Add hooking functionality

This allows us to hook chosen functions and do interesting things there (in
particular: reentrancy checking).

src/hooks.c

@@ -0,0 +1,12 @@
+#include "jemalloc/internal/jemalloc_internal.h"
+
+/*
+ * The hooks are a little bit screwy -- they're not genuinely exported in the
+ * sense that we want them available to end-users, but we do want them visible
+ * from outside the generated library, so that we can use them in test code.
+ */
+JEMALLOC_EXPORT
+void (*hooks_arena_new_hook)() = NULL;
+
+JEMALLOC_EXPORT
+void (*hooks_libc_hook)() = NULL;

src/prof.c

@@ -8,7 +8,14 @@
 #endif
 
 #ifdef JEMALLOC_PROF_LIBGCC
+/*
+ * We have a circular dependency -- jemalloc_internal.h tells us if we should
+ * use libgcc's unwinding functionality, but after we've included that, we've
+ * already hooked _Unwind_Backtrace.  We'll temporarily disable hooking.
+ */
+#undef _Unwind_Backtrace
 #include <unwind.h>
+#define _Unwind_Backtrace JEMALLOC_HOOK(_Unwind_Backtrace, hooks_libc_hook)
 #endif
 
 /******************************************************************************/

src/tsd.c

@@ -149,6 +149,15 @@ _tls_callback(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved) {
 	return true;
 }
 
+/*
+ * We need to be able to say "read" here (in the "pragma section"), but have
+ * hooked "read". We won't read for the rest of the file, so we can get away
+ * with unhooking.
+ */
+#ifdef read
+#  undef read
+#endif
+
 #ifdef _MSC_VER
 #  ifdef _M_IX86
 #    pragma comment(linker, "/INCLUDE:__tls_used")