Debugging

Enabling debugging features

Some nfc-tools project have debugging features that can be turned on at the ./configure stage, usualy with a --enable-debug flag:

./configure --enable-debug

Compiling with debugging symbols

Debugging the nfc-tools is easier with debugging symbols (with gcc, compile with the -g flag), but compiler optimisations may make debugging harder than necessary, so turning off optimizations is always a good idea (gcc’s -O0 flag). You may also consider increasing the warning level if you tweak the code (gcc’s -Wall and -Wextra flags). All these flags can be combined when passed to the configure script:

./configure CFLAGS="-Wall -Wextra -Werror -O0 -g"

Debugging from the build directory

The autotools usualy generate wrapper scripts for built programs. As an example, after building libfreefare, examples/mifare-desfire-info is a shell script that runs the actual program (examples/.libs/mifare-desfire-info) in an environment where it can be linked to the libfreefare/.libs/libfreefare.so.0 library.

% ldd examples/mifare-desfire-info
ldd: examples/mifare-desfire-info: not a dynamic executable
% ldd examples/.libs/mifare-desfire-info
examples/.libs/mifare-desfire-info:
	libfreefare.so.0 => not found (0)
	libnfc.so.5 => /usr/local/lib/libnfc.so.5 (0x800a34000)
	libm.so.5 => /lib/libm.so.5 (0x800c55000)
	libcrypto.so.8 => /usr/local/lib/libcrypto.so.8 (0x800e7d000)
	libc.so.7 => /lib/libc.so.7 (0x8012d0000)
	libusb.so.3 => /usr/lib/libusb.so.3 (0x80167b000)
	libthr.so.3 => /lib/libthr.so.3 (0x80188e000)
% ./libtool --mode=execute ldd examples/mifare-desfire-info
/home/romain/Projects/libfreefare/examples/.libs/mifare-desfire-info:
	libfreefare.so.0 => /usr/home/romain/Projects/libfreefare/libfreefare/.libs/libfreefare.so.0 (0x800820000)
	libnfc.so.5 => /usr/local/lib/libnfc.so.5 (0x800a3e000)
	libm.so.5 => /lib/libm.so.5 (0x800c5f000)
	libcrypto.so.8 => /usr/local/lib/libcrypto.so.8 (0x800e87000)
	libc.so.7 => /lib/libc.so.7 (0x8012da000)
	libusb.so.3 => /usr/lib/libusb.so.3 (0x801685000)
	libthr.so.3 => /lib/libthr.so.3 (0x801898000)

For this reason, the easier way of running a program in the debugger from the build directory is to do it this way:

./libtool --mode=execute gdb examples/mifare-desfire-info

Running the test suits

Some projects have a regression test suite which can be exercised by running:

make check

Refer to each project’s README for details about the presence of a test suite and the extra dependencies that it requires.

Using clang

clang is a C frontend for the LLVM compiler. As an alternative to gcc, it has advanced features that can help hunting bugs. An example that comes to mind is the address sanitizer which can be used by passing more variables to the configure script:

./configure CC="clang" CFLAGS="-O0 -g -fsanitize=address -fno-omit-frame-pointer"