The kernel uses the following cast:
if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
val2 = (u32) (unsigned long) utime;
This ensures that always the least significant four bytes of the
pointer are used, both on ILP32 and LP64 systems.
On a big endian system a simple cast from 64 bit pointer to 32 bit
integer would return the most significant four bytes.
We have to make the reader of the man-page aware of the usage of the
least significant bytes.
Signed-off-by: Heinrich Schuchardt <xypron.glpk@xxxxxx>
---
man2/futex.2 | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/man2/futex.2 b/man2/futex.2
index 9fd8a51..7732822 100644
--- a/man2/futex.2
+++ b/man2/futex.2
@@ -136,11 +136,13 @@ argument is a pointer to a
.IR timespec
structure that specifies a timeout for the operation.
However, notwithstanding the prototype shown above, for some operations,
-this argument is instead a four-byte integer whose meaning
+the least significant four bytes are used as an integer whose meaning
is determined by the operation.
For these operations, the kernel casts the
.I timeout
-value to
+value first to
+.IR "unsigned long",
+then to
.IR uint32_t ,
and in the remainder of this page, this argument is referred to as
.I val2
--
2.1.4
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