How do you access flags in assembly?
Accessing FLAGS directly
- PUSHF / POPF Push/pop 16-bit FLAGS onto/from the stack.
- PUSHFD / POPFD Push/pop 32-bit EFLAGS onto/from the stack.
- PUSHFQ / POPFQ Push/pop 64-bit RFLAGS onto/from the stack.
Can Eflags be set directly?
Some flags can be set or cleared directly with specific instructions: CLC, STC, and CMC: clear, set, and complement the carry flag. CLI and STI: clear and set the interrupt flag (which should be done atomically) CLD and STD: clear and set the direction flag.
Which instruction uses flags?
Arithmetic and logical instructions set some or all of the flags, and conditional jump instructions take variable action based on the value of certain flags. For example, jz (Jump if Zero), jc (Jump if Carry), and jo (Jump if Overflow) depend on specific flags.
How many x86 instructions are there?
According to Intel’s XED, as of this writing, there are 1503 defined x86 instructions (“iclasses” in XED lingo), from AAA to XTEST (this includes AMD-specific extensions too, by the way).
Why is it called x86 and not x32?
x86 is the name of the architecture that it’s built to run on (the name comes from a series of old Intel processors, the names of which all ended in 86, The first of which was the 8086). Although x86 was originally a 16-bit architecture, the version in use today is the 32-bit extension.
Can you fly two flags on one pole?
Yes, you can fly two flags from the same flagpole. You just need to have two sets of snap hooks, and they can be on the same rope or halyard. The United States flag will always go on top. Typically you leave approximately one foot of space between the United States flag and the flag underneath.
When is the overflow flag set in x86?
In x86 assembly, the overflow flag is set when an add or sub operation on a signed integer overflows, and the carry flag is set when an operation on an unsigned integer overflows. However, when it comes to the inc and dec instructions, the situation seems to be somewhat different.
Which is the lower byte of the FLAGS register?
If you need only the lower byte of the flags register (which contains SF,ZF,AF,PF,CF), then there is the odd but convenient instruction LAHF (ha ha), which loads the bottom 8 bits of the flags register into AH, and its counterpart SAHF to store AH into flags.
Can you set the VM and RF flags with POPF?
Note that you cannot set the VM and RF flags with POPF — they retain their previous values. Similarly, you can only change the I/O privilege level when executing at privilege level 0, and the interrupt flag can only be changed when executing at a privilege level at least as privileged as the I/O privilege level.
How is CMP is actually setting the flags?
How cmp is actually setting the flags? CMP performs a subtraction but does not store the result. The CF, OF, SF, ZF, AF, and PF flags are set according to the result. I suggest you read up on the OF and CF here: http://teaching.idallen.com/dat2343/10f/notes/040_overflow.txt