gc.c: rename mrb_alloca() to mrb_temp_alloc() and fix memory leaks

matz · claude · matz · commit 7fe5c2e260cf · 2026-01-08T08:23:51.000+09:00
rename mrb_alloca() to mrb_temp_alloc() for clearer naming - the new name
better describes its purpose as GC-managed temporary allocation. keep
mrb_alloca() as a macro alias for backward compatibility.

apply mrb_temp_alloc() to fix potential memory leaks in:
- mruby-strftime: if mrb_str_cat() raises, allocated buffers now cleaned by GC
- mruby-io File.readlink: if mrb_str_new() raises, buffer now cleaned by GC

Co-authored-by: Claude &lt;noreply@anthropic.com&gt;
diff --git a/include/mruby.h b/include/mruby.h
@@ -1571,7 +1571,8 @@ MRB_API mrb_value mrb_fiber_alive_p(mrb_state *mrb, mrb_value fib);
 MRB_API void mrb_stack_extend(mrb_state*, mrb_int);
 
 /* temporary memory allocation, only effective while GC arena is kept */
-MRB_API void* mrb_alloca(mrb_state *mrb, size_t);
+MRB_API void* mrb_temp_alloc(mrb_state *mrb, size_t);
+#define mrb_alloca(mrb, size) mrb_temp_alloc(mrb, size) /* for compatibility */
 
 MRB_API void mrb_state_atexit(mrb_state *mrb, mrb_atexit_func func);
 
diff --git a/mrbgems/mruby-io/src/file.c b/mrbgems/mruby-io/src/file.c
@@ -885,32 +885,30 @@ mrb_file_s_chmod(mrb_state *mrb, mrb_value klass)
  *   File.symlink("testfile", "link-to-test") #=> 0
  *   File.readlink("link-to-test")          #=> "testfile"
  */
+#ifndef PATH_MAX
+#define PATH_MAX 4096
+#endif
+
 static mrb_value
 mrb_file_s_readlink(mrb_state *mrb, mrb_value klass)
 {
   const char *path;
-  size_t bufsize = 100;
 
   mrb_get_args(mrb, "z", &path);
 
   char *tmp = mrb_locale_from_utf8(path, -1);
-  char *buf = (char*)mrb_malloc(mrb, bufsize);
+  /* Use mrb_temp_alloc for exception safety - GC will clean up on exception */
+  char *buf = (char*)mrb_temp_alloc(mrb, PATH_MAX);
 
-  int64_t rc;
-  while ((rc = mrb_hal_io_readlink(mrb, tmp, buf, bufsize)) == (int64_t)bufsize) {
-    bufsize += 100;
-    buf = (char*)mrb_realloc(mrb, buf, bufsize);
-  }
+  int64_t rc = mrb_hal_io_readlink(mrb, tmp, buf, PATH_MAX);
   mrb_locale_free(tmp);
   if (rc == -1) {
-    mrb_free(mrb, buf);
     mrb_sys_fail(mrb, path);
   }
   tmp = mrb_utf8_from_locale(buf, -1);
 
   mrb_value ret = mrb_str_new(mrb, tmp, rc);
   mrb_utf8_free(tmp);
-  mrb_free(mrb, buf);
 
   return ret;
 }
diff --git a/mrbgems/mruby-strftime/src/strftime.c b/mrbgems/mruby-strftime/src/strftime.c
@@ -12,7 +12,6 @@
 #include <time.h>
 #include <string.h>
 
-#define INITIAL_BUFFER_SIZE 64
 #define MAX_BUFFER_SIZE 4096
 
 /*
@@ -60,12 +59,12 @@ mrb_time_strftime(mrb_state *mrb, mrb_value self)
     /* Process this segment (up to NUL or end of string) */
     if (segment_len > 0) {
       char *segment;
-      size_t buf_size;
       char *buf;
       size_t n;
 
       /* Create null-terminated copy of this segment */
-      segment = (char *)mrb_malloc(mrb, (size_t)segment_len + 1);
+      /* Use mrb_temp_alloc for exception safety - GC will clean up on exception */
+      segment = (char *)mrb_temp_alloc(mrb, (size_t)segment_len + 1);
       memcpy(segment, fmt_ptr, (size_t)segment_len);
       segment[segment_len] = '\0';
 
@@ -74,41 +73,21 @@ mrb_time_strftime(mrb_state *mrb, mrb_value self)
       /* Scan for %- patterns in the format string */
       for (const char *p = segment; *p != '\0'; p++) {
         if (p[0] == '%' && p[1] == '-') {
-          mrb_free(mrb, segment);
           mrb_raisef(mrb, E_ARGUMENT_ERROR,
                      "strftime format flag '%-' not supported on this platform (use '%%#' on Windows)");
         }
       }
 #endif
 
       /* Allocate buffer for formatted output */
-      buf_size = INITIAL_BUFFER_SIZE;
-      buf = (char *)mrb_malloc(mrb, buf_size);
-
-      /* Try formatting; grow buffer if needed */
-      while (1) {
-        n = strftime(buf, buf_size, segment, tm);
-
-        /*
-         * strftime returns 0 if:
-         * 1. Buffer is too small (retry with larger buffer)
-         * 2. Format produces empty result (stop retrying)
-         * We distinguish by checking buffer size limit.
-         */
-        if (n > 0 || buf_size >= MAX_BUFFER_SIZE) {
-          break;
-        }
+      /* Use mrb_temp_alloc with max size for exception safety */
+      buf = (char *)mrb_temp_alloc(mrb, MAX_BUFFER_SIZE);
 
-        /* Double buffer size and retry */
-        buf_size *= 2;
-        buf = (char *)mrb_realloc(mrb, buf, buf_size);
-      }
+      /* Try formatting with max buffer size */
+      n = strftime(buf, MAX_BUFFER_SIZE, segment, tm);
 
       /* Append formatted output to result */
       mrb_str_cat(mrb, result, buf, n);
-
-      mrb_free(mrb, buf);
-      mrb_free(mrb, segment);
     }
 
     /* If there was a NUL, append it to result and advance past it */
diff --git a/src/gc.c b/src/gc.c
@@ -266,7 +266,7 @@ mrb_free(mrb_state *mrb, void *p)
 }
 
 MRB_API void*
-mrb_alloca(mrb_state *mrb, size_t size)
+mrb_temp_alloc(mrb_state *mrb, size_t size)
 {
   struct RString *s;
   s = MRB_OBJ_ALLOC(mrb, MRB_TT_STRING, NULL);

Original file line number	Diff line number	Diff line change
`@@ -266,7 +266,7 @@ mrb_free(mrb_state mrb, void p)`
`266`	`266`	`}`
`267`	`267`
`268`	`268`	`MRB_API void*`
`269`		`-mrb_alloca(mrb_state *mrb, size_t size)`
	`269`	`+mrb_temp_alloc(mrb_state *mrb, size_t size)`
`270`	`270`	`{`
`271`	`271`	`struct RString *s;`
`272`	`272`	`s = MRB_OBJ_ALLOC(mrb, MRB_TT_STRING, NULL);`