uftrace: do not attempt to hook "backtrace"

Fixes segmentation fault on ARM devices at least.

backtrace (from execinfo.h) is not available on Android.

%ci:reset-backlog

packages/uftrace/build.sh

@@ -2,7 +2,7 @@ TERMUX_PKG_HOMEPAGE=https://uftrace.github.io/slide
 TERMUX_PKG_DESCRIPTION="Function (graph) tracer for user-space"
 TERMUX_PKG_LICENSE="GPL-2.0"
 TERMUX_PKG_VERSION=0.9.3
-TERMUX_PKG_REVISION=4
+TERMUX_PKG_REVISION=5
 TERMUX_PKG_SRCURL=https://github.com/namhyung/uftrace/archive/v${TERMUX_PKG_VERSION}.tar.gz
 TERMUX_PKG_SHA256=d801d72e3cdd83c510aeecc5160482d879498cf08fffd21e64f84151001e18ea
 TERMUX_PKG_DEPENDS="capstone, libandroid-glob, libandroid-spawn, libelf, ncurses, python2"

packages/uftrace/libmcount-wrap.c.patch

@@ -1,5 +1,47 @@
-+++ ./libmcount/wrap.c	2019-08-26 04:38:48.830364663 +0300
+diff -uNr uftrace-0.9.3/libmcount/wrap.c uftrace-0.9.3.mod/libmcount/wrap.c
-@@ -324,7 +324,8 @@
+--- uftrace-0.9.3/libmcount/wrap.c	2019-07-13 17:25:47.000000000 +0300
++++ uftrace-0.9.3.mod/libmcount/wrap.c	2019-09-03 20:46:52.430226391 +0300
+@@ -216,7 +216,6 @@
+ /*
+  * hooking functions
+  */
+-static int (*real_backtrace)(void **buffer, int sz);
+ static void (*real_cxa_throw)(void *exc, void *type, void *dest);
+ static void (*real_cxa_rethrow)(void);
+ static void * (*real_cxa_begin_catch)(void *exc);
+@@ -241,7 +240,6 @@
+ 
+ void mcount_hook_functions(void)
+ {
+-	real_backtrace		= dlsym(RTLD_NEXT, "backtrace");
+ 	real_cxa_throw		= dlsym(RTLD_NEXT, "__cxa_throw");
+ 	real_cxa_rethrow	= dlsym(RTLD_NEXT, "__cxa_rethrow");
+ 	real_cxa_begin_catch	= dlsym(RTLD_NEXT, "__cxa_begin_catch");
+@@ -258,22 +256,7 @@
+ 
+ __visible_default int backtrace(void **buffer, int sz)
+ {
+-	int ret;
+-	struct mcount_thread_data *mtdp;
+-
+-	if (unlikely(real_backtrace == NULL))
+-		mcount_hook_functions();
+-
+-	mtdp = get_thread_data();
+-	if (!check_thread_data(mtdp))
+-		mcount_rstack_restore(mtdp);
+-
+-	ret = real_backtrace(buffer, sz);
+-
+-	if (!check_thread_data(mtdp))
+-		mcount_rstack_reset(mtdp);
+-
+-	return ret;
++	return 0;
+ }
+ 
+ __visible_default void __cxa_throw(void *exception, void *type, void *dest)
+@@ -324,7 +307,8 @@
  	real_cxa_rethrow();
  }
  
@@ -9,7 +51,7 @@
  {
  	struct mcount_thread_data *mtdp;
  
-@@ -345,7 +346,7 @@
+@@ -345,7 +329,7 @@
  		mcount_rstack_restore(mtdp);
  	}