[PATCH 2/2] futex.2: Use appropriate types

From: Alejandro Colomar
Date: Fri Oct 30 2020 - 08:40:14 EST


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.

Signed-off-by: Alejandro Colomar <colomar.6.4.3@xxxxxxxxx>
---
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)
--
2.28.0