Support printf %n directive

libc/fmt/internal.h

@@ -47,6 +47,6 @@
 
 int __vcscanf(int (*)(void *), int (*)(int, void *), void *, const char *,
               va_list);
-int __fmt(void *, void *, const char *, va_list);
+int __fmt(void *, void *, const char *, va_list, int *);
 
 #endif /* COSMOPOLITAN_LIBC_FMT_STRTOL_H_ */

libc/stdio/fmt.c

@@ -43,6 +43,7 @@
 #include "libc/errno.h"
 #include "libc/fmt/conv.h"
 #include "libc/fmt/divmod10.internal.h"
+#include "libc/fmt/internal.h"
 #include "libc/fmt/itoa.h"
 #include "libc/intrin/bsr.h"
 #include "libc/intrin/nomultics.h"
@@ -820,7 +821,7 @@ static int __fmt_noop(const char *, void *, size_t) {
  * @asyncsignalsafe if floating point isn't used
  * @vforksafe if floating point isn't used
  */
-int __fmt(void *fn, void *arg, const char *format, va_list va) {
+int __fmt(void *fn, void *arg, const char *format, va_list va, int *wrote) {
   long ld;
   void *p;
   double x;
@@ -1121,7 +1122,7 @@ int __fmt(void *fn, void *arg, const char *format, va_list va) {
         }
         break;
       case 'n':
-        __FMT_PUT('\n');
+        *va_arg(va, int *) = *wrote;
         break;
 
       case 'F':

libc/stdio/vdprintf.c

@@ -63,7 +63,7 @@ int vdprintf(int fd, const char *fmt, va_list va) {
   t.n = 0;
   t.t = 0;
   t.fd = fd;
-  if (__fmt(vdprintf_putc, &t, fmt, va) == -1)
+  if (__fmt(vdprintf_putc, &t, fmt, va, &t.t) == -1)
     return -1;
   if (t.n) {
     iov[0].iov_base = t.b;

libc/stdio/vfprintf_unlocked.c

@@ -87,7 +87,7 @@ int vfprintf_unlocked(FILE *f, const char *fmt, va_list va) {
   st.f = f;
   st.n = 0;
   st.b.n = 0;
-  if ((rc = __fmt(out, &st, fmt, va)) != -1) {
+  if ((rc = __fmt(out, &st, fmt, va, &st.n)) != -1) {
     if (!st.b.n) {
       rc = st.n;
     } else if (fwrite_unlocked(st.b.p, 1, st.b.n, st.f)) {

libc/stdio/vsnprintf.c

@@ -26,8 +26,8 @@
 
 struct SprintfStr {
   char *p;
-  size_t i;
-  size_t n;
+  int i;
+  int n;
 };
 
 static int vsnprintfputchar(const char *s, struct SprintfStr *t, size_t n) {
@@ -58,7 +58,7 @@ static int vsnprintfputchar(const char *s, struct SprintfStr *t, size_t n) {
  */
 int vsnprintf(char *buf, size_t size, const char *fmt, va_list va) {
   struct SprintfStr str = {buf, 0, size};
-  int rc = __fmt(vsnprintfputchar, &str, fmt, va);
+  int rc = __fmt(vsnprintfputchar, &str, fmt, va, &str.i);
   if (rc < 0)
     return rc;
   if (str.n)

test/libc/stdio/fmt_test.c

@@ -20,6 +20,7 @@
 #include "libc/log/log.h"
 #include "libc/math.h"
 #include "libc/mem/gc.h"
+#include "libc/stdio/stdio.h"
 #include "libc/str/str.h"
 #include "libc/testlib/testlib.h"
 #include "libc/x/xasprintf.h"
@@ -431,3 +432,10 @@ TEST(fmt, regress) {
       "User-Agent: hurl/1.o (https://github.com/jart/cosmopolitan)\r\n",
       buf);
 }
+
+TEST(fmt, n) {
+  int n;
+  char buf[8];
+  snprintf(buf, 8, ".%c%c.%n", 0, 1, &n);
+  ASSERT_EQ(4, n);
+}

tool/cosmocc/bin/cosmocc

@@ -165,6 +165,8 @@ for x; do
   elif [ x"$x" = x"-moptlinux" ]; then
     MODE=optlinux
     continue
+  elif [ x"$x" = x"-m64" ]; then
+    continue
   elif [ x"$x" = x"-fomit-frame-pointer" ]; then
     # Quoth Apple: "The frame pointer register must always address a
     # valid frame record. Some functions — such as leaf functions or

tool/cosmocc/bin/cosmocross

@@ -172,6 +172,8 @@ for x; do
     continue
   elif [ x"$x" = x"-moptlinux" ]; then
     continue
+  elif [ x"$x" = x"-m64" ]; then
+    continue
   elif [ x"$x" != x"${x#-o}" ]; then
     OUTPUT=${x#-o}
   elif [ x"$x" = x"-fpic" ]; then