Using library files and writing library files on AIX

It’s been a long time that dynamic link libraries, static libraries, static links, dynamic links, and recently run-time links have been messed up. Everyone knows that the static link is a compile-time link, the generated file is large, the dynamic link is a runtime link, and the generated file is small. I don't know everyone, or everyone thinks that they know... sometimes windows, sometimes linux, sometimes Aix, sometimes gcc, sometimes g++, sometimes cc, sometimes xlc, sometimes .so, sometimes .a, sometimes .dll sometimes .lib sometimes .o, too much inconsistency, too much trouble. Also, because of work, I often use Aix as the working environment. Some say that .so is a dynamic link library, and .a is a static link library, but it doesn't look like it on Aix. This weekend, I spent two days researching these problems on Aix, using vac's xlc and ccs ld. I can't say how much I know now, but at least not as confused as before. Do a summary now.

One, link file and link method. In fact, not carefully thinking about dynamic linking and dynamic linking is the main reason for my confusion. The reason why I think of this problem is to write a library a in the work, then I have to compile a, then write another library b, b depends on a, I have to compile b, in the process, I began to think, I used the link method when I compiled a. I want to use a now. What is a? So I began to distinguish between the link file and the link method, started the following experiment 1, using the library file libc.a, statically linked into the executable program hello.c

C code copy code #include <stdio.h> Int main() { printf("Hello, world!\ "); } #include <stdio.h>int main() {printf("Hello, world!\ ");}Run# xlc - o hello.o -c hello.c Generate the target file hello.o Run ld -o hello_s -bstatic hello.o -lc I want to statically link hello.o and libc.a and generate the executable hello_s. I didn't use xlc directly to generate executable files. I wanted to figure out each step. The price of the result is a lot of time and endless search. -bnso is telling ld static links. (You can also use the -E and -S parameters of xlc to look at the pre-processing and assembly files of hello.c, and then use as to compile the assembly file to generate the object file.) Result ld: 0711-327 WARNING: Entry point not found: __start Ld: 0711-244 ERROR: No csects or exported symbols have been saved. Here is not found __start, this __start looks a lot like a sub-process of the system. The reason for this error is because we did not add such a library /usr/lib/crt0.o when linking. If you use xlc to directly link statically, then this library should be added by xlc itself (this library seems to be a thread) Initialization related), you can use the nm command to view the symbol associated with this target file, which contains __start. So we run ld -o hello_s -bstatic hello.o -lc /usr/lib/crt0.o The result is that a lot of symbols can't be found, ld: 0711-224 WARNING: Duplicate symbol: .is_posix_tz ld: 0711- 224 WARNING: Duplicate symbol: .__icuinit ld: 0711-345 Use the -bloadmap or -bnoquiet option to obtain more information. ld: 0711-317 ERROR: Undefined symbol: __loadx ld: 0711-317 ERROR: Undefined symbol: _system_TB_config ld: 0711-317 ERROR: Undefined symbol: errno ld: 0711-317 ERROR: Undefined symbol: .___bzero ld: 0711-317 ERROR: Undefined symbol: smcr_timebase ld: 0711-317 ERROR: Undefined symbol: .___memmove ld: 0711-317 ERROR : Undefined symbol: .___memset ld: 0711-317 ERROR: Undefined symbol: _system_configuration ld: 0711-317 ERROR: Undefined symbol: disclaim ld: 0711-317 ERROR: Undefined symbol: kwritev ld: 0711-317 ERROR: Undefined symbol: kpwritev Ld: 0711-317 ERROR: Undefined symbol: kpwrite ld: 0711-317 ERROR: Undefined symbol: kwrite ld: 0711-317 ERROR: Undefined symbol: kopenx ... ld prompt -bloadmap to see the specific error message, so I run ld -o hello_s -bstatic hello.o -lc /usr/lib/crt0.o -bloadmap:out.txt and view the output file to get... ld: 0711- 318 ERROR: Undefined symbols were found. The following symbols are in error: Symbol Inpndx TY CL Source-File(Object-File) OR Import-File{Shared-object} RLD: Address Section Rld-type Referencing Symbol ----- -------------------------------------------------- --------------------------------------- __loadx [262] ER DS (/usr/lib /libc.a[shr.o]) 0006919c .data R_POS [1658] <__loadx> _system_TB_config [792] ER UA (/usr/lib/libc.a[shr.o]) 000691a8 .data R_POS [1664] < ;_system_TB_config> errno [8] ER UA (/usr/lib/libc.a[shr.o]) 00068e3c .data R_POS [1226] ... This is some of the definitions in shr.o in libc.a The symbol can't be found, so we solve this shr.o, run ar -x /usr/lib/libc.a shr.o to get shr.o, then ldd shr.o get the output shr.o needs: /unix /Usr/lib/libcrypt.a(shr.o) /usr/lib/libc.a(shr.o) this s Hr.o needs the above three libraries, libc.a we have included, then where to find /unix this library? The symbols that are not found now should be system calls. Check the ld manual to know that we need to import the symbol table /lib/syscalls.exp of the system call. So we run # ld -o hello_s -bstatic hello.o -lc /usr/lib/crt0.o -bI:/lib/The result of syscalls.exp still reports error # ld -o hello_s -bstatic hello.o -lc /usr/lib/crt0.o -bI:/lib/syscalls.exp ld: 0711-224 WARNING: Duplicate symbol: .open ld: 0711 -224 WARNING: Duplicate symbol: .openx ld: 0711-224 WARNING: Duplicate symbol: .is_posix_tz ld: 0711-224 WARNING: Duplicate symbol: .__icuinit ld: 0711-224 WARNING: Duplicate symbol: .send ld: 0711-224 WARNING: Duplicate symbol: .nrecvmsg