Export system malloc() and free() as dlmalloc() and dlfree() so that applications can have an easier mechanism to just hook in between to the existing malloc and free, but still keep calling the original dlmalloc and dlfree.

Author: juj

system/lib/dlmalloc.c

@@ -6017,6 +6017,16 @@ int mspace_mallopt(int param_number, int value) {
 
 #endif /* MSPACES */
 
+// Export malloc and free as duplicate names dlmalloc and dlfree so that
+// applications can replace malloc and free in their code, and make those
+// replacements refer to the original dlmalloc and dlfree from this file.
+// This allows an easy mechanism for hooking into memory allocation.
+#if defined(__EMSCRIPTEN__) && !defined(USE_DL_PREFIX)
+#undef dlmalloc
+#undef dlfree
+extern __typeof(malloc) dlmalloc __attribute__((weak, alias("malloc")));
+extern __typeof(free) dlfree __attribute__((weak, alias("free")));
+#endif
 
 /* -------------------- Alternative MORECORE functions ------------------- */
 

tests/test_core.py

@@ -7178,6 +7178,9 @@ def test_brk(self):
     self.emcc_args += ['-DTEST_BRK=1']
     self.do_run(open(path_from_root('tests', 'sbrk_brk.cpp')).read(), 'OK.')
 
+  def test_wrap_malloc(self):
+    self.do_run(open(path_from_root('tests', 'wrap_malloc.cpp')).read(), 'OK.')
+
 # Generate tests for everything
 def make_run(fullname, name=-1, compiler=-1, embetter=0, quantum_size=0,
     typed_arrays=0, emcc_args=None, env=None):

tests/wrap_malloc.cpp

@@ -0,0 +1,38 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+int totalAllocated = 0;
+int totalFreed = 0;
+
+extern "C"
+{
+
+extern void* dlmalloc(size_t bytes);
+extern void dlfree(void* mem);
+
+void * __attribute__((noinline)) malloc(size_t size)
+{
+	++totalAllocated;
+	void *ptr = dlmalloc(size);
+	printf("Allocated %u bytes, got %p. %d pointers allocated total.\n", size, ptr, totalAllocated);
+	return ptr;
+}
+
+void __attribute__((noinline)) free(void *ptr)
+{
+	++totalFreed;
+	dlfree(ptr);
+	printf("Freed ptr %p, %d pointers freed total.\n", ptr, totalFreed);
+}
+
+}
+
+int main()
+{
+	for(int i = 0; i < 20; ++i)
+	{
+		void *ptr = malloc(1024 * 1024);
+		free(ptr);
+	}
+	printf("OK.\n");
+}