Use info symbol gdb command. 16 Examining the Symbol Table.
info symbol addr
Print the name of a symbol which is stored at the address addr. If no symbol is stored exactly at addr, gdb prints the nearest symbol and an offset from it:
(gdb) info symbol 0x54320
_initialize_vx + 396 in section .text
This is the opposite of the info address command. You can use it to find out the name of a variable or a function given its address.
For dynamically linked executables, the name of executable or shared library containing the symbol is also printed:
(gdb) info symbol 0x400225
_start + 5 in section .text of /tmp/a.out
(gdb) info symbol 0x2aaaac2811cf
__read_nocancel + 6 in section .text of /usr/lib64/libc.so.6