Register EDI holds the bit offset …

software | Windows |

EDI: The Destination Index

Every loop that generates data must store the result in memory, and
doing so requires a moving pointer. The destination index, EDI, is that
 pointer. The destination index holds the implied write address of all
 string operations. The most useful string instruction, remarkably
 enough, is the seldom-used STOS. STOS copies data from the
 accumulator into memory and increments the destination index. This
 one-byte instruction is perfect, since the final result of any calculation
 should be in the accumulator anyhow, and storing results in a moving
 memory address is a common task.

source :

software | GNU/Linux |

(gdb) info registers
rax            0xfffffffffffffdfc	-516
rbx            0x5dc	1500
rcx            0xffffffffffffffff	-1
rdx            0x5dc	1500
rsi            0x1	1
rdi            0x7fffedb60c40	140737181518912
rbp            0x23c7160	0x23c7160
rsp            0x7fffedb60bf0	0x7fffedb60bf0
r8             0x0	0
r9             0xffffffff	4294967295
r10            0x8	8
r11            0x246	582
r12            0x7fffedb60c40	140737181518912
r13            0x7fffedb60c50	140737181518928
r14            0x0	0
r15            0x1	1
rip            0x7fc4a09070c8	0x7fc4a09070c8
eflags         0x246	[ PF ZF IF ]
cs             0x33	51
ss             0x2b	43
ds             0x0	0
es             0x0	0
fs             0x0	0
gs             0x0	0

rdi 0x7fffedb60c40 140737181518912

The RAX, RBX, RCX, RDX, RBP, RSI, RDI, and RSP registers are used by both 32-bit and 64-bit binaries. However, in 32-bit mode, only the low 32 bits of these registers are accessible by 32-bit binaries. In the x86 architecture, these registers are EAX, EBX, ECX, EDX, EBP, ESI, EDI, and ESP. source :

| Related Discussion |

knut st. osmundsen 2007-02-09 18:29:55 EST Description of problem: Crashing at __lll_mutex_timedlock_wait+148 (/lib64/tls/ lock cmpxchg %edx,(%rdi) Because the syscall wasn't made and %rdi hasn't been loaded with %r12 yet. Version-Release number of selected component (if applicable): glibc-3.4.0 How to fix: Move the mov %r12,%rdi instruction up somewhere before the je 8f. How to reproduce: This isn't easy to reproduce and I'm not going to write a testcase for it since it's a very obvious bug in the code. But, my from the situation I get it in is that it requires a 2nd thread to signal the condition variable /mutex (I'm not quite sure which it is) while the crashing thread is engaging a sleep. source :

| Variation |

Hardware 64 bit. Windows OS 32 bit so uses EDI. GNU/Linux 64 bit version so used RDI. Links(s).