Archive for November 2012
Today, it was the second time I stepped on an interesting problem with GCC (well, it is actually a behavior). I created a function which returns a
void* in a .c file. This C file was then compiled and added in a library (.a). When I used this function in an application, I was getting a
void* pointer were the 32 most significant bits were either zeroed (
0x00000000...) or set to 1 (
0xFFFFFFFF...). My application is 64bit!!
For example, the debug prints I added would return:
[lib] allocated 0x7f756d6fa048 [app] allocated 0x6d6fa048
where you can see the “conversion”.
What was the problem? After some time of debugging, I realized that I had forgotten to include the aforementioned function in the corresponding header file :|. So, although GCC could find the function in the library I was linking the application to, I guess it was assuming a wrong return value/header for that function.
The conclusion: Be more careful 😉
PS. I am using the following version of GCC:
$ gcc -v Using built-in specs. COLLECT_GCC=gcc COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.6/lto-wrapper Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.6.3-1ubuntu5' --with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.6 --enable-shared --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.6 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --enable-plugin --enable-objc-gc --disable-werror --with-arch-32=i686 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5)