CODEWITHSUNDEEP
c++gdb
Nathaniel Flath
Nathaniel Flath

Reputation: 16025

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

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?

Upvotes: 44

Views: 117071

Answers (3)

ks1322
ks1322

Reputation: 35845

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

Upvotes: 70

Brian Vandenberg
Brian Vandenberg

Reputation: 4121

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.

Upvotes: 16

Mark B
Mark B

Reputation: 96301

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.

Upvotes: 2

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