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

3 files changed, 22 insertions, 18 deletions

diff --git a/src/include/c.h b/src/include/c.h
index 1e50103095b..0a4757e29fd 100644
--- a/src/include/c.h
+++ b/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 */
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index b7e469670f4..05775a3405f 100644
--- a/src/include/pg_config.h.in
+++ b/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
diff --git a/src/include/utils/elog.h b/src/include/utils/elog.h
index 7a9ba7f2fff..4f4091d8cc8 100644
--- a/src/include/utils/elog.h
+++ b/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);