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.

In the mingw-w64 headers (used by llvm-mingw), environ is defined as a macro which expands through _environ to (* __p__environ()), a call to a dllimport function, causing the same inconsistent linkage warning as MSVC.

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

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]

File	commit b510893d00760083ac36948747aa6ebd84656192(master)	commit 883c8fecd5e61b32cbcba08dff4f9f876dae3be0(pull/33570/merge)
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*-arm64-apple-darwin-codesigning.tar.gz	`82cb6250417e717c...`	`7de7cc4af586b871...`
*-arm64-apple-darwin-unsigned.tar.gz	`8fc23c4c3a991331...`	`e3d67510950c2c81...`
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guix_build.log.diff		`225bb976da2b3471...`

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.

fanquake commented at 10:58 am on October 14, 2025: member

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

You should update the commit message to match.

llvm-mingw also defines environ as a macro

Can you be more clear with this explanation. llvm-mingw looks like a collection of scripts that download and build LLVM and the mingw-w64 headers. I don’t think it defines anything environ related?

randomenv: Fix MinGW dllimport warning for `environ`

Extends 7703884 to guard environ declaration on all Windows builds, not just MSVC.
In the mingw-w64 headers (used by llvm-mingw), environ is defined as a macro which expands through _environ to (* __p__environ()), a call to a dllimport function, causing the same inconsistent linkage warning as MSVC.

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).

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

9610b0d1e2

l0rinc force-pushed on Oct 14, 2025

l0rinc commented at 2:26 pm on October 14, 2025: contributor

My understanding is that https://github.com/msys2-contrib/mingw-w64/blob/cdb052f1d4056cd510cb83197b55868427b87476/mingw-w64-headers/crt/stdlib.h#L704 expands environ to _environ, and in https://github.com/msys2-contrib/mingw-w64/blob/cdb052f1d4056cd510cb83197b55868427b87476/mingw-w64-headers/crt/stdlib.h#L262-L264, _environ is further defined as a macro expanding to (* __p__environ()) (similar problem described in https://github.com/msys2/MINGW-packages/issues/13925#issuecomment-1312820489)

Updated the commit message and PR description.

hebasto approved

hebasto commented at 4:58 pm on October 16, 2025: member

re-ACK 9610b0d1e28aeda02a2ddcf1f0591ae577c3e88e.

hebasto commented at 5:03 pm on October 16, 2025: member

We use mingw-w64 in the CI & Guix build, and it doesn’t produce this warning.

GCC has no such a diagnostic: https://gcc.gnu.org/onlinedocs/gcc/Option-Summary.html.

Clang does: https://clang.llvm.org/docs/DiagnosticsReference.html#winconsistent-dllimport.

hebasto commented at 8:41 am on October 22, 2025: member

Friendly ping people who reviewed the previous change: @sipa @sipsorcery @theuni

sipa commented at 8:44 am on October 22, 2025: member

utACK 9610b0d1e28aeda02a2ddcf1f0591ae577c3e88e if this makes the compilers happy

laanwj commented at 9:20 am on October 22, 2025: member

After discussion i’m convinced that this is the right solution. According to man pages, on POSIX (non-windows) platforms, including MacOS, you are supposed to define this variable yourself. So it can’t be removed entirely.

On Windows (irrespective of compiler or toolchain) it’s provided by the headers, and defined in a different way, so if we want to use environ therel, we shouldn’t define it ourselves.

Note that it’s deprecated though:

The _environ variable is a pointer to an array of pointers to the multibyte-character strings that constitute the process environment. This global variable has been deprecated for the more secure functional versions getenv_s, _wgetenv_s and _putenv_s, _wputenv_s, which should be used in place of the global variable. _environ is declared in Stdlib.h.

Anyhow, this is the best way to fix it while keeping the functionality as-is.

Code review ACK 9610b0d1e28aeda02a2ddcf1f0591ae577c3e88e

hebasto approved

hebasto commented at 9:50 am on October 22, 2025: member

My Guix build:

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13372aedd6ed25924fc6e22596114ad8d9a994fb4c1342e1308b4fdbb7a38bdf7  guix-build-9610b0d1e28a/output/x86_64-w64-mingw32/SHA256SUMS.part
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3fd160165f6e496f0f498b56a467dea67af2c4f341326ea56e5232133af6df7c5  guix-build-9610b0d1e28a/output/x86_64-w64-mingw32/bitcoin-9610b0d1e28a-win64-debug.zip
4220f4dbaf25707986ca0320fa33711383d89ea1a56889f41dc5efa634c348072  guix-build-9610b0d1e28a/output/x86_64-w64-mingw32/bitcoin-9610b0d1e28a-win64-setup-unsigned.exe
56696f40cdb46fb4e6f67988cd6fd810133b3b1efe99c5f92980f8b22461d6c7a  guix-build-9610b0d1e28a/output/x86_64-w64-mingw32/bitcoin-9610b0d1e28a-win64-unsigned.zip

bitcoind.exe from bitcoin-9610b0d1e28a-win64-unsigned.zip has been tested on Windows 11.

hebasto merged this on Oct 22, 2025

hebasto closed this on Oct 22, 2025

l0rinc deleted the branch on Oct 22, 2025

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