Am Montag, dem 23.02.2026 um 14:30 -0500 schrieb Yair Lenga via Gcc: > Hi GCC maintainers, > > I’d like feedback on a small, C-only attribute proposal to improve > practicality of using -Wvla in large codebases. > Motivation > > Projects often enable -Wvla (sometimes with -Werror=vla) to discourage > unbounded VLAs. However, there are occasional VLAs that are intentionally > bounded/validated (e.g., small scratch buffers sized from known limits). > Today, suppressing -Wvla locally requires #pragma GCC diagnostic > push/ignored/pop, which is verbose and harder to keep correct during > refactoring. > > I’m looking for a declaration-scoped, readable opt-out similar in spirit to > [[fallthrough]]: keep the warning enabled globally, but allow a > clearly-marked exception at a specific declaration. > Proposal (C only) > > Introduce a GNU C attribute: > > [[gnu::allow_vla]] char tmp[n]; > > (Spelling is flexible; I mainly want the functionality. I’m fine with > __attribute__((allow_vla)) as well, but [[gnu::...]] is pleasant in C23 > style.) > Semantics > > When -Wvla is enabled, a VLA declaration annotated with [[gnu::allow_vla]] > does *not* emit the -Wvla warning for that declaration. > > Non-goals: > > - > > No change to VLA semantics, ABI, or code generation. > - > > Not a general “suppress any warning” attribute. > - > > C-only (no C++ support requested). > > Scope restrictions (to reduce ambiguity) > > I suggest restricting the attribute to: > > - > > object declarations with automatic storage duration (typical VLA usage), > and > - > > only affecting the -Wvla diagnostic for that declaration. > > (If maintainers prefer broader applicability, I can adjust, but I’d like to > start minimal.) > Implementation sketch > > My assumption is: > > - > > parse/attach the attribute to the relevant DECL (e.g., DECL_ATTRIBUTES), > - > > and gate the -Wvla diagnostic emission on “decl has allow_vla”. > > I can provide a patch + tests once there is agreement on direction and > naming. > Questions > > 1. > > Is a dedicated C-only GNU attribute acceptable for this purpose, vs. > insisting on #pragma GCC diagnostic?
I assume you want something more lightweight than #pragma GCC diagnostic ignored "-Wvla" ? > 2. > > Preferred spelling/name: allow_vla, vla_ok, etc.? > 3. > > I intentionally propose -Wvla suppression only; I’m not requesting > suppression of -Wvla-larger-than=. What I do not fully understand is why -Wvla-larger-than= does not do what you want already if you are interested in small bounded VLAs? Martin > > Thanks, > Yair
