How to use GDB to find what function a memory address corresponds to

Question

I am using google's heap checker to track down a memory leak. It gives me a stack trace such as:

Leak of 21 bytes in 1 objects allocated from:                                                                                                                                                               
    @ 0xf6088241                                                                                                                                                                                               
    @ 0xf60890d2                                                                                                                                                                                               
    @ 0xf6089246                                                                                                                                                                                               
    @ 0x8054781                                                                                                                                                                                                
    @ 0x8054862                                                                                                                                                                                                
    @ 0xf684ee76                                                                                                                                                                                               
    @ 0xf684f343                                                                                                                                                                                               
    @ 0x804be4c                                                                                                                                                                                                
    @ 0x80544f6                                                                                                                                                                                                
    @ 0xf5e52bb6                                                                                                                                                                                               
    @ 0x804b101

How do I determine what functions/lines of code these memory addresses correspond to?

I am surprised Google's heap checker does not do this conversion for you. Are you sure you compiled with "-g"? (Also, take a look at the [addr2line command](http://sourceware.org/binutils/docs/binutils/addr2line.html)) — Nemo, Oct 03 '11 at 19:04
Any symbol type question: http://stackoverflow.com/questions/762628/gdb-getting-a-symbol-name-from-a-memory-address — Ciro Santilli Путлер Капут 六四事, Jul 17 '15 at 09:10

score 56 · Accepted Answer · edited Sep 28 '18 at 05:11

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

So, after I got a list of info commands, and figured out that `info address` doesn't lookup address, turned out there's also a `info symbol` command, which doesn't query a symbol. — Hi-Angel, Jul 17 '16 at 17:35

score 9 · Answer 2 · answered Jun 29 '17 at 18:15

The original question asked how to do this in GDB:

# NOT what you want; note the lack of '*':
(gdb) info symbol 0xfde09edc
blah() + 388 in section .text of /tmp/libblah.so

# IS what you want; note the presence of '*':
(gdb) info line *0xfde09edc
Line 91 of "blah.cc"
   starts at address 0xfde09ebc <blah()+356>
   and ends at 0xfde09ee4 <blah()+396>

The * is necessary for info line and shouldn't be used for info symbol.

You can also use the disassemble command with its /m flag:

(gdb) disassemble /m 0xfde09edc

... though it's rather verbose and info line gives exactly what was requested.

Please note that `/m` modifier is deprecated in favor of `/s` (appeared in gdb 7.11). Anyway, you can use much less verbose output of `x/i 0xfde09edc` instead of disassembling the whole function. — Ruslan, Jul 12 '17 at 19:32

score 2 · Answer 3 · answered Oct 03 '11 at 19:34

2

Assuming your binary has debug information g++ -g you may be able to use x/ to get the info, I know that works for vtables.

x/<num>xw to print <num> hex words of memory, and gdb will annotate the left side with information about what's at the address.

answered Oct 03 '11 at 19:34

Mark B

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How to use GDB to find what function a memory address corresponds to

3 Answers3

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