[v2] linux: Avoid shifting a negative signed on POSIX timer interface
Commit Message
The current macros uses pid as signed value, which triggers a compiler
warning for process and thread timers. Replace MAKE_PROCESS_CPUCLOCK
with static inline function that expects the pid as unsigned. These
are similar to what Linux does internally.
Checked on x86_64-linux-gnu.
---
nptl/pthread_getcpuclockid.c | 2 +-
sysdeps/unix/sysv/linux/clock_getcpuclockid.c | 2 +-
sysdeps/unix/sysv/linux/clock_nanosleep.c | 2 +-
.../unix/sysv/linux/kernel-posix-cpu-timers.h | 28 +++++++++++++++----
sysdeps/unix/sysv/linux/timer_create.c | 4 +--
5 files changed, 28 insertions(+), 10 deletions(-)
Comments
Hi Adhemerval,
> The current macros uses pid as signed value, which triggers a compiler
> warning for process and thread timers. Replace MAKE_PROCESS_CPUCLOCK
> with static inline function that expects the pid as unsigned. These
> are similar to what Linux does internally.
>
> Checked on x86_64-linux-gnu.
I tried building master with -Wshift-negative-value and ran into a
couple of other left-shifts on negative values in
sysdeps/x86/dl-cacheinfo.h:
> count_mask = ~(-1 << (count_mask + 1));
Perhaps a cast of the -1 to unsigned here would make the intent even
more clear, and get glibc building cleanly with
-Wshift-negative-value. What do you think?
Anyway, this patch itself looks good to me.
Reviewed-by: Arjun Shankar <arjun@redhat.com>
> nptl/pthread_getcpuclockid.c | 2 +-
> sysdeps/unix/sysv/linux/clock_getcpuclockid.c | 2 +-
> sysdeps/unix/sysv/linux/clock_nanosleep.c | 2 +-
> .../unix/sysv/linux/kernel-posix-cpu-timers.h | 28 +++++++++++++++----
> sysdeps/unix/sysv/linux/timer_create.c | 4 +--
> 5 files changed, 28 insertions(+), 10 deletions(-)
>
> diff --git a/nptl/pthread_getcpuclockid.c b/nptl/pthread_getcpuclockid.c
> index 344bd6560e..b8bf09f550 100644
> --- a/nptl/pthread_getcpuclockid.c
> +++ b/nptl/pthread_getcpuclockid.c
> @@ -35,7 +35,7 @@ __pthread_getcpuclockid (pthread_t threadid, clockid_t *clockid)
>
> /* The clockid_t value is a simple computation from the TID. */
>
> - const clockid_t tidclock = MAKE_THREAD_CPUCLOCK (pd->tid, CPUCLOCK_SCHED);
> + const clockid_t tidclock = make_thread_cpuclock (pd->tid, CPUCLOCK_SCHED);
>
> *clockid = tidclock;
> return 0;
OK. Use the new function instead of the old macro.
> diff --git a/sysdeps/unix/sysv/linux/clock_getcpuclockid.c b/sysdeps/unix/sysv/linux/clock_getcpuclockid.c
> index 5534127ed7..355d3c86af 100644
> --- a/sysdeps/unix/sysv/linux/clock_getcpuclockid.c
> +++ b/sysdeps/unix/sysv/linux/clock_getcpuclockid.c
> @@ -29,7 +29,7 @@ __clock_getcpuclockid (pid_t pid, clockid_t *clock_id)
> /* The clockid_t value is a simple computation from the PID.
> But we do a clock_getres call to validate it. */
>
> - const clockid_t pidclock = MAKE_PROCESS_CPUCLOCK (pid, CPUCLOCK_SCHED);
> + const clockid_t pidclock = make_process_cpuclock (pid, CPUCLOCK_SCHED);
>
> #ifndef __NR_clock_getres_time64
> # define __NR_clock_getres_time64 __NR_clock_getres
OK. Same.
