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gthread-posix: fix build against very old Linux headers

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See issue GNOME/glib#2861. Even though (hopefully!) few people are
actually running kernels this old, some build frameworks use very old
kernel headers to try to maximize the portability of their binary
artifacts.
This commit is contained in:
Peter Williams 2023-04-10 10:32:00 -04:00
parent 6834f225f7
commit 1219920fcf
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 */