Support "j" length modifier in snprintf.c.

tglsfdc · tglsfdc · commit f8715ec86608 · 2025-12-09T11:43:25.000-05:00
POSIX has for a long time defined the "j" length modifier for printf conversions as meaning the size of intmax_t or uintmax_t. We got away without supporting that so far, because we were not using intmax_t anywhere. However, commit e6be843 re-introduced upstream's use of intmax_t and PRIdMAX into zic.c. It emerges that on some platforms (at least FreeBSD and macOS), <inttypes.h> defines PRIdMAX as "jd", so that snprintf.c falls over if that is used. (We hadn't noticed yet because it would only be apparent if bad data is fed to zic, resulting in an error report, and even then the only visible symptom is a missing line number in the error message.) We could revert that decision from our copy of zic.c, but on the whole it seems better to update snprintf.c to support this standard modifier. There might well be extensions, now or in future, that expect it to work. I did this in the lazy man's way of translating "j" to either "l" or "ll" depending on a compile-time sizeof() check, just as was done long ago to support "z" for size_t. One could imagine promoting intmax_t to have full support in snprintf.c, for example converting fmtint()'s value argument and internal arithmetic to use [u]intmax_t not [unsigned] long long. But that'd be more work and I'm hesitant to do it anyway: if there are any platforms out there where intmax_t is actually wider than "long long", this would doubtless result in a noticeable speed penalty to snprintf(). Let's not go there until we have positive evidence that there's a reason to, and some way to measure what size of penalty we're taking. Author: Tom Lane <tgl@sss.pgh.pa.us> Discussion: https://postgr.es/m/3210703.1765236740@sss.pgh.pa.us
diff --git a/configure b/configure
@@ -16853,6 +16853,39 @@ cat >>confdefs.h <<_ACEOF
 _ACEOF
 
 
+# The cast to long int works around a bug in the HP C Compiler
+# version HP92453-01 B.11.11.23709.GP, which incorrectly rejects
+# declarations like `int a3[[(sizeof (unsigned char)) >= 0]];'.
+# This bug is HP SR number 8606223364.
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking size of intmax_t" >&5
+$as_echo_n "checking size of intmax_t... " >&6; }
+if ${ac_cv_sizeof_intmax_t+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  if ac_fn_c_compute_int "$LINENO" "(long int) (sizeof (intmax_t))" "ac_cv_sizeof_intmax_t"        "$ac_includes_default"; then :
+
+else
+  if test "$ac_cv_type_intmax_t" = yes; then
+     { { $as_echo "$as_me:${as_lineno-$LINENO}: error: in \`$ac_pwd':" >&5
+$as_echo "$as_me: error: in \`$ac_pwd':" >&2;}
+as_fn_error 77 "cannot compute sizeof (intmax_t)
+See \`config.log' for more details" "$LINENO" 5; }
+   else
+     ac_cv_sizeof_intmax_t=0
+   fi
+fi
+
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_sizeof_intmax_t" >&5
+$as_echo "$ac_cv_sizeof_intmax_t" >&6; }
+
+
+
+cat >>confdefs.h <<_ACEOF
+#define SIZEOF_INTMAX_T $ac_cv_sizeof_intmax_t
+_ACEOF
+
+
 
 # Determine memory alignment requirements for the basic C data types.
 
diff --git a/configure.ac b/configure.ac
@@ -1983,6 +1983,7 @@ AC_CHECK_SIZEOF([void *])
 AC_CHECK_SIZEOF([size_t])
 AC_CHECK_SIZEOF([long])
 AC_CHECK_SIZEOF([long long])
+AC_CHECK_SIZEOF([intmax_t])
 
 # Determine memory alignment requirements for the basic C data types.
 
diff --git a/meson.build b/meson.build
@@ -1776,6 +1776,8 @@ cdata.set('SIZEOF_LONG', cc.sizeof('long', args: test_c_args))
 cdata.set('SIZEOF_LONG_LONG', cc.sizeof('long long', args: test_c_args))
 cdata.set('SIZEOF_VOID_P', cc.sizeof('void *', args: test_c_args))
 cdata.set('SIZEOF_SIZE_T', cc.sizeof('size_t', args: test_c_args))
+cdata.set('SIZEOF_INTMAX_T', cc.sizeof('intmax_t', args: test_c_args,
+                                       prefix: '#include <stdint.h>'))
 
 
 # Check if __int128 is a working 128 bit integer type, and if so
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
@@ -645,6 +645,9 @@
    RELSEG_SIZE requires an initdb. */
 #undef RELSEG_SIZE
 
+/* The size of `intmax_t', as computed by sizeof. */
+#undef SIZEOF_INTMAX_T
+
 /* The size of `long', as computed by sizeof. */
 #undef SIZEOF_LONG
 
diff --git a/src/port/snprintf.c b/src/port/snprintf.c
@@ -563,6 +563,15 @@ dopr(PrintfTarget *target, const char *format, va_list args)
 				else
 					longflag = 1;
 				goto nextch2;
+			case 'j':
+#if SIZEOF_INTMAX_T == SIZEOF_LONG
+				longflag = 1;
+#elif SIZEOF_INTMAX_T == SIZEOF_LONG_LONG
+				longlongflag = 1;
+#else
+#error "cannot find integer type of the same size as intmax_t"
+#endif
+				goto nextch2;
 			case 'z':
 #if SIZEOF_SIZE_T == SIZEOF_LONG
 				longflag = 1;
@@ -826,6 +835,15 @@ find_arguments(const char *format, va_list args,
 				else
 					longflag = 1;
 				goto nextch1;
+			case 'j':
+#if SIZEOF_INTMAX_T == SIZEOF_LONG
+				longflag = 1;
+#elif SIZEOF_INTMAX_T == SIZEOF_LONG_LONG
+				longlongflag = 1;
+#else
+#error "cannot find integer type of the same size as intmax_t"
+#endif
+				goto nextch1;
 			case 'z':
 #if SIZEOF_SIZE_T == SIZEOF_LONG
 				longflag = 1;
