Special Meaning for Pointer Value 0x7c7c7c7c

Question

While debugging a Linux app, I found a pointer with the suspicious value 0x7c7c7c7c. Does that particular value indicate anything?

(I ask because I know from my MSVC days that in a debug build, values like 0xcdcdcdcd or 0xdddddddd would be stored into heap blocks that were uninitialized, freed, or otherwise invalid. Some people use magic values like 0xdeadbeef or 0xcafebabe in uninitialized memory. I'm guessing something in libc or elsewhere uses 0x7c7c7c7c as a magic value, but I can't find it documented.)

Answer 1

0x7c7c = 01111100 01111100 in binary. That could be one of those "most difficult to read" bit patterns that format utilities fill unused space on hard drives with.

Answer 2

I don't recognize that magic number, and neither does Wikipedia. I would guess that some code in your program (or in a library you're using) is using memset() and hitting your pointer. Have you grepped your code base case-insensitively for the string "0x7c"?

Answer 3

0x7C is an ASCII pipe "|" character. You could search for writes of that character as well 124 and 0x7C as Adam suggested.

Answer 4

Maybe the MALLOC_PERTURB_ environment variable is set? If set, it influences how malloc() initializes the allocated memory.