acassis opened a new pull request, #20419:
URL: https://github.com/apache/nuttx/pull/20419
## Summary
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.
## Impact
Now opening /proc will work on AVR and on my retro computing CDP1802 port.
## Testing
```
$ cdp1802-unknown-elf-sim --rom nuttx.elf.bin --rom-size 32768 --banks 16
--symbols nuttx.elf
NuttShell (NSH) NuttX-13.1.0-RC0
nsh> ?
?
help usage: help [-v] [<cmd>]
? help quit uptime
free poweroff ps
nsh> free
free
total used free maxused maxfree nused nfree name
14376 3576 10800 4512 10000 16 2 Umem
nsh>
```
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