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
glibc 2.15 operates multiple allocation arenas. Each arena has its own lock. When a thread needs to allocate memory, malloc() picks an arena, locks it, and allocates memory from it. The mechanism for choosing an arena is somewhat elaborate and is aimed at reducing lock contention: /* arena_get() acquires an arena and locks the corresponding … Read more
m conversion specifier is not C but is a GNU extension to printf: From GNU documentation: http://www.gnu.org/software/libc/manual/html_node/Other-Output-Conversions.html The ‘%m’ conversion prints the string corresponding to the error code in errno. See Error Messages. Thus: fprintf (stderr, “can’t open `%s’: %m\n”, filename); is equivalent to: fprintf (stderr, “can’t open `%s’: %s\n”, filename, strerror (errno)); The ‘%m’ … Read more
I have found the answer to my question myself:) So what I didn’t understand was how the glibc could differentiate between a Segfault and a corrupted double-linked list, because according to my understanding, from perspective of glibc they should look like the same thing. Because if I implement a double-linked list inside my program, how … Read more
The C Standard does not provide data structures like linked list and stack.Some compiler implementations might provide their own versions but their usage will be non portable across different compilers. So Yes, You have to write your own.
The following analysis applies only to glibc (based on the ptmalloc2 algorithm). There are certain options that seem helpful to return the freed memory back to the system: mallopt() (defined in malloc.h) does provide an option to set the trim threshold value using one of the parameter option M_TRIM_THRESHOLD, this indicates the minimum amount of … Read more
Its the implementation of Standard C library described in C standards plus some extra useful stuffs which are not strictly standard but used frequently. Its main contents are : 1) C library described in ANSI,c99,c11 standards. It includes macros, symbols, function implementations etc.(printf(),malloc() etc) 2) POSIX standard library. The “userland” glue of system calls. (open(),read() … Read more
I was able to install libc6 2.17 in Debian Wheezy by editing the recommendations in perror’s answer: IMPORTANT You need to exit out of your display manager by pressing CTRL–ALT–F1. Then you can stop x (slim) with sudo /etc/init.d/slim stop (replace slim with mdm or lightdm or whatever) Add the following line to the file … Read more
even easier use ldd –version This should return the glibc version being used i.e. $ ldd –version ldd (GNU libc) 2.17 Copyright (C) 2012 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO … which is the same result as running my libc library $ /lib/libc.so.6 GNU … 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