linux-kernel - Re: [PATCH 2/2] futex.2: Use appropriate types

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Message-ID: <f556e3a4-8120-b57c-8da1-7a2273b5fd78@gmail.com>
Date:   Fri, 30 Oct 2020 20:19:26 +0100
From:   "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:     Alejandro Colomar <colomar.6.4.3@...il.com>
Cc:     mtk.manpages@...il.com, linux-man@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] futex.2: Use appropriate types

On 10/30/20 1:39 PM, Alejandro Colomar wrote:
> The Linux kernel uses the following:
> 
> kernel/futex.c:3778:
> SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
> 		struct __kernel_timespec __user *, utime, u32 __user *, uaddr2,
> 		u32, val3)
> 
> Since there is no glibc wrapper, use the same types the kernel uses.

Thanks. Patch applied.

Cheers,

Michael

> Signed-off-by: Alejandro Colomar <colomar.6.4.3@...il.com>
> ---
>  man2/futex.2 | 27 ++++++++++++++-------------
>  1 file changed, 14 insertions(+), 13 deletions(-)
> 
> diff --git a/man2/futex.2 b/man2/futex.2
> index 837adbd25..73de71623 100644
> --- a/man2/futex.2
> +++ b/man2/futex.2
> @@ -26,12 +26,13 @@ futex \- fast user-space locking
>  .nf
>  .PP
>  .B #include <linux/futex.h>
> +.B #include <stdint.h>
>  .B #include <sys/time.h>
>  .PP
> -.BI "int futex(int *" uaddr ", int " futex_op ", int " val ,
> +.BI "long futex(uint32_t *" uaddr ", int " futex_op ", uint32_t " val ,
>  .BI "          const struct timespec *" timeout , \
>  " \fR  /* or: \fBuint32_t \fIval2\fP */"
> -.BI "          int *" uaddr2 ", int " val3 );
> +.BI "          uint32_t *" uaddr2 ", uint32_t " val3 );
>  .fi
>  .PP
>  .IR Note :
> @@ -581,8 +582,8 @@ any of the two supplied futex words:
>  .IP
>  .in +4n
>  .EX
> -int oldval = *(int *) uaddr2;
> -*(int *) uaddr2 = oldval \fIop\fP \fIoparg\fP;
> +uint32_t oldval = *(uint32_t *) uaddr2;
> +*(uint32_t *) uaddr2 = oldval \fIop\fP \fIoparg\fP;
>  futex(uaddr, FUTEX_WAKE, val, 0, 0, 0);
>  if (oldval \fIcmp\fP \fIcmparg\fP)
>      futex(uaddr2, FUTEX_WAKE, val2, 0, 0, 0);
> @@ -1765,11 +1766,11 @@ Child  (18535) 4
>  #define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \e
>                          } while (0)
>  
> -static int *futex1, *futex2, *iaddr;
> +static uint32_t *futex1, *futex2, *iaddr;
>  
>  static int
> -futex(int *uaddr, int futex_op, int val,
> -      const struct timespec *timeout, int *uaddr2, int val3)
> +futex(uint32_t *uaddr, int futex_op, uint32_t val,
> +      const struct timespec *timeout, uint32_t *uaddr2, uint32_t val3)
>  {
>      return syscall(SYS_futex, uaddr, futex_op, val,
>                     timeout, uaddr2, val3);
> @@ -1779,9 +1780,9 @@ futex(int *uaddr, int futex_op, int val,
>     become 1, and then set the value to 0. */
>  
>  static void
> -fwait(int *futexp)
> +fwait(uint32_t *futexp)
>  {
> -    int s;
> +    long s;
>  
>      /* atomic_compare_exchange_strong(ptr, oldval, newval)
>         atomically performs the equivalent of:
> @@ -1794,7 +1795,7 @@ fwait(int *futexp)
>      while (1) {
>  
>          /* Is the futex available? */
> -        const int one = 1;
> +        const uint32_t one = 1;
>          if (atomic_compare_exchange_strong(futexp, &one, 0))
>              break;      /* Yes */
>  
> @@ -1811,13 +1812,13 @@ fwait(int *futexp)
>     so that if the peer is blocked in fpost(), it can proceed. */
>  
>  static void
> -fpost(int *futexp)
> +fpost(uint32_t *futexp)
>  {
> -    int s;
> +    long s;
>  
>      /* atomic_compare_exchange_strong() was described in comments above */
>  
> -    const int zero = 0;
> +    const uint32_t zero = 0;
>      if (atomic_compare_exchange_strong(futexp, &zero, 1)) {
>          s = futex(futexp, FUTEX_WAKE, 1, NULL, NULL, 0);
>          if (s  == \-1)
> 


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/