O_DIRECTORY, O_NOFOLLOW, O_NOATIME, O_CLOEXEC, __O_SYNC, O_PATH and
__O_TMPFILE are defined as shifts by 16 to 22 bits. Where int is 16
bits (AVR, for example), these shifts exceed the width of the type:
GCC evaluates them to 0, and the -Wshift-count-overflow warning is not
shown because include/ is a system include directory. The oflags
argument of open() is an int, so it could not carry those bits anyway.
As a result, on arch with int equal 16-bit opendir() opens directories
without O_DIRECTORY, so opening a mount point such as /proc fails with
ENOENT, and O_CLOEXEC and O_NOFOLLOW have no effect.
When UINT_MAX is 0xffff, use the unused bits 2 to 4 for O_DIRECTORY,
O_CLOEXEC and O_NOFOLLOW, define O_NOATIME and __O_SYNC as 0 (O_SYNC
falls back to O_DSYNC), and leave O_PATH and O_TMPFILE undefined, so
that code which needs them fails to build instead of silently opening
with the wrong flags; nothing in the tree uses them. _O_MAXBIT becomes
15. On bigger systems (32-bit, 64-bit) keep the original bit shift.
Signed-off-by: Alan Carvalho de Assis <acassis@gmail.com>
Assisted-by: Claude Opus 5.5 (claude-opus-5-5)
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