Re: Weird assembly code behavior

[Andreas Gustafsson <gson%gson.org@localhost>]

Emmanuel Dreyfus wrote:
> Here rsp = 0x18001a4
[...]
>    0xe85d5f <memcpy+15>:        lea    -0x8(%rdi,%rdx,1),%r9
> That instruction changed rsp to 0x18001a3
> 
>    0xe85d60 <memcpy+16>:        lea    -0x8(%rdi,%rdx,1),%ecx

This looks like the processor is in a 32-bit mode but executing code
that was generated for 64-bit mode, and the debugger is disassembling
the code assuming a 64-bit mode.

Would the byte at 0xe85d5f by 0x4C by any chance?  This means "dec SP"
in 32-bit mode, which would explain why the stack pointer is decremented
and why the program counter increases only by 1 (since it's a one-byte
instruction), but in 64-bit mode it's a REX register prefix that's part
of a longer instruction.
-- 
Andreas Gustafsson, gson%gson.org@localhost