Revert "Distinguish printf-like functions that support %m from those that don't."

This reverts commit 3a60c8ff892a8242b907f44702bfd9f1ff877d45.  Buildfarm
results show that that caused a whole bunch of new warnings on platforms
where gcc believes the local printf to be non-POSIX-compliant.  This
problem outweighs the hypothetical-anyway possibility of getting warnings
for misuse of %m.  We could use gnu_printf archetype when we've substituted
src/port/snprintf.c, but that brings us right back to the problem of not
getting warnings for %m.

A possible answer is to attack it in the other direction by insisting
that %m support be included in printf's feature set, but that will take
more investigation.  In the meantime, revert the previous change, and
update the comment for PGAC_C_PRINTF_ARCHETYPE to more fully explain
what's going on.

Discussion: https://postgr.es/m/2975.1526862605@sss.pgh.pa.us

1 files changed, 13 insertions, 7 deletions

diff --git a/config/c-compiler.m4 b/config/c-compiler.m4
index dfcc1c6600..67675a31bb 100644
--- a/config/c-compiler.m4
+++ b/config/c-compiler.m4
@@ -19,12 +19,18 @@ fi])# PGAC_C_SIGNED
 
 # PGAC_C_PRINTF_ARCHETYPE
 # -----------------------
-# Set the format archetype used by gcc to check elog/ereport functions.
-# This should accept %m, whether or not the platform's printf does.
-# We use "gnu_printf" if possible, which does that, although in some cases
-# it might do more than we could wish.
+# Select the format archetype to be used by gcc to check printf-type functions.
+# We prefer "gnu_printf", which matches the features glibc supports, notably
+# %m, 'z' and 'll' width modifiers ('ll' only matters if int64 requires it),
+# and argument order control if we're doing --enable-nls.  On platforms where
+# the native printf doesn't have 'z'/'ll' or arg control, we replace it with
+# src/port/snprintf.c which does, so that the only potential mismatch here is
+# whether or not %m is supported.  We need that for elog/ereport, so we live
+# with the fact that erroneous use of %m in plain printf calls won't be
+# detected.  (It appears that many versions of gcc/clang wouldn't report it
+# even if told to check according to plain printf archetype, anyway.)
 AC_DEFUN([PGAC_PRINTF_ARCHETYPE],
-[AC_CACHE_CHECK([for printf format archetype for %m], pgac_cv_printf_archetype,
+[AC_CACHE_CHECK([for printf format archetype], pgac_cv_printf_archetype,
 [ac_save_c_werror_flag=$ac_c_werror_flag
 ac_c_werror_flag=yes
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
@@ -34,8 +40,8 @@ __attribute__((format(gnu_printf, 2, 3)));], [])],
                   [pgac_cv_printf_archetype=gnu_printf],
                   [pgac_cv_printf_archetype=printf])
 ac_c_werror_flag=$ac_save_c_werror_flag])
-AC_DEFINE_UNQUOTED([PG_PRINTF_ATTRIBUTE_M], [$pgac_cv_printf_archetype],
-                   [Define as a format archetype that accepts %m, if available, else printf.])
+AC_DEFINE_UNQUOTED([PG_PRINTF_ATTRIBUTE], [$pgac_cv_printf_archetype],
+                   [Define to gnu_printf if compiler supports it, else printf.])
 ])# PGAC_PRINTF_ARCHETYPE