如何在符号表中添加共享库版本信息

Question

I wrote a small simple test program that uses libz. I compiled it using

$gcc -o test test.c -lz

To see how libz functions are added to my symbol table I ran the following command

$ readelf -s test | grep inflate

Here is the output

 1: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND inflateEnd
 8: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND inflate
13: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND inflateInit_
51: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND inflateEnd
62: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND inflate
73: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND inflateInit_

libz that I am using has .gnu.version_d section defined as follows

Version definition section '.gnu.version_d' contains 7 entries:
Addr: 0x0000003175e014c0  Offset: 0x0014c0  Link: 4 (.dynstr)
000000: Rev: 1  Flags: BASE   Index: 1  Cnt: 1  Name: libz.so.1
0x001c: Rev: 1  Flags: none  Index: 2  Cnt: 1  Name: ZLIB_1.2.0
0x0038: Rev: 1  Flags: none  Index: 3  Cnt: 2  Name: ZLIB_1.2.0.2
0x0054: Parent 1: ZLIB_1.2.0
0x005c: Rev: 1  Flags: none  Index: 4  Cnt: 2  Name: ZLIB_1.2.0.8
0x0078: Parent 1: ZLIB_1.2.0.2
0x0080: Rev: 1  Flags: none  Index: 5  Cnt: 2  Name: ZLIB_1.2.2
0x009c: Parent 1: ZLIB_1.2.0.8
0x00a4: Rev: 1  Flags: none  Index: 6  Cnt: 2  Name: ZLIB_1.2.2.3
0x00c0: Parent 1: ZLIB_1.2.2
0x00c8: Rev: 1  Flags: none  Index: 7  Cnt: 2  Name: ZLIB_1.2.2.4
0x00e4: Parent 1: ZLIB_1.2.2.3

So why is libz version not part of libz function symbols in my symbol table. I expect to see something like -

1: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND inflateEnd@@ZLIB_1.2.0
...

Also .gnu.version_r section of my binary does not list libz version as a requirement. How can I add libz version dependency here?

$readelf -V test

...
Version needs section '.gnu.version_r' contains 1 entries:
Addr: 0x0000000000400618  Offset: 0x000618  Link: 6 (.dynstr)
000000: Version: 1  File: libc.so.6  Cnt: 1
 0x0010:   Name: GLIBC_2.2.5  Flags: none  Version: 2

Answer 1

Just because your libz contains versioning information does not mean that every symbol within is versioned. In my libz (version 1.2.3 (yes, really)), some of the external symbols are versioned and some are not, as I can determine via readelf . Specifically, all of the symbols you asked about are defined by my DSO, but none of them are versioned.

If you link against unversioned symbols, you should neither expect nor want the corresponding symbol references in your binary to be versioned.