如何在链接存档文件和所有存档文件时将库版本信息添加到elf文件中有其版本信息？

Question

I am creating an ELF file by linking object files with some archive files. But when I run the "what" command on my ELF file I can see lib info (version) for some archive files only, not all.

Why does the ELF file have only info for some files even it linked to all archive files? (PS: All archive files have their version info, check in below example)

Example:

$ ld -o bos_epb.ppc.elf a.o b.o c.o -L/home/xrava/lib/powerpc \
  --start-group -lgcc -lm -lcrt -lsslcrypto -lssh --end-group

When I run "what" on the ELF file I can see lib info about libcrt only, not all.

$ what bos_epb.ppc.elf
bos_epb.ppc.elf:
    Lib crt swfp version BL910288
    C Run Time Library
    Built Fri 22 Apr 2016 23:31:21 +0200 by tefo@
    Copyright 2016 XXXXXXX

All my archives have their version info but not writing this to elf except libcrt.

>>what libssh.a 
libssh.a: 
Lib ssh swfp version BL910291 
SSH Built Wed 27 Apr 2016 23:36:24 +0200 by tefo@ 
Copyright 2016 XXXXXXXX

Answer 1

All my archives have their version info but not writing this to elf except libcrt.

In order to understand this result, you need to understand

1. How the what command works and
2. How the linker works.

On with the show. The what command is very simple: it scans an arbitrary binary looking for and ASCII string starting with "special" symbol sequence @(#) and prints any string that follows that sequence (ending with the NUL character). Documentation .

In order for the string @(#) Lib ssh swfp version BL910291 to appear in the linked executable bos_epb.ppc.elf , the object file containing that string must be selected from libssh.a to become part of the executable. Which brings us to issue #2 above.

Just because such an object is present in libssh.a , you can't assume that it will be linked into the final binary. The algorithm that the linker uses to decide whether to include an object into the final executable or not is described here or here .

You can garantee that the entire libssh.a is included in the final binary by using -Wl,--whole-archive -lssh -Wl,--no-whole-archive , but this is ill -advised. It may cause your binary to fail to link, and is guaranteed to make it larger than it should be.