Fix "inconsistent DLL linkage" warning on Windows MSVC

This warning was disabled in meson.build (warning 4273).  If you
enable it, it looks like this:

../src/backend/utils/misc/ps_status.c(27): warning C4273: '__p__environ': inconsistent dll linkage
C:\Program Files (x86)\Windows Kits\10\include\10.0.22621.0\ucrt\stdlib.h(1158): note: see previous definition of '__p__environ'

The declaration in ps_status.c was:

    #if !defined(WIN32) || defined(_MSC_VER)
    extern char **environ;
    #endif

The declaration in the OS header file is:

    _DCRTIMP char***    __cdecl __p__environ (void);
    #define _environ  (*__p__environ())

So it is evident that this could be problematic.

The old declaration was required by the old MSVCRT library, but we
don't support that anymore with MSVC.

To fix, disable the re-declaration in ps_status.c, and also in some
other places that use the same code pattern but didn't trigger the
warning.

Then we can also re-enable the warning (delete the disablement in
meson.build).

Reviewed-by: Bryan Green <dbryan.green@gmail.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://www.postgresql.org/message-id/flat/bf060644-47ff-441b-97cf-c685d0827757@eisentraut.org

diff --git a/meson.build b/meson.build
index 00c46d400714412d96e028cbf67bb3ca34746b16..24aeffe929f055d18bdb14c94c1c191561480d5a 100644 (file)
--- a/meson.build
+++ b/meson.build
@@ -2150,7 +2150,6 @@ if cc.get_id() == 'msvc'
     # Warnings to disable:
     # from /W1:
     '/wd4090', # different 'modifier' qualifiers
-    '/wd4273', # inconsistent DLL linkage
     # from /W2:
     '/wd4244', # conversion from 'type1' to 'type2', possible loss of data
     # from /W3:

diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 00de559ba8f41f489efabf93902290e6e6d3a78d..7c064cf9fbb288180380521dee24f5c03db439c4 100644 (file)
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -880,7 +880,7 @@ PostmasterMain(int argc, char *argv[])
        /* For debugging: display postmaster environment */
        if (message_level_is_interesting(DEBUG3))
        {
-#if !defined(WIN32) || defined(_MSC_VER)
+#if !defined(WIN32)
                extern char **environ;
 #endif
                char      **p;

diff --git a/src/backend/utils/misc/ps_status.c b/src/backend/utils/misc/ps_status.c
index 4df25944deb33c4983942eea489bd18099c6e988..8709c4f51250838c1cca870d6b384d595d6c60f8 100644 (file)
--- a/src/backend/utils/misc/ps_status.c
+++ b/src/backend/utils/misc/ps_status.c
@@ -23,7 +23,7 @@
 #include "utils/guc.h"
 #include "utils/ps_status.h"
 
-#if !defined(WIN32) || defined(_MSC_VER)
+#if !defined(WIN32)
 extern char **environ;
 #endif
 

diff --git a/src/test/regress/regress.c b/src/test/regress/regress.c
index 465ac148ac9f74d5ac310910f9f54e92b54a0037..a2db6080876e1789c40baec9ddb2366932a333bb 100644 (file)
--- a/src/test/regress/regress.c
+++ b/src/test/regress/regress.c
@@ -432,7 +432,7 @@ PG_FUNCTION_INFO_V1(get_environ);
 Datum
 get_environ(PG_FUNCTION_ARGS)
 {
-#if !defined(WIN32) || defined(_MSC_VER)
+#if !defined(WIN32)
        extern char **environ;
 #endif
        int                     nvals = 0;