> diff --git a/sysdeps/unix/sysv/linux/clock_nanosleep.c b/sysdeps/unix/sysv/linux/clock_nanosleep.c
> index befe6ecb8c..e610fd4e8d 100644
> --- a/sysdeps/unix/sysv/linux/clock_nanosleep.c
> +++ b/sysdeps/unix/sysv/linux/clock_nanosleep.c
> @@ -34,7 +34,7 @@ __clock_nanosleep_time64 (clockid_t clock_id, int flags,
> if (clock_id == CLOCK_THREAD_CPUTIME_ID)
> return EINVAL;
> if (clock_id == CLOCK_PROCESS_CPUTIME_ID)
> - clock_id = MAKE_PROCESS_CPUCLOCK (0, CPUCLOCK_SCHED);
> + clock_id = PROCESS_CLOCK;
>
> /* If the call is interrupted by a signal handler or encounters an error,
> it returns a positive value similar to errno. */
OK. PROCESS_CLOCK expands to the appropriate call to make_process_cpuclock.
> diff --git a/sysdeps/unix/sysv/linux/kernel-posix-cpu-timers.h b/sysdeps/unix/sysv/linux/kernel-posix-cpu-timers.h
> index 164a90ddeb..bea1e0e62d 100644
> --- a/sysdeps/unix/sysv/linux/kernel-posix-cpu-timers.h
> +++ b/sysdeps/unix/sysv/linux/kernel-posix-cpu-timers.h
> @@ -1,4 +1,12 @@
> -/* Parameters for the Linux kernel ABI for CPU clocks. */
> +/*
> + Parameters for the Linux kernel ABI for CPU clocks, the bit fields within
> + a clockid:
> +
> + - The most significant 29 bits hold either a pid or a file descriptor.
> + - Bit 2 indicates whether a cpu clock refers to a thread or a process.
> + - Bits 1 and 0 give the type: PROF=0, VIRT=1, SCHED=2, or FD=3.
> + - A clockid is invalid if bits 2, 1, and 0 are all set.
> + */
>
> #define CPUCLOCK_PID(clock) ((pid_t) ~((clock) >> 3))
> #define CPUCLOCK_PERTHREAD(clock) \
OK. Comment lines up with the one in Linux's "include/linux/posix-timers.h".
> @@ -12,7 +20,17 @@
> #define CPUCLOCK_SCHED 2
> #define CPUCLOCK_MAX 3
>
> -#define MAKE_PROCESS_CPUCLOCK(pid, clock) \
> - ((~(clockid_t) (pid) << 3) | (clockid_t) (clock))
OK. clockid_t is a signed type, thus expanding with pid = 0 leads to a
left-shift on a negative value.
> -#define MAKE_THREAD_CPUCLOCK(tid, clock) \
> - MAKE_PROCESS_CPUCLOCK((tid), (clock) | CPUCLOCK_PERTHREAD_MASK)
OK. Same macro used. Same issue.
> +static inline clockid_t
> +make_process_cpuclock (unsigned int pid, clockid_t clock)
> +{
> + return ((~pid) << 3) | clock;
> +}
> +
OK. Replacement function that uses unsigned. Lines up with the version
in Linux's sources.
> +static inline clockid_t
> +make_thread_cpuclock (unsigned int tid, clockid_t clock)
> +{
> + return make_process_cpuclock (tid, clock | CPUCLOCK_PERTHREAD_MASK);
> +}
> +
OK. Replaces the second macro for tid.
> +#define PROCESS_CLOCK make_process_cpuclock (0, CPUCLOCK_SCHED)
> +#define THREAD_CLOCK make_thread_cpuclock (0, CPUCLOCK_SCHED)
OK. Macros for convenience.
> diff --git a/sysdeps/unix/sysv/linux/timer_create.c b/sysdeps/unix/sysv/linux/timer_create.c
> index a8b2a41d9e..290324a7ea 100644
> --- a/sysdeps/unix/sysv/linux/timer_create.c
> +++ b/sysdeps/unix/sysv/linux/timer_create.c
> @@ -33,9 +33,9 @@ ___timer_create (clockid_t clock_id, struct sigevent *evp, timer_t *timerid)
> {
> {
> clockid_t syscall_clockid = (clock_id == CLOCK_PROCESS_CPUTIME_ID
> - ? MAKE_PROCESS_CPUCLOCK (0, CPUCLOCK_SCHED)
> + ? PROCESS_CLOCK
> : clock_id == CLOCK_THREAD_CPUTIME_ID
> - ? MAKE_THREAD_CPUCLOCK (0, CPUCLOCK_SCHED)
> + ? THREAD_CLOCK
> : clock_id);
>
> /* If the user wants notification via a thread we need to handle
OK. Use the new macros.
