idtools: avoid direct use of C.stderr to fix musl cgo build failures #559
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podmanbot
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Dec 18, 2025
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✅ A new PR has been created in buildah to vendor these changes: containers/buildah#6606 |
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Thanks! Code LGTM.
Could you add at least some summary of the (great) description in the commit message also as a comment directly to the subid_stderr function, please? I’m worried that in a few years, someone (like me) might “simplify” this code without carefully studying the commit history to understand the rationale.
On musl-based systems, stderr is declared as FILE *const. Referencing stderr directly from Go code (via C.stderr) causes cgo to generate assignment code for a const-qualified pointer, which is invalid C and fails to compile. Both gcc and clang reject the generated code with error messages below: clang: > cgo-gcc-prolog:85:9: error: cannot assign to variable '_cgo_r' with const-qualified type 'typeof (_cgo_a->r)' (aka 'struct _IO_FILE *const') > cgo-gcc-prolog:83:24: note: variable '_cgo_r' declared const here > cgo-gcc-prolog:88:12: error: cannot assign to non-static data member 'r' with const-qualified type 'FILE *const' (aka 'struct _IO_FILE *const') > cgo-gcc-prolog:80:15: note: non-static data member 'r' declared const here gcc: > cgo-gcc-prolog:85:9: error: assignment of read-only variable '_cgo_r' > cgo-gcc-prolog:88:12: error: assignment of read-only member 'r' This patch avoids referencing C.stderr from Go code and instead returns stderr from a small C helper function. This keeps the usage entirely in C and avoids cgo’s broken handling for const-qualified global objects. Signed-off-by: Z. Liu <zhixu.liu@gmail.com>
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the problem had been fixed by go side (in 1.26 branch) too, see commit https://go.googlesource.com/go/+/7a6e3f07acfd822aa1d62f1c715125e30d67d089%5E%21/ |
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On musl-based systems, stderr is declared as FILE *const.
Referencing stderr directly from Go code (via C.stderr) causes cgo to generate assignment code for a const-qualified pointer, which is invalid C and fails to compile.
Both gcc and clang reject the generated code with error messages below:
clang:
gcc:
This patch avoids referencing C.stderr from Go code and instead returns stderr from a small C helper function. This keeps the usage entirely in C and avoids cgo’s broken handling for const-qualified global objects.