Setup 1: glibc without dedicated GCC This setup might work and is quick as it does not recompile the whole GCC toolchain, just glibc. The only problem I have with this setup is that I haven’t found a nice way to use runtime objects such as crt1.o, crti.o, and crtn.o provided by our glibc, and … Read more
I am surprised that there is a problem, but it does seem to be a problem on Linux (I tested on Ubuntu 16.04 LTS running in a VMWare Fusion VM on my Mac) — but it was not a problem on my Mac running macOS 10.13.4 (High Sierra), and I wouldn’t expect it to be … Read more
Answer for Example Question unwind gave the accepted answer to the example question: Your code is wrong. You are allocating space for a single pointer (malloc(sizeof(char*))), but no characters. You are overwriting your allocated space with all the strings, causing undefined behavior (in this particular case, corrupting malloc()‘s book-keeping data). You don’t need to allocate … Read more
The C Standard does not define such an optional character in the scanf() formats. The GNU lib C, does define an optional a indicator this way (from the man page for scanf): An optional a character. This is used with string conversions, and relieves the caller of the need to allocate a corresponding buffer to … Read more
I think this is very annoying, and I think it is arrogant to call a feature “useless” because it has problems dealing with certain use cases. The biggest problem with the glibc approach is that it hard-codes paths to system libraries (gconv as well as nss), and thus it breaks when people try to run … Read more
You cannot update glibc on Centos 6 safely. However you can install 2.14 alongside 2.12 easily, then use it to compile projects etc. Here is how: mkdir ~/glibc_install; cd ~/glibc_install wget http://ftp.gnu.org/gnu/glibc/glibc-2.14.tar.gz tar zxvf glibc-2.14.tar.gz cd glibc-2.14 mkdir build cd build ../configure –prefix=/opt/glibc-2.14 make -j4 sudo make install export LD_LIBRARY_PATH=/opt/glibc-2.14/lib
If you compile your code with -nostdlib, you won’t be able to call any C library functions (of course), but you also don’t get the regular C bootstrap code. In particular, the real entry point of a program on Linux is not main(), but rather a function called _start(). The standard libraries normally provide a … Read more
Testing your code on Godbolt’s Compiler Explorer provides this explanation: at -O0 or without optimisations, the generated code calls the C library function strlen; at -O1 the generated code uses a simple inline expansion using a rep scasb instruction; at -O2 and above, the generated code uses a more elaborate inline expansion. Benchmarking your code … Read more
The code provided by eerpini does not work as written. Note, for example, that the pipe ends that are closed in the parent are used afterwards. Look at close(wpipefd[1]); and the subsequent write to that closed descriptor. This is just transposition, but it shows this code has never been used. Below is a version that … Read more
Update 2: see Andrew G Morgan’s slightly more complicated solution which does work for any GLIBC (that solution is also used in libc.so.6 itself (since forever), which is why you can run it as ./libc.so.6 (it prints version info when invoked that way)). Update 1: this no longer works with newer GLIBC versions: ./a.out: error … Read more