randomenv: Fix MinGW dllimport warning for `environ`

l0rinc commented at 1:14 am on October 8, 2025: contributor

Extends 7703884 to guard environ declaration on all Windows builds, not just MSVC. llvm-mingw also defines environ as a macro that expands to a dllimport function, causing the same inconsistent linkage warning.

Use WIN32 instead of _MSC_VER to match the platform-specific guards already used throughout the file.

The warning occurs with llvm-mingw (both UCRT and MSVCRT variants as tested by Hebasto), but not with the mingw-w64 toolchain currently used in CI (as mentioned by fanquake).

The error was reproduced by adding a temporary nightly build pointing to https://github.com/l0rinc/bitcoin/pull/45. On master the failure can be seen in https://github.com/l0rinc/bitcoin-core-nightly/pull/2

before: https://github.com/l0rinc/bitcoin-core-nightly/actions/runs/18327936488/job/52196728885?pr=2

 0/home/runner/work/bitcoin-core-nightly/bitcoin-core-nightly/src/randomenv.cpp:61:15: warning: '__p__environ' redeclared without 'dllimport' attribute: previous 'dllimport' ignored [-Winconsistent-dllimport]
 1   61 | extern char** environ; // NOLINT(readability-redundant-declaration): Necessary on some platforms
 2      |               ^
 3/home/runner/work/bitcoin-core-nightly/bitcoin-core-nightly/llvm_mingw_toolchain/aarch64-w64-mingw32/include/stdlib.h:656:17: note: expanded from macro 'environ'
 4  656 | #define environ _environ
 5      |                 ^
 6/home/runner/work/bitcoin-core-nightly/bitcoin-core-nightly/llvm_mingw_toolchain/aarch64-w64-mingw32/include/stdlib.h:225:21: note: expanded from macro '_environ'
 7  225 | #define _environ (* __p__environ())
 8      |                     ^
 9/home/runner/work/bitcoin-core-nightly/bitcoin-core-nightly/llvm_mingw_toolchain/aarch64-w64-mingw32/include/stdlib.h:221:27: note: previous declaration is here
10  221 |   _CRTIMP char ***__cdecl __p__environ(void);
11      |                           ^
12/home/runner/work/bitcoin-core-nightly/bitcoin-core-nightly/llvm_mingw_toolchain/aarch64-w64-mingw32/include/stdlib.h:221:3: note: previous attribute is here
13  221 |   _CRTIMP char ***__cdecl __p__environ(void);
14      |   ^
15/home/runner/work/bitcoin-core-nightly/bitcoin-core-nightly/llvm_mingw_toolchain/aarch64-w64-mingw32/include/_mingw.h:52:40: note: expanded from macro '_CRTIMP'
16   52 | #      define _CRTIMP  __attribute__ ((__dllimport__))
17      |                                        ^
181 warning generated.

after: https://github.com/l0rinc/bitcoin-core-nightly/actions/runs/18329616268/job/52201940831?pr=4

0[ 28%] Building CXX object src/util/CMakeFiles/bitcoin_util.dir/__/randomenv.cpp.obj

Note that there are some other remaining warnings in the logs that will be fixed in separate PRs

randomenv: Fix MinGW dllimport warning for `environ`

Extends 7703884a to guard environ declaration on all Windows builds, not just MSVC.
MinGW also defines environ as a macro that expands to a dllimport function, causing the same inconsistent linkage warning.

Use WIN32 instead of _MSC_VER to match the platform-specific guards already used throughout the file.

Co-authored-by: Hennadii Stepanov <32963518+hebasto@users.noreply.github.com>

97762b1fcf

DrahtBot commented at 1:14 am on October 8, 2025: contributor

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For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/33570.

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maflcko added the label DrahtBot Guix build requested on Oct 8, 2025

fanquake commented at 9:05 am on October 8, 2025: member

MinGW also defines environ … causing the same inconsistent linkage warning.

Can you improve the PR description & commit message? We use mingw-w64 in the CI & Guix build, and it doesn’t produce this warning.

hebasto commented at 11:30 am on October 8, 2025: member

Extends 7703884 to guard environ declaration on all Windows builds, not just MSVC. MinGW also defines environ as a macro that expands to a dllimport function, causing the same inconsistent linkage warning.

~~I suppose this behaviour is specific to UCRT.~~

UPDATE. It is not. I tested the MSVCRT variant of the LLVM MinGW toolchain.

l0rinc commented at 5:41 pm on October 8, 2025: contributor

Thanks for the replies, I have updated the description to clarify this is llvm-mingw specific, let me know if that’s enough.

DrahtBot commented at 1:29 am on October 9, 2025: contributor

Guix builds (on x86_64) [untrusted test-only build, possibly unsafe, not for production use]

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DrahtBot removed the label DrahtBot Guix build requested on Oct 9, 2025

hebasto approved

hebasto commented at 10:32 am on October 9, 2025: member

ACK 97762b1fcf5d389b4f9c06ae46d6408fb78627b0.

maflcko commented at 10:59 am on October 9, 2025: member

Reminds me that the windows guix build is actually disabled in DrahtBot: https://github.com/maflcko/DrahtBot/blob/cd13339b9c72a12dc47931cd40e1c8872d9ac74d/guix/src/main.rs#L299, so pls ignore the result above, sry.

randomenv: Fix MinGW dllimport warning for environ #33570

Code Coverage & Benchmarks

Reviews

Guix builds (on x86_64) [untrusted test-only build, possibly unsafe, not for production use]

randomenv: Fix MinGW dllimport warning for `environ` #33570