GDB find command error "warning: Unable to access x bytes of target memory at y, halting search"

Question

I'm trying to find current flag count in KMines by using gdb. I know that I should look for memory mappings first to avoid non-existent memory locations. So I ran info proc mappings command to see the memory segments. I picked up a random memory gap (0xd27000-0x168b000) from the result and executed the find command like this: find 0x00d27000, 0x0168b000, 10

But I got the warning: Unable to access 1458 bytes of target memory at 0x168aa4f, halting search. error. Although the address 0x168aa4f is between 0xd27000 and 0x168b000, gdb says that it can't access to it. Why does this happen? What can I do to avoid this situation? Or is there a way to ignore unmapped/unaccessible memory locations?

Edit: I tried to set the value of the address 0x168aa4f to 1 and it works, so gdb can actually access that address but gives error when used with the find command. But why?

Answer 1

I guess I have solved my own problem, I can't believe how simple the solution was. The only thing I did was to decrease the 2nd parameter's value by one. So the code should be find 0x00d27000, 0x0168afff, 10 because linux allocates the memory by using maps in [x,y) format, so if the line in root/proc/pid/maps says something like this;

01a03000-0222a000 rw-p

The memory allocated includes 0x01a03000 but not 0x0222a000. Hope this silly mistake of mine helps someone :D

Edit: The root of the problem is the algorithm implemented in target.c(gdb's source code I mean) the algorithm reads and searches the memory as chunks at the size of 16000 bytes. So even if the last byte of the chunk is invalid, gdb will throw the entire chunk into the trash and won't even give any proper information about the invalid byte, it only reports the beginning of the current chunk.