) return EINVAL;
>>>> if (__clock_gettime(clk, &to)) return EINVAL;
>>>> to.tv_sec = at->tv_sec - to.tv_sec;
>>>> if ((to.tv_nsec = at->tv_nsec - to.tv_nsec) < 0) {
>>>>
>>> may be use < 0 || >= 1000000000L and avoid the cast.
>>> there is a similar issue in src/thread/pthread_cond_timedwait.c as well
>> Thank you for that. I'll resubmit changing both instances.
>>
>> In this case, the POSIX spec requires nt_nsec to be a long (
>> https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/time.h.html
>> ). Either way, a good optimizer should convert this into an unsigned
> I believe the C language says the signed value gets promoted to an
> unsigned value. I don't believe the optimizer has anything to do with
> it.
>
> That's why -1 is greater than 1 in C:
>
> int x = -1;
> unsigned int y = 1;
> if (x > y)
> printf("WTF???\n");
>
> Jeff
Yes, I was referring to Khem's suggestion:
may be use < 0 || >= 1000000000L and avoid the cast.
The optimizer should convert this into a single unsigned compare on just
about any modern processor (e.g., two's compliment).
I suppose the real solution is to not add -Wextra to CFLAGS unless you
add -Wno-sign-compare, as musl intentionally uses this promotion rule.
Thanks!
Daniel
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2020-07-04 21:16 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2020-06-24 23:20 [musl] [PATCH] Fix signed compare warning Daniel Santos
2020-06-25 15:58 ` Khem Raj
2020-06-25 17:33 ` Rich Felker
2020-06-26 4:31 ` Daniel Santos
2020-06-26 6:26 ` Jeffrey Walton
2020-07-04 21:13 ` Daniel Santos
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