On 17/10/22 19:33, Arjun Shankar wrote:
> Hi Adhemerval,
>
>> The current macros uses pid as signed value, which triggers a compiler
>> warning for process and thread timers. Replace MAKE_PROCESS_CPUCLOCK
>> with static inline function that expects the pid as unsigned. These
>> are similar to what Linux does internally.
>>
>> Checked on x86_64-linux-gnu.
>
> I tried building master with -Wshift-negative-value and ran into a
> couple of other left-shifts on negative values in
> sysdeps/x86/dl-cacheinfo.h:
That's a good experiment, I see that clang enables it as default.
>
>> count_mask = ~(-1 << (count_mask + 1));
>
> Perhaps a cast of the -1 to unsigned here would make the intent even
> more clear, and get glibc building cleanly with
> -Wshift-negative-value. What do you think?
I think we can also make the mask unsigned to avoid a potential UB
and remove the inline assembly since we have a proper builtin for it:
unsigned int count_mask = __builtin_clz (threads_l2);
count_mask = ~(-1U << (count_mask + 1));
>
> Anyway, this patch itself looks good to me.
>
> Reviewed-by: Arjun Shankar <arjun@redhat.com>
Thanks.
>
>> nptl/pthread_getcpuclockid.c | 2 +-
>> sysdeps/unix/sysv/linux/clock_getcpuclockid.c | 2 +-
>> sysdeps/unix/sysv/linux/clock_nanosleep.c | 2 +-
>> .../unix/sysv/linux/kernel-posix-cpu-timers.h | 28 +++++++++++++++----
>> sysdeps/unix/sysv/linux/timer_create.c | 4 +--
>> 5 files changed, 28 insertions(+), 10 deletions(-)
>>
>> diff --git a/nptl/pthread_getcpuclockid.c b/nptl/pthread_getcpuclockid.c
>> index 344bd6560e..b8bf09f550 100644
>> --- a/nptl/pthread_getcpuclockid.c
>> +++ b/nptl/pthread_getcpuclockid.c
>> @@ -35,7 +35,7 @@ __pthread_getcpuclockid (pthread_t threadid, clockid_t *clockid)
>>
>> /* The clockid_t value is a simple computation from the TID. */
>>
>> - const clockid_t tidclock = MAKE_THREAD_CPUCLOCK (pd->tid, CPUCLOCK_SCHED);
>> + const clockid_t tidclock = make_thread_cpuclock (pd->tid, CPUCLOCK_SCHED);
>>
>> *clockid = tidclock;
>> return 0;
>
> OK. Use the new function instead of the old macro.
>
>> diff --git a/sysdeps/unix/sysv/linux/clock_getcpuclockid.c b/sysdeps/unix/sysv/linux/clock_getcpuclockid.c
>> index 5534127ed7..355d3c86af 100644
>> --- a/sysdeps/unix/sysv/linux/clock_getcpuclockid.c
>> +++ b/sysdeps/unix/sysv/linux/clock_getcpuclockid.c
>> @@ -29,7 +29,7 @@ __clock_getcpuclockid (pid_t pid, clockid_t *clock_id)
>> /* The clockid_t value is a simple computation from the PID.
>> But we do a clock_getres call to validate it. */
>>
>> - const clockid_t pidclock = MAKE_PROCESS_CPUCLOCK (pid, CPUCLOCK_SCHED);
>> + const clockid_t pidclock = make_process_cpuclock (pid, CPUCLOCK_SCHED);
>>
>> #ifndef __NR_clock_getres_time64
>> # define __NR_clock_getres_time64 __NR_clock_getres
>
> OK. Same.
