util/u_printf: properly handle %%

Cc: mesa-stable
Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29776>

src/util/tests/u_printf_test.cpp

@@ -217,5 +217,5 @@ TEST_F(u_printf_test, util_printf_mixed_multiple)
    add_arg<float>(3.0);
    add_arg<float, 4>(floats);
 
-   EXPECT_EQ(parse(), "ABCED\n-5 6\n%%%%mesa 10 3.000000 1.0,2.0,3.0,4.0 ");
+   EXPECT_EQ(parse(), "ABCED\n-5 6\n%%mesa 10 3.000000 1.0,2.0,3.0,4.0 ");
 }

src/util/u_printf.c

@@ -99,6 +99,42 @@ size_t u_printf_length(const char *fmt, va_list untouched_args)
    return size;
 }
 
+/**
+ * Used to print plain format strings without arguments as some post-processing
+ * will be required:
+ *  - %% needs to be printed as %
+ */
+static void
+u_printf_plain_sized(FILE *out, const char* format, size_t len)
+{
+   bool found = false;
+   size_t last = 0;
+
+   for (size_t i = 0; i < len; i++) {
+      if (!found && format[i] == '%') {
+         found = true;
+      } else if (found && format[i] == '%') {
+         /* print one character less so we only print a single % */
+         fwrite(format + last, i - last - 1, 1, out);
+
+         last = i;
+         found = false;
+      } else {
+         /* We should never end up here with an actual format token */
+         assert(!found);
+         found = false;
+      }
+   }
+
+   fwrite(format + last, len - last, 1, out);
+}
+
+static void
+u_printf_plain(FILE *out, const char* format)
+{
+   u_printf_plain_sized(out, format, strlen(format));
+}
+
 static void
 u_printf_impl(FILE *out, const char *buffer, size_t buffer_size,
               const u_printf_info *info,
@@ -122,7 +158,7 @@ u_printf_impl(FILE *out, const char *buffer, size_t buffer_size,
       buf_pos += sizeof(fmt_idx);
 
       if (!fmt->num_args) {
-         fprintf(out, "%s", format);
+         u_printf_plain(out, format);
          continue;
       }
 
@@ -131,7 +167,7 @@ u_printf_impl(FILE *out, const char *buffer, size_t buffer_size,
          size_t spec_pos = util_printf_next_spec_pos(format, 0);
 
          if (spec_pos == -1) {
-            fprintf(out, "%s", format);
+            u_printf_plain(out, format);
             continue;
          }
 
@@ -140,13 +176,13 @@ u_printf_impl(FILE *out, const char *buffer, size_t buffer_size,
 
          /* print the part before the format token */
          if (token != format)
-            fwrite(format, token - format, 1, out);
+            u_printf_plain_sized(out, format, token - format);
 
          char *print_str = strndup(token, next_format - token);
          /* rebase spec_pos so we can use it with print_str */
          spec_pos += format - token;
 
-         /* print the formated part */
+         /* print the formatted part */
          if (print_str[spec_pos] == 's') {
             uint64_t idx;
             memcpy(&idx, &buffer[buf_pos], 8);
@@ -233,7 +269,7 @@ u_printf_impl(FILE *out, const char *buffer, size_t buffer_size,
       }
 
       /* print remaining */
-      fprintf(out, "%s", format);
+      u_printf_plain(out, format);
    }
 }