glibc

I am working in glibc and I need to get the id of the current thread. For this i use syscall(SYS_gettid); Issue is, i am forced to include bits/syscall.h instead of ideal case i.e sys/syscall.h . sys/syscall.h internally calls bits/syscall.h but that is wrapped with #ifndef _LIBC macro. i.e #ifndef _LIBC /* The Linux kernel header file defines macros `__NR_<name>', but some programs expect the traditional form `SYS_<name>'. So in building libc we scan the kernel's list and produce <bits/syscall.h> with macros for all the `SYS_' names. */ # include <bits/syscall.h> #endif also bits/syscall.h

I am trying to link my program statically with glibc, because version of the glibc on the target machine is pretty much unpredictable. I used linker flags -static-libgcc and -static-libstdc++ and it worked fine. The executable is big, but I can live with it. Unfortunately, when I run my executable on the target machine (it is named 'mytest' in the example below) I get the following error: ./mytest: /usr/lib64/libstdc++.so.6: version `GLIBCXX_3.4.11' not found (required by libboost_log.so.1.53.0) ./mytest: /usr/lib64/libstdc++.so.6: version `GLIBCXX_3.4.15' not found (required by libboost_log

Is the GNU function asprintf (print to allocated string) thread-safe? (IIC, basically, this boils down to the question whether malloc is thread-safe.) Consider the example code: #define _GNU_SOURCE #include <stdio.h> #include "getValue.h" char * getValue(int key) { char * value; asprintf(&value, "%d", key); // TODO: No error handling! // If memory allocation wasn't possible, or some other error occurs, these functions will // return -1, and the contents of strp is undefined. return value; } Here, I do not touch any global variables. What if my getValue gets called in concurrent threads? No bad

I'm working on a C application that has to walk $PATH to find full pathnames for binaries, and the only allowed dependency is glibc (i.e. no calling external programs like which). In the normal case, this just entails splitting getenv("PATH") by colons and checking each directory one by one, but I want to be sure I cover all of the possible corner cases. What gotchas should I look out for? In particular, are relative paths, paths starting with ~ meant to be expanded to $HOME, or paths containing the : char allowed? One thing that once surprised me is that the empty string in PATH means the

I need to use an alternate glibc version, newer than the one installed on my system ( 2.18 vs 2.15 ). Several related issues are covered here and here . The specific question I'm asking here is the following: I set up the library path of the new dynamic linker ( ld-2.18.so ) so that the new libc ( libc-2.18.so ) is found ahead of the old libc ( libc-2.15.so ). However, when I try to run a program with the new ld , the old version of libc is picked up, generating a SEGV . Why is that happening? Note: I know this can be fixed by using --rpath at compile time or LD_LIBRARY_PATH at run time.

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版权声明：本文由陈福荣原创文章，转载请注明出处: 文章原文链接： https://www.qcloud.com/community/article/184 来源：腾云阁 https://www.qcloud.com/community 接上篇： 十问 Linux 虚拟内存管理 (glibc) (一) 五.free 的内存真的释放了吗（还给 OS ） ? 前面所有例子都有一个很严重的问题，就是分配的内存都没有释放，即导致内存泄露。原则上所有 malloc/new 分配的内存，都需 free/delete 来释放。但是， free 了的内存真的释放了吗？ 要说清楚这个问题，可通过下面例子来说明。 初始状态：如图 (1) 所示，系统已分配 ABCD 四块内存，其中 ABD 在堆内分配， C 使用 mmap 分配。为简单起见，图中忽略了如共享库等文件映射区域的地址空间。 E=malloc(100k) ：分配 100k 内存，小于 128k ，从堆内分配，堆内剩余空间不足，扩展堆顶 (brk) 指针。 free(A) ：释放 A 的内存，在 glibc 中，仅仅是标记为可用，形成一个内存空洞 ( 碎片 ) ，并没有真正释放。如果此时需要分配 40k 以内的空间，可重用此空间，剩余空间形成新的小碎片。 free(C) ： C 空间大于 128K ，使用 mmap 分配，如果释放 C ，会调用

[root@uranuspreapp30 opt]# strings /lib64/libc.so.6 | grep GLIBC |tail -n 8 strings: '/lib64/libc.so.6': No such file [root@uranuspreapp30 opt]# 首先想到的是不是系统安装的时候没有装libc，于是执行 [root@localhost ~]# rpm -qa | grep libc 执行结果： libcurl-7.19.7-26.el6_2.4.x86_64 libcap-2.16-5.5.el6.x86_64 libcgroup-0.37-4.el6.x86_64 glibc-2.12-1.166.el6_7.7.i686 libcom_err-devel-1.41.12-12.el6.x86_64 libcroco-0.6.2-5.el6.x86_64 libcap-ng-0.6.4-3.el6_0.1.x86_64 libcanberra-0.22-1.el6.x86_64 glibc-common-2.12-1.166.el6_7.7.x86_64 glibc-devel-2.12-1.166.el6_7.7.x86_64 libcurl-devel-7.19.7-26.el6_2.4.x86_64 libcom_err-1.41

前言 需要安装MySQL5.6.16，的确没有安装过，找安装包都找了很久。还是安装成功了。记录下，方便以后再次安装有文档。 如果已经安装了MySQL，请把所有库导出来，并把一些不兼容的地方去掉 通过MySQL用户删除/var/lib/mysql/目录下所有文件 su mysql rm -fr /var/lib/mysql/* exit 安装MySQL yum install -y wget wget https://cdn.mysql.com/archives/mysql-5.6/MySQL-5.6.16-1.linux_glibc2.5.x86_64.rpm-bundle.tar yum remove mariadb-libs-1:5.5.60-1.el7_5.x86_64 yum install -y perl-ExtUtils-CBuilder perl-ExtUtils-MakeMaker tar -xvf MySQL-5.6.16-1.linux_glibc2.5.x86_64.rpm-bundle.tar rpm -ivh MySQL-server-5.6.16-1.linux_glibc2.5.x86_64.rpm rpm -ivh MySQL-client-5.6.16-1.linux_glibc2.5.x86_64.rpm rpm -ivh MySQL-devel