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Merge branch 'old-linux-kernel-futex' into 'main'

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gthread-posix: fix build against very old Linux headers

Closes #2861

See merge request GNOME/glib!3370
This commit is contained in:
Philip Withnall 2023-04-11 11:10:28 +00:00
commit 93168d5319
1 changed files with 20 additions and 7 deletions
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27
glib/gthread-posix.c
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@ -1523,16 +1523,18 @@ g_cond_wait_until (GCond *cond,
* have any relation to the one used by the kernel for the `futex` syscall.
*
* Specifically, the libc headers might use 64-bit `time_t` while the kernel
* headers use 32-bit `__kernel_old_time_t` on certain systems.
* headers use 32-bit types on certain systems.
*
* To get around this problem we
* a) check if `futex_time64` is available, which only exists on 32-bit
* platforms and always uses 64-bit `time_t`.
* b) otherwise (or if that returns `ENOSYS`), we call the normal `futex`
* syscall with the `struct timespec` used by the kernel, which uses
* `__kernel_long_t` for both its fields. We use that instead of
* `__kernel_old_time_t` because it is equivalent and available in the
* kernel headers for a longer time.
* syscall with the `struct timespec` used by the kernel. By default, we
* use `__kernel_long_t` for both its fields, which is equivalent to
* `__kernel_old_time_t` and is available in the kernel headers for a
* longer time.
* c) With very old headers (~2.6.x), `__kernel_long_t` is not available, and
* we use an older definition that uses `__kernel_time_t` and `long`.
*
* Also some 32-bit systems do not define `__NR_futex` at all and only
* define `__NR_futex_time64`.
@ -1572,14 +1574,24 @@ g_cond_wait_until (GCond *cond,
#ifdef __NR_futex
{
# ifdef __kernel_long_t
# define KERNEL_SPAN_SEC_TYPE __kernel_long_t
struct
{
__kernel_long_t tv_sec;
__kernel_long_t tv_nsec;
} span_arg;
# else
/* Very old kernel headers: version 2.6.32 and thereabouts */
# define KERNEL_SPAN_SEC_TYPE __kernel_time_t
struct
{
__kernel_time_t tv_sec;
long tv_nsec;
} span_arg;
# endif
/* Make sure to only ever call this if the end time actually fits into the target type */
if (G_UNLIKELY (sizeof (__kernel_long_t) < 8 && span.tv_sec > G_MAXINT32))
if (G_UNLIKELY (sizeof (KERNEL_SPAN_SEC_TYPE) < 8 && span.tv_sec > G_MAXINT32))
g_error ("%s: Can’t wait for more than %us", G_STRFUNC, G_MAXINT32);
span_arg.tv_sec = span.tv_sec;
@ -1591,6 +1603,7 @@ g_cond_wait_until (GCond *cond,
return success;
}
# undef KERNEL_SPAN_SEC_TYPE
#endif /* defined(__NR_futex) */
/* We can't end up here because of the checks above */