gdb freezes in malloc

Question

Suppose I have some C program like this:

#include 
#include 

int main()
{
    while (true) {
        void *p = malloc(1000)         


        

Answer 1

If the 'finish' solution doesn't work for you. Here is another idea.

You can check if you are in malloc when you break the program. Based on the boolean in/out you skip calling the print commands. Here is a working example.

# gdb script: pygdb-logg.gdb
# easier interface for pygdb-logg.py stuff
# from within gdb: (gdb) source -v pygdb-logg.gdb
# from cdmline: gdb -x pygdb-logg.gdb -se test.exe

# first, "include" the python file:
source -v pygdb-logg.py

# define shorthand for inMalloc():
define inMalloc
  python inMalloc()
end

The associated python file:

# gdb will 'recognize' this as python
#  upon 'source pygdb-logg.py'
# however, from gdb functions still have
#  to be called like:
#  (gdb) python print logExecCapture("bt")

import sys
import gdb
import os

def logExecCapture(instr):
  # /dev/shm - save file in RAM
  ltxname="/dev/shm/c.log"

  gdb.execute("set logging file "+ltxname) # lpfname
  gdb.execute("set logging redirect on")
  gdb.execute("set logging overwrite on")
  gdb.execute("set logging on")
  gdb.execute("bt")
  gdb.execute("set logging off")

  replyContents = open(ltxname, 'r').read() # read entire file
  return replyContents

# in malloc?
def inMalloc():
  isInMalloc = -1;
  # as long as we don't find "Breakpoint" in report:
  while isInMalloc == -1:
    REP=logExecCapture("n")
#Look for calls that have '_malloc' in them 
    isInMalloc = REP.find("_malloc")
    if(isInMalloc != -1):
#       print ("Malloc:: ", isInMalloc, "\n", REP)
       gdb.execute("set $inMalloc=1")
       return True
    else:
#       print ("No Malloc:: ", isInMalloc, "\n", REP)
       gdb.execute("set $inMalloc=0")
       return False

gdb -x pygdb-logg.gdb -se test.exe

From the command line or script,

(gdb) inMalloc
(gdb) print $inMalloc

From an actual test program:

Program received signal SIGINT, Interrupt.
0x00007ffff7a94dba in _int_malloc (av=<optimized out>, bytes=1) at malloc.c:3806
3806    malloc.c: No such file or directory.
(gdb) inMalloc
(gdb) if $inMalloc
 >print $inMalloc
 >end
$1 = 1

I believe your script can use a similar 'if' structure to do/not do printf

Most of this was knocked off from here

Answer 2

The reason you're froze is probably a lock that's being held by your program, and is also required by printf. When you try to aquire it twice - you fail.

A possible WA is when breaking your program to call printf, just before you make the call, type finish - it will cause the current function to complete and return to the main frame. This will ensure the lock is free before you call printf.