如何理解 Gdb 中显示的一个奇怪的 memory 地址？

Question

I am debugging a memory issue with gdb. Gdb gives this error info:

runtime error: member access within misaligned address 0x0000006d20f4 for type 'struct deque', which requires 8 byte alignment
0x0000006d20f4: note: pointer points here
  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00
              ^ 

Question: How does the displayed address

 00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00

corresponds to "0x0000006d20f4"?

Answer 1

As you can read in the message itself, the memory address is 0x0000006d20f4 and the value you have highlighted are the contents of that memory location.

Answer 2

Hmm.... the pointer points to an address that is multiple of four, but not multiple of eight, so in my opinion, the pointer is pointing to the beginning of the shown block:

runtime error: member access within misaligned address 0x0000006d20f4 for type 'struct deque', which requires 8 byte alignment
0x0000006d20f4: note: pointer points here
  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00
  ^  this is actually where the pointer is pointing.
              ^ this is actually address 0x0000006d20f8, which should be correctly  8byte aligned.  Probably where the pointer should be pointing.

Should it be possible to check struct deque definition, and determine that you are not wrong and it doesn't require to be eight byte aligned? Have you mangled 32bit architecture definitions with 64bit architecture systems? Please, post the code, not your idea of what can be happening. You think you are correct, so it is very difficult, from your ideas, to see where is your mistake. Where did you get the memory to store the struct deque object?