Symbol addresses in ELF - symbols

Question

I am trying to read ELF symbol table.
I am facing following discrepancy in shared libraries and can't understand the reason behind it.
For libc, using readelf i got following output.
Num: Value Size Type Bind Vis Ndx Name
7: 00000033c32160b0 146 FUNC WEAK DEFAULT 11 realloc##GLIBC_2.2.5
8: 00000033c3421000 4 OBJECT WEAK DEFAULT 21 _dl_starting_up##GLIBC_PRIVATE
9: 00000033c32118f0 382 FUNC GLOBAL DEFAULT 11 _dl_allocate_tls##GLIBC_PRIVATE
10: 00000033c3421280 40 OBJECT GLOBAL DEFAULT 21 _r_debug##GLIBC_2.2.5
11: 00000033c341fdc8 8 OBJECT GLOBAL DEFAULT 17 __libc_stack_end##GLIBC_2.2.5
12: 00000033c3215f30 252 FUNC WEAK DEFAULT 11 __libc_memalign##GLIBC_2.2.5
13: 00000033c3211a70 140 FUNC GLOBAL DEFAULT 11 _dl_deallocate_tls##GLIBC_PRIVATE
14: 00000033c3216040 52 FUNC WEAK DEFAULT 11 calloc##GLIBC_2.2.5
15: 00000033c341fc88 8 OBJECT GLOBAL DEFAULT 17 _dl_argv##GLIBC_PRIVATE
16: 00000033c3211000 599 FUNC GLOBAL DEFAULT 11 _dl_mcount##GLIBC_2.2.5
and for my own shared library build using following commands
gcc -rdynamic -Wint-to-pointer-cast -g -fPIC -lpthread -c probes.c -ldl -lelf
gcc -shared -lpthread -Wl,--no-as-needed,-soname,libprobes.so.1 -o libprobes.so.1 mutrace.o -ldl -lelf
the output was
Num: Value Size Type Bind Vis Ndx Name
.
.
.
34: 00000000000040d0 66 FUNC GLOBAL DEFAULT 11 pthread_create
35: 0000000000001d72 109 FUNC GLOBAL DEFAULT 11 thread_local_init
36: 0000000000002b21 481 FUNC GLOBAL DEFAULT 11 trylock_ret_event
37: 00000000000030c4 652 FUNC GLOBAL DEFAULT 11 lock_init_event
38: 0000000000003e4d 130 FUNC GLOBAL DEFAULT 11 pthread_mutex_init
39: 0000000000004668 0 FUNC GLOBAL DEFAULT 12 _fini
40: 0000000000003dd0 125 FUNC GLOBAL DEFAULT 11 pthread_cond_timedwait
41: 0000000000001b03 92 FUNC GLOBAL DEFAULT 11 backtrace
42: 0000000000001b5f 94 FUNC GLOBAL DEFAULT 11 backtrace_symbols
43: 0000000000002ee3 481 FUNC GLOBAL DEFAULT 11 unlock_ret_event
44: 0000000000004026 95 FUNC GLOBAL DEFAULT 11 pthread_mutex_trylock
45: 0000000000003531 476 FUNC GLOBAL DEFAULT 11 lock_destroy_event
46: 0000000000004112 1012 FUNC GLOBAL DEFAULT 11 print_symtable
For libc the symbol values are absolute ( virtual address ) but in my library, the values are relative. What decides this behaviour ?
I have tried following the information from http://docs.oracle.com/cd/E19082-01/819-0690/chapter6-35166/index.html , but latter when i checked the ELF header, both the libraries had same type.

Answer 1

for my own shared library build using following commands
gcc -rdynamic -Wint-to-pointer-cast -g -fPIC -lpthread -c probes.c -ldl -lelf
gcc -shared -lpthread -Wl,--no-as-needed,-soname,libprobes.so.1 -o libprobes.so.1
These commands are incorrect. The first one is a compilation command (because of -c flag). The linker options (-rdynamic, -lpthread, etc.) don't belong on it.
The second command is link command, and has the wrong library order. In addition, you forgot to actually use probes.o that you compiled. This would be better:
gcc -shared -o libprobes.so.1 -Wl,-soname=libprobes.so.1 probes.o -lpthread
For libc the symbol values are absolute
No, they are not. Your libc has apparently been prelinked at address 0x33c3210000 (or similar). That doesn't make the symbols absolute. You can undo prelinking (read man prelink) and you'll see similar "relative" addresses in libc.so.6.