[PATCH] linux: Avoid shifting a negative signed on POSIX timer interface

[PATCH] linux: Avoid shifting a negative signed on POSIX timer interface

[Adhemerval Zanella]

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 | 30 +++++++++++++++----
 sysdeps/unix/sysv/linux/timer_create.c        |  4 +--
 5 files changed, 29 insertions(+), 11 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;
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
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.  */
diff --git a/sysdeps/unix/sysv/linux/kernel-posix-cpu-timers.h b/sysdeps/unix/sysv/linux/kernel-posix-cpu-timers.h
index 164a90ddeb..9c74bb1cf5 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) \
@@ -6,13 +14,23 @@
 #define CPUCLOCK_PID_MASK	7
 #define CPUCLOCK_PERTHREAD_MASK	4
 #define CPUCLOCK_WHICH(clock)	((clock) & (clockid_t) CPUCLOCK_CLOCK_MASK)
-#define CPUCLOCK_CLOCK_MASK	3
+#define CPUCLOCK_CLOCK_MASK	3KE_PROCESS_CPUCLOCK
 #define CPUCLOCK_PROF		0
 #define CPUCLOCK_VIRT		1
 #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)
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
-- 
2.34.1

Re: [PATCH] linux: Avoid shifting a negative signed on POSIX timer interface

[Andreas Schwab]

On Aug 29 2022, Adhemerval Zanella via Libc-alpha wrote:

> @@ -6,13 +14,23 @@
>  #define CPUCLOCK_PID_MASK	7
>  #define CPUCLOCK_PERTHREAD_MASK	4
>  #define CPUCLOCK_WHICH(clock)	((clock) & (clockid_t) CPUCLOCK_CLOCK_MASK)
> -#define CPUCLOCK_CLOCK_MASK	3
> +#define CPUCLOCK_CLOCK_MASK	3KE_PROCESS_CPUCLOCK

Unintentional change.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

Re: [PATCH] linux: Avoid shifting a negative signed on POSIX timer interface

[Andreas Schwab]

On Aug 29 2022, Adhemerval Zanella via Libc-alpha wrote:

> @@ -6,13 +14,23 @@
>  #define CPUCLOCK_PID_MASK	7
>  #define CPUCLOCK_PERTHREAD_MASK	4
>  #define CPUCLOCK_WHICH(clock)	((clock) & (clockid_t) CPUCLOCK_CLOCK_MASK)
> -#define CPUCLOCK_CLOCK_MASK	3
> +#define CPUCLOCK_CLOCK_MASK	3KE_PROCESS_CPUCLOCK

Unintentional change.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."