>
>> diff --git a/sysdeps/unix/sysv/linux/clock_nanosleep.c b/sysdeps/unix/sysv/linux/clock_nanosleep.c
>> index befe6ecb8c..e610fd4e8d 100644
>> --- a/sysdeps/unix/sysv/linux/clock_nanosleep.c
>> +++ b/sysdeps/unix/sysv/linux/clock_nanosleep.c
>> @@ -34,7 +34,7 @@ __clock_nanosleep_time64 (clockid_t clock_id, int flags,
>> if (clock_id == CLOCK_THREAD_CPUTIME_ID)
>> return EINVAL;
>> if (clock_id == CLOCK_PROCESS_CPUTIME_ID)
>> - clock_id = MAKE_PROCESS_CPUCLOCK (0, CPUCLOCK_SCHED);
>> + clock_id = PROCESS_CLOCK;
>>
>> /* If the call is interrupted by a signal handler or encounters an error,
>> it returns a positive value similar to errno. */
>
> OK. PROCESS_CLOCK expands to the appropriate call to make_process_cpuclock.
>
>> diff --git a/sysdeps/unix/sysv/linux/kernel-posix-cpu-timers.h b/sysdeps/unix/sysv/linux/kernel-posix-cpu-timers.h
>> index 164a90ddeb..bea1e0e62d 100644
>> --- a/sysdeps/unix/sysv/linux/kernel-posix-cpu-timers.h
>> +++ b/sysdeps/unix/sysv/linux/kernel-posix-cpu-timers.h
>> @@ -1,4 +1,12 @@
>> -/* Parameters for the Linux kernel ABI for CPU clocks. */
>> +/*
>> + Parameters for the Linux kernel ABI for CPU clocks, the bit fields within
>> + a clockid:
>> +
>> + - The most significant 29 bits hold either a pid or a file descriptor.
>> + - Bit 2 indicates whether a cpu clock refers to a thread or a process.
>> + - Bits 1 and 0 give the type: PROF=0, VIRT=1, SCHED=2, or FD=3.
>> + - A clockid is invalid if bits 2, 1, and 0 are all set.
>> + */
>>
>> #define CPUCLOCK_PID(clock) ((pid_t) ~((clock) >> 3))
>> #define CPUCLOCK_PERTHREAD(clock) \
>
> OK. Comment lines up with the one in Linux's "include/linux/posix-timers.h".
>
>> @@ -12,7 +20,17 @@
>> #define CPUCLOCK_SCHED 2
>> #define CPUCLOCK_MAX 3
>>
>> -#define MAKE_PROCESS_CPUCLOCK(pid, clock) \
>> - ((~(clockid_t) (pid) << 3) | (clockid_t) (clock))
>
> OK. clockid_t is a signed type, thus expanding with pid = 0 leads to a
> left-shift on a negative value.
>
>> -#define MAKE_THREAD_CPUCLOCK(tid, clock) \
>> - MAKE_PROCESS_CPUCLOCK((tid), (clock) | CPUCLOCK_PERTHREAD_MASK)
>
> OK. Same macro used. Same issue.
>
>> +static inline clockid_t
>> +make_process_cpuclock (unsigned int pid, clockid_t clock)
>> +{
>> + return ((~pid) << 3) | clock;
>> +}
>> +
>
> OK. Replacement function that uses unsigned. Lines up with the version
> in Linux's sources.
>
>> +static inline clockid_t
>> +make_thread_cpuclock (unsigned int tid, clockid_t clock)
>> +{
>> + return make_process_cpuclock (tid, clock | CPUCLOCK_PERTHREAD_MASK);
>> +}
>> +
>
> OK. Replaces the second macro for tid.
>
>> +#define PROCESS_CLOCK make_process_cpuclock (0, CPUCLOCK_SCHED)
>> +#define THREAD_CLOCK make_thread_cpuclock (0, CPUCLOCK_SCHED)
>
> OK. Macros for convenience.
>
>> diff --git a/sysdeps/unix/sysv/linux/timer_create.c b/sysdeps/unix/sysv/linux/timer_create.c
>> index a8b2a41d9e..290324a7ea 100644
>> --- a/sysdeps/unix/sysv/linux/timer_create.c
>> +++ b/sysdeps/unix/sysv/linux/timer_create.c
>> @@ -33,9 +33,9 @@ ___timer_create (clockid_t clock_id, struct sigevent *evp, timer_t *timerid)
>> {
>> {
>> clockid_t syscall_clockid = (clock_id == CLOCK_PROCESS_CPUTIME_ID
>> - ? MAKE_PROCESS_CPUCLOCK (0, CPUCLOCK_SCHED)
>> + ? PROCESS_CLOCK
>> : clock_id == CLOCK_THREAD_CPUTIME_ID
>> - ? MAKE_THREAD_CPUCLOCK (0, CPUCLOCK_SCHED)
>> + ? THREAD_CLOCK
>> : clock_id);
>>
>> /* If the user wants notification via a thread we need to handle
>
> OK. Use the new macros.
