Fix bad errno usage

Triggered by PostgreSQL a2a8acd152:
[...]
    This patch adds a hack to cause an (admittedly obscure) compiler error
    for such unsafe usages.  With the current code, the error will only be seen
    on Linux, macOS, and FreeBSD, but that should certainly be enough to catch
    mistakes in the buildfarm if they somehow get missed earlier.
[...]

diff --git a/pgfincore.c b/pgfincore.c
index b73d66bb2c2070270c777a49157602230e4f3bca..5658e2d9826f8cb0ea16eedf47d9447fceef40e4 100644 (file)
--- a/pgfincore.c
+++ b/pgfincore.c
@@ -815,9 +815,10 @@ pgfincore_file(char *filename, pgfincoreStruct *pgfncr)
                pa = mmap(NULL, st.st_size, PROT_NONE, MAP_SHARED, fd, 0);
                if (pa == MAP_FAILED)
                {
+                       int     save_errno = errno;
                        FreeFile(fp);
                        elog(ERROR, "Can not mmap object file : %s, errno = %i,%s\nThis error can happen if there is not enought space in memory to do the projection. Please mail cedric@villemain.org with '[pgfincore] ENOMEM' as subject.",
-                            filename, errno, strerror(errno));
+                            filename, save_errno, strerror(save_errno));
                        return 3;
                }
 #endif
@@ -839,15 +840,17 @@ pgfincore_file(char *filename, pgfincoreStruct *pgfncr)
                /* Affect vec with mincore */
                if (mincore(pa, st.st_size, vec) != 0)
                {
+                       int save_errno = errno;
                        munmap(pa, st.st_size);
                        elog(ERROR, "mincore(%p, %lld, %p): %s\n",
-                            pa, (long long int)st.st_size, vec, strerror(errno));
+                            pa, (long long int)st.st_size, vec, strerror(save_errno));
 #else
                /* Affect vec with fincore */
                if (fincore(fd, 0, st.st_size, vec) != 0)
                {
+                       int save_errno = errno;
                        elog(ERROR, "fincore(%u, 0, %lld, %p): %s\n",
-                            fd, (long long int)st.st_size, vec, strerror(errno));
+                            fd, (long long int)st.st_size, vec, strerror(save_errno));
 #endif
                        free(vec);
                        FreeFile(fp);