Dumping contents of lost memory reported by Valgri

Question

When I run valgrind --leak-check=yes on a program, a few bytes of lost memory are reported. Is it possible to view the contents of this memory (i.e. dump the data that is stored in it)?

Answer 1

You can do that with the last version of Valgrind (3.8.1):

Start your executable activating the gdbserver at startup:

valgrind --vgdb-error=0 ....<your program>

Then in another window, connect a gdb to Valgrind (following the indications given by Valgrind). Then put a breakpoint at a relevant place (e.g. at the end of main) and use the gdb

continue

command till the breakpoint is reached. Then do a leak search from gdb:

   monitor leak_check full reachable any

Then list the address(es) of the reachable blocks of the relevant loss record nr

   monitor block_list <loss_record_nr>

You can then use gdb features to examine the memory of the given address(es). Note also the potentially interesting command "who_points_at" if you are searching who has kept a pointer to this memory.