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LibC: Improve error handling for unimplemented functions #26514

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LibC: Improve error handling for unimplemented functions #26514

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@po-nuvai po-nuvai commented Dec 29, 2025

This PR improves error handling for several unimplemented LibC functions:

  • getpriority()/setpriority(): Set errno to ENOSYS before returning -1
  • chroot(): Set errno to ENOSYS before returning -1
  • nice(): Set errno to ENOSYS and return -1 (was incorrectly returning the incr argument)
  • fnmatch(): Return FNM_NOMATCH instead of 0 (which falsely indicates a match)

These functions now properly indicate they are not implemented by setting errno to ENOSYS, following POSIX conventions.

@github-actions github-actions bot added the 👀 pr-needs-review PR needs review from a maintainer or community member label Dec 29, 2025
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BuggieBot commented Dec 29, 2025

Hello!

One or more of the commit messages in this PR do not match the SerenityOS code submission policy, please check the lint_commits CI job for more details on which commits were flagged and why.
Please do not close this PR and open another, instead modify your commit message(s) with git commit --amend and force push those changes to update this PR.

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LibC: Set errno to ENOSYS for unimplemented stub functions
1e36e9e 
Set errno to ENOSYS before returning -1 in getpriority(), setpriority(),
chroot(), and nice() stubs. Also fix nice() to return -1 instead of the
incr argument, and fnmatch() to return FNM_NOMATCH instead of 0.
@po-nuvai po-nuvai force-pushed the libc-stub-errno-fix branch from 0f6d355 to 1e36e9e Compare December 29, 2025 12:59
spholz
spholz reviewed Dec 29, 2025
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Userland/Libraries/LibC/fnmatch.cpp
// https://pubs.opengroup.org/onlinepubs/9699919799/functions/fnmatch.html
int fnmatch([[maybe_unused]] char const* pattern, [[maybe_unused]] char const* string, [[maybe_unused]] int flags)
{
dbgln("FIXME: Implement fnmatch()");
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@spholz spholz Dec 29, 2025

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I would keep these FIXME dbglns. Having this output makes it easier to debug ports that attempt to use these functions and fail because we don't implement them yet.

@nico nico added ⏳ pr-waiting-for-author PR is blocked by feedback / code changes from the author and removed 👀 pr-needs-review PR needs review from a maintainer or community member labels Dec 29, 2025
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oskar-skog commented Dec 30, 2025 •
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According to POSIX, fnmatch should return a non-zero value other than FNM_NOMATCH to indicate an error.
https://pubs.opengroup.org/onlinepubs/9799919799/functions/fnmatch.html

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stale bot commented Jan 21, 2026

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed in 7 days if no further activity occurs. Thank you for your contributions!

@stale stale bot added the stale label Jan 21, 2026
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