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 a13b47a5, 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

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
 
 

configure

@@ -13362,8 +13362,8 @@ _ACEOF
     ;;
 esac
 
-{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for printf format archetype" >&5
-$as_echo_n "checking for printf format archetype... " >&6; }
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for printf format archetype for %m" >&5
+$as_echo_n "checking for printf format archetype for %m... " >&6; }
 if ${pgac_cv_printf_archetype+:} false; then :
   $as_echo_n "(cached) " >&6
 else
@@ -13394,7 +13394,7 @@ fi
 $as_echo "$pgac_cv_printf_archetype" >&6; }
 
 cat >>confdefs.h <<_ACEOF
-#define PG_PRINTF_ATTRIBUTE $pgac_cv_printf_archetype
+#define PG_PRINTF_ATTRIBUTE_M $pgac_cv_printf_archetype
 _ACEOF
 
 

src/include/c.h

@@ -126,10 +126,14 @@
 /* GCC and XLC support format attributes */
 #if defined(__GNUC__) || defined(__IBMC__)
 #define pg_attribute_format_arg(a) __attribute__((format_arg(a)))
-#define pg_attribute_printf(f,a) __attribute__((format(PG_PRINTF_ATTRIBUTE, f, a)))
+/* Use for functions wrapping stdio's printf, which often doesn't take %m: */
+#define pg_attribute_printf(f,a) __attribute__((format(printf, f, a)))
+/* Use for elog/ereport, which implement %m for themselves: */
+#define pg_attribute_printf_m(f,a) __attribute__((format(PG_PRINTF_ATTRIBUTE_M, f, a)))
 #else
 #define pg_attribute_format_arg(a)
 #define pg_attribute_printf(f,a)
+#define pg_attribute_printf_m(f,a)
 #endif
 
 /* GCC, Sunpro and XLC support aligned, packed and noreturn */

src/include/pg_config.h.in

@@ -809,8 +809,8 @@
 /* PostgreSQL major version as a string */
 #undef PG_MAJORVERSION
 
-/* Define to gnu_printf if compiler supports it, else printf. */
-#undef PG_PRINTF_ATTRIBUTE
+/* Define as a format archetype that accepts %m, if available, else printf. */
+#undef PG_PRINTF_ATTRIBUTE_M
 
 /* PostgreSQL version as a string */
 #undef PG_VERSION

src/include/utils/elog.h

@@ -133,25 +133,25 @@ extern int	errcode(int sqlerrcode);
 extern int	errcode_for_file_access(void);
 extern int	errcode_for_socket_access(void);
 
-extern int	errmsg(const char *fmt,...) pg_attribute_printf(1, 2);
-extern int	errmsg_internal(const char *fmt,...) pg_attribute_printf(1, 2);
+extern int	errmsg(const char *fmt,...) pg_attribute_printf_m(1, 2);
+extern int	errmsg_internal(const char *fmt,...) pg_attribute_printf_m(1, 2);
 
 extern int errmsg_plural(const char *fmt_singular, const char *fmt_plural,
-			  unsigned long n,...) pg_attribute_printf(1, 4) pg_attribute_printf(2, 4);
+			  unsigned long n,...) pg_attribute_printf_m(1, 4) pg_attribute_printf_m(2, 4);
 
-extern int	errdetail(const char *fmt,...) pg_attribute_printf(1, 2);
-extern int	errdetail_internal(const char *fmt,...) pg_attribute_printf(1, 2);
+extern int	errdetail(const char *fmt,...) pg_attribute_printf_m(1, 2);
+extern int	errdetail_internal(const char *fmt,...) pg_attribute_printf_m(1, 2);
 
-extern int	errdetail_log(const char *fmt,...) pg_attribute_printf(1, 2);
+extern int	errdetail_log(const char *fmt,...) pg_attribute_printf_m(1, 2);
 
 extern int errdetail_log_plural(const char *fmt_singular,
 					 const char *fmt_plural,
-					 unsigned long n,...) pg_attribute_printf(1, 4) pg_attribute_printf(2, 4);
+					 unsigned long n,...) pg_attribute_printf_m(1, 4) pg_attribute_printf_m(2, 4);
 
 extern int errdetail_plural(const char *fmt_singular, const char *fmt_plural,
-				 unsigned long n,...) pg_attribute_printf(1, 4) pg_attribute_printf(2, 4);
+				 unsigned long n,...) pg_attribute_printf_m(1, 4) pg_attribute_printf_m(2, 4);
 
-extern int	errhint(const char *fmt,...) pg_attribute_printf(1, 2);
+extern int	errhint(const char *fmt,...) pg_attribute_printf_m(1, 2);
 
 /*
  * errcontext() is typically called in error context callback functions, not
@@ -165,7 +165,7 @@ extern int	errhint(const char *fmt,...) pg_attribute_printf(1, 2);
 
 extern int	set_errcontext_domain(const char *domain);
 
-extern int	errcontext_msg(const char *fmt,...) pg_attribute_printf(1, 2);
+extern int	errcontext_msg(const char *fmt,...) pg_attribute_printf_m(1, 2);
 
 extern int	errhidestmt(bool hide_stmt);
 extern int	errhidecontext(bool hide_ctx);
@@ -222,13 +222,13 @@ extern int	getinternalerrposition(void);
 #endif							/* HAVE__VA_ARGS */
 
 extern void elog_start(const char *filename, int lineno, const char *funcname);
-extern void elog_finish(int elevel, const char *fmt,...) pg_attribute_printf(2, 3);
+extern void elog_finish(int elevel, const char *fmt,...) pg_attribute_printf_m(2, 3);
 
 
 /* Support for constructing error strings separately from ereport() calls */
 
 extern void pre_format_elog_string(int errnumber, const char *domain);
-extern char *format_elog_string(const char *fmt,...) pg_attribute_printf(1, 2);
+extern char *format_elog_string(const char *fmt,...) pg_attribute_printf_m(1, 2);
 
 
 /* Support for attaching context information to error reports */
@@ -407,9 +407,9 @@ extern void set_syslog_parameters(const char *ident, int facility);
 #endif
 
 /*
- * Write errors to stderr (or by equal means when stderr is
- * not available). Used before ereport/elog can be used
- * safely (memory context, GUC load etc)
+ * Write errors to stderr (or by comparable means when stderr is not
+ * available).  Used before ereport/elog can be used safely (memory context,
+ * GUC load etc).  Note that this does *not* accept "%m".
  */
 extern void write_stderr(const char *fmt,...) pg_attribute_printf(1, 2);