>
@@ -35,7 +35,7 @@ __pthread_getcpuclockid (pthread_t threadid, clockid_t *clockid)
/* The clockid_t value is a simple computation from the TID. */
- const clockid_t tidclock = MAKE_THREAD_CPUCLOCK (pd->tid, CPUCLOCK_SCHED);
+ const clockid_t tidclock = make_thread_cpuclock (pd->tid, CPUCLOCK_SCHED);
*clockid = tidclock;
return 0;
@@ -29,7 +29,7 @@ __clock_getcpuclockid (pid_t pid, clockid_t *clock_id)
/* The clockid_t value is a simple computation from the PID.
But we do a clock_getres call to validate it. */
- const clockid_t pidclock = MAKE_PROCESS_CPUCLOCK (pid, CPUCLOCK_SCHED);
+ const clockid_t pidclock = make_process_cpuclock (pid, CPUCLOCK_SCHED);
#ifndef __NR_clock_getres_time64
# define __NR_clock_getres_time64 __NR_clock_getres
@@ -34,7 +34,7 @@ __clock_nanosleep_time64 (clockid_t clock_id, int flags,
if (clock_id == CLOCK_THREAD_CPUTIME_ID)
return EINVAL;
if (clock_id == CLOCK_PROCESS_CPUTIME_ID)
- clock_id = MAKE_PROCESS_CPUCLOCK (0, CPUCLOCK_SCHED);
+ clock_id = PROCESS_CLOCK;
/* If the call is interrupted by a signal handler or encounters an error,
it returns a positive value similar to errno. */
@@ -1,4 +1,12 @@
-/* Parameters for the Linux kernel ABI for CPU clocks. */
+/*
+ Parameters for the Linux kernel ABI for CPU clocks, the bit fields within
+ a clockid:
+
+ - The most significant 29 bits hold either a pid or a file descriptor.
+ - Bit 2 indicates whether a cpu clock refers to a thread or a process.
+ - Bits 1 and 0 give the type: PROF=0, VIRT=1, SCHED=2, or FD=3.
+ - A clockid is invalid if bits 2, 1, and 0 are all set.
+ */
#define CPUCLOCK_PID(clock) ((pid_t) ~((clock) >> 3))
#define CPUCLOCK_PERTHREAD(clock) \
@@ -12,7 +20,17 @@
#define CPUCLOCK_SCHED 2
#define CPUCLOCK_MAX 3
-#define MAKE_PROCESS_CPUCLOCK(pid, clock) \
- ((~(clockid_t) (pid) << 3) | (clockid_t) (clock))
-#define MAKE_THREAD_CPUCLOCK(tid, clock) \
- MAKE_PROCESS_CPUCLOCK((tid), (clock) | CPUCLOCK_PERTHREAD_MASK)
+static inline clockid_t
+make_process_cpuclock (unsigned int pid, clockid_t clock)
+{
+ return ((~pid) << 3) | clock;
+}
+
+static inline clockid_t
+make_thread_cpuclock (unsigned int tid, clockid_t clock)
+{
+ return make_process_cpuclock (tid, clock | CPUCLOCK_PERTHREAD_MASK);
+}
+
+#define PROCESS_CLOCK make_process_cpuclock (0, CPUCLOCK_SCHED)
+#define THREAD_CLOCK make_thread_cpuclock (0, CPUCLOCK_SCHED)
@@ -33,9 +33,9 @@ ___timer_create (clockid_t clock_id, struct sigevent *evp, timer_t *timerid)
{
{
clockid_t syscall_clockid = (clock_id == CLOCK_PROCESS_CPUTIME_ID
- ? MAKE_PROCESS_CPUCLOCK (0, CPUCLOCK_SCHED)
+ ? PROCESS_CLOCK
: clock_id == CLOCK_THREAD_CPUTIME_ID
- ? MAKE_THREAD_CPUCLOCK (0, CPUCLOCK_SCHED)
+ ? THREAD_CLOCK
: clock_id);
/* If the user wants notification via a thread we need to handle