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

The elog/ereport family of functions certainly support the %m format spec,
because they implement it "by hand".  But elsewhere we have printf wrappers
that might or might not allow it depending on whether the platform's printf
does.  (Most non-glibc versions don't, and notably, src/port/snprintf.c
doesn't.)  Hence, rather than using the gnu_printf format archetype
interchangeably for all these functions, use it only for elog/ereport.
This will allow us to get compiler warnings for mistakes like the ones
fixed in commit a13b47a59, at least on platforms where printf doesn't
take %m and gcc is correctly configured to know it.  (Unfortunately,
that won't happen on Linux, nor on macOS according to my testing.
It remains to be seen what the buildfarm's gcc-on-Windows animals will
think of this, but we may well have to rely on less-popular platforms
to warn us about unportable code of this kind.)

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

1 files changed, 7 insertions, 7 deletions

diff --git a/config/c-compiler.m4 b/config/c-compiler.m4
index 9731a517dee..dfcc1c66006 100644
--- a/config/c-compiler.m4
+++ b/config/c-compiler.m4
@@ -19,12 +19,12 @@ fi])# PGAC_C_SIGNED
 
 # PGAC_C_PRINTF_ARCHETYPE
 # -----------------------
-# Set the format archetype used by gcc to check printf type functions.  We
-# prefer "gnu_printf", which includes what glibc uses, such as %m for error
-# strings and %lld for 64 bit long longs.  GCC 4.4 introduced it.  It makes a
-# dramatic difference on Windows.
+# 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.
 AC_DEFUN([PGAC_PRINTF_ARCHETYPE],
-[AC_CACHE_CHECK([for printf format archetype], pgac_cv_printf_archetype,
+[AC_CACHE_CHECK([for printf format archetype for %m], pgac_cv_printf_archetype,
 [ac_save_c_werror_flag=$ac_c_werror_flag
 ac_c_werror_flag=yes
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
@@ -34,8 +34,8 @@ __attribute__((format(gnu_printf, 2, 3)));], [])],
                   [pgac_cv_printf_archetype=gnu_printf],
                   [pgac_cv_printf_archetype=printf])
 ac_c_werror_flag=$ac_save_c_werror_flag])
-AC_DEFINE_UNQUOTED([PG_PRINTF_ATTRIBUTE], [$pgac_cv_printf_archetype],
-                   [Define to gnu_printf if compiler supports it, else printf.])
+AC_DEFINE_UNQUOTED([PG_PRINTF_ATTRIBUTE_M], [$pgac_cv_printf_archetype],
+                   [Define as a format archetype that accepts %m, if available, else printf.])
 ])# PGAC_PRINTF_ARCHETYPE