Gcc

GCC 基本选项如表 1 所示。

影响 GCC 及其预处理器的环境变量分别如表 3 和表 4 所示。

参考：https://gcc.gnu.org/onlinedocs/gcc/Environment-Variables.html

用链接器的 -z defs 或 -no-undefined 可以检测 unresolved symbols。

$ cat silly.c
#include <stdio.h>

void forgot_to_define(FILE *fp);

void doit(const char *filename)
{
    FILE *fp = fopen(filename, "r");
    if (fp != NULL)
    {
        forgot_to_define(fp);
        fclose(fp);
    }
}

$ gcc -shared -fPIC -o libsilly.so silly.c && echo succeeded || echo failed
succeeded

$ gcc -Wl,z,defs -shared -fPIC -o libsilly.so silly.c && echo succeeded || echo failed
/tmp/ccmfaNa8.o: In function `doit':
silly.c:(.text+0x35): undefined reference to `forgot_to_define'
collect2: ld returned 1 exit status
failed

参考：http://stackoverflow.com/questions/1617286/easy-check-for-unresolved-symbols-in-shared-libraries

The linker uses the following search paths to locate required shared libraries:

1. Any directories specified by -rpath-link options.
   
2. Any directories specified by -rpath options. The difference between -rpath and -rpath-link is that directories specified by -rpath options are included in the executable and used at runtime, whereas the -rpath-link option is only effective at link time. Searching -rpath in this way is only supported by native linkers and cross linkers which have been configured with the --with-sysroot option.
   
3. On an ELF system, for native linkers, if the -rpath and -rpath-link options were not used, search the contents of the environment variable LD_RUN_PATH.
   
4. On SunOS, if the -rpath option was not used, search any directories specified using -L options.
   
5. For a native linker, search the contents of the environment variable LD_LIBRARY_PATH.
   
6. For a native ELF linker, the directories in DT_RUNPATH or DT_RPATH of a shared library are searched for shared libraries needed by it. The DT_RPATH entries are ignored if DT_RUNPATH entries exist.
   
7. The default directories, normally /lib and /usr/lib.
   
8. For a native linker on an ELF system, if the file /etc/ld.so.conf exists, the list of directories found in that file.
   

If the required shared library is not found, the linker will issue a warning and continue with the link.

参考：https://sourceware.org/binutils/docs/ld/Options.html

Adding a subroutine's entry to the call stack is sometimes called "winding"; conversely, removing entries is "unwinding".

参考：http://en.wikipedia.org/wiki/Call_stack#Description

使用下面命令可以查看编译器会搜索的 include path：

$ gcc -E -Wp,-v -xc /dev/null
$ g++ -E -Wp,-v -xc++ /dev/null

如何查看当前系统的 GLIBC 版本？

方法 1：

$ ldd --version
GNU C Library stable release version 2.5, by Roland McGrath et al.
Copyright (C) 2006 Free Software Foundation, Inc.

方法 2：

$ /lib/libc.so.6
GNU C Library stable release version 2.5, by Roland McGrath et al.
Copyright (C) 2006 Free Software Foundation, Inc.