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gcc 14 warns -Wreturn-local-addr in builtin_set_at when compiling the amalgamation (main and phase2-numbers)

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
78/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
c, github-actions
Domain
build-system, ci-cd

Research direction

Start in src/builtins.c at builtin_set_at and trace the buffer path through BUILTIN_LIST_VIEW and slot_view. Run make embed-smoke with gcc 14 to reproduce the warning in build/eigenscript_all.c; the issue identifies list_get_ref(arg, 0) as one possible route. Done means the amalgamation builds without -Wreturn-local-addr and the CI extensions / server log has no warning from that file.

Written by the indexing model from the issue text.

Description

area:ci area:runtime-vm bug

Found by the #1758 R1.3 CI-fix builder, 2026-10-19, while reading CI logs. The same warning is present on main.

In CI's extensions / server job (gcc 14.2 in the dev image), make embed-smoke compiles the amalgamation with a warning:

build/eigenscript_all.c: In function 'builtin_set_at':
build/eigenscript_all.c:16782:1: warning: function may return address of local variable [-Wreturn-local-addr]
...
        slot_view(list_slot((list), (i)), &(EigsView){{0}})
...
note: in expansion of macro 'BUILTIN_LIST_VIEW'
        Value *buf = BUILTIN_LIST_VIEW(arg, 0);

It appears on main (run 39269449864 at 965dfbd0, job extensions / server, at 14:31:11Z and 14:32:26Z) and on phase2-numbers (run 39263025702). Local gcc 13.3 does not warn.

By reading the code it is a false positive. builtin_set_at (src/builtins.c, the #1093 buffer path) returns buf only after buf->type == VAL_BUFFER. A buffer is a heap reference, so slot_view returns the reference and not the compound-literal facade. gcc 14 cannot prove that. Still, a warning in a CI lane hides the next real one, and the repository's builds aim at zero warnings.

Done when

  • gcc 14 compiles make embed-smoke (the amalgamation) with no -Wreturn-local-addr warning. For example, the buffer path takes list_get_ref(arg, 0), a real reference, instead of a facade view, or the facade lives in a named local scoped to the function.
  • CI's extensions / server log for the PR shows no warning: line from build/eigenscript_all.c.
Dominant language
C
Stars
3
Forks
7
Avg merge
11h 16m
Merged PRs (30d)
267

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