guarded_by attributes not supported using c++11 style

[nickdesaulniers]

#include <mutex>

class Foo {
    std::mutex m;
    int y __attribute__((guarded_by(m)));
    int z [[clang::guarded_by(m)]];
};

<source>:6:13: warning: unknown attribute 'clang::guarded_by' ignored [-Wunknown-attributes]
    6 |     int z [[clang::guarded_by(m)]];
      |             ^~~~~~~~~~~~~~~~~

[shafik]

CC @erichkeane

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Nick Desaulniers (nickdesaulniers)

```c++ #include <mutex>

class Foo {
std::mutex m;
int y attribute((guarded_by(m)));
int z [[clang::guarded_by(m)]];
};

<source>:6:13: warning: unknown attribute 'clang::guarded_by' ignored [-Wunknown-attributes]
6 | int z [[clang::guarded_by(m)]];
| ^~~~~~~~~~~~~~~~~

</details>

[erichkeane]

This appears intentional? Attr.td has a bunch of attributes that are all ONLY the GNU (or at least, GNU but not one of the CXX/C spellings). For example, pt_guarded_by, acquired_before, acquired_after, etc are all the same.

WE could/should perhaps go through the list an figure out which could be converted to Clang or GCC (if they are because of support by GCC).

I'm not sure, but could this be a good first issue? It is more of 'write a bunch of tests, research what GCC does/has, and figure out which we want the clang spelling for', but requires quite a bit of judgement.

WDYT?

[nickdesaulniers]

This is a clang specific attribute.

…

On Mon, Sep 15, 2025, 6:48 AM Erich Keane ***@***.***> wrote: *erichkeane* left a comment (llvm/llvm-project#158116) <#158116 (comment)> This appears intentional? Attr.td has a bunch of attributes that are all ONLY the GNU (or at least, GNU but not one of the CXX/C spellings). For example, pt_guarded_by, acquired_before, acquired_after, etc are all the same. WE could/should perhaps go through the list an figure out which could be converted to Clang or GCC (if they are because of support by GCC). I'm not sure, but could this be a good first issue? It is more of 'write a bunch of tests, research what GCC does/has, and figure out which we want the clang spelling for', but requires quite a bit of judgement. WDYT? — Reply to this email directly, view it on GitHub <#158116 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAN5IX25GMIKQTNTGJ3DWT33S27S3AVCNFSM6AAAAACGILRH6GVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTEOJSGI3DINZZG4> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[erichkeane]

This is a clang specific attribute.
…

I'm aware THIS one is. I'm saying that this attribute isn't the only one that is going to have this problem, and we should evaluate/solve the whole problem set. This isn't a guarded_by problem, it is a problem with roughly ~25 attributes that were done before the C/C++ spellings were introduced here (or at least, not considering them).

We need to analyze ALL of them to figure out what we want to do (some are going to need Clang spellings, some GCC), and fix them all up.

[llvmbot]

Hi!

This issue may be a good introductory issue for people new to working on LLVM. If you would like to work on this issue, your first steps are:

1. Check that no other contributor is working on this issue. If someone is assigned to the issue or claimed to be working on it, ping the person. After one week without a response, the assignee may be changed.
2. Leave a comment indicating that you are working on the issue, or just create a pull request after following the steps below. Mention this issue in the description of the pull request.
3. Fix the issue locally.
4. Run the test suite locally. Remember that the subdirectories under test/ create fine-grained testing targets, so you can e.g. use make check-clang-ast to only run Clang's AST tests.
5. Create a Git commit.
6. Run git clang-format HEAD~1 to format your changes.
7. Open a pull request to the upstream repository on GitHub. Detailed instructions can be found in GitHub's documentation. Mention this issue in the description of the pull request.

If you have any further questions about this issue, don't hesitate to ask via a comment in the thread below.

[llvmbot]

@llvm/issue-subscribers-good-first-issue

Author: Nick Desaulniers (nickdesaulniers)

```c++ #include <mutex>

class Foo {
std::mutex m;
int y attribute((guarded_by(m)));
int z [[clang::guarded_by(m)]];
};

<source>:6:13: warning: unknown attribute 'clang::guarded_by' ignored [-Wunknown-attributes]
6 | int z [[clang::guarded_by(m)]];
| ^~~~~~~~~~~~~~~~~

</details>