On 2025-09-21 19:13:23+0200, Willy Tarreau wrote:
On Sun, Sep 21, 2025 at 07:05:24PM +0200, Benjamin Berg wrote:
This also ties to the question of the other mail. I prefer "errno" not to be available if it is not actually safe to use. UML does use threads in some places (and may use it extensively in the future). The current "errno" implementation is not threadsafe and I see neither an obvious way nor a need to change that. By setting NOLIBC_IGNORE_ERRNO any unsafe code will not compile and can be changed to use the sys_* functions to avoid errno.
That's the point I disagree with because here we're not using errno more than printf() or dirent(). Why fix dirent() to build without errno and break perror() ? Why not also break printf() then ? All of this must be consistent. We're unbreaking some arbitrary functions and breaking other arbitrary ones, that's not logical.
printf() is already broken. So by breaking perror() it would have been consistent :-/.
I'm totally fine with saying that errno shouldn't be defined when building without errno, but all functions must continue to be defined. perror() is used to print an error message, it's a valid use case just as printf() and should remain.
If we disable perror for this, then we must also disable usage of printf for consistency (and I don't want this either).
Then let's also fix printf(). Benjamin, do you want to add this to your series? It should be consitent with the perror() fallback.
Thomas