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Apr 2, 2014 · cmpb $0x0,(%edx) is this comparing whatever is pointed to edx to the byte of 0, and 0 in ...
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Oct 29, 2017 · I am doing alright with following the assembly dump of the program (so far) but am stuck on understanding cmpb instruction set. I've recorded the value in the respective registers, but am lost as to what is happening with the values in the registers when cmpb is called.
Jan 9, 2014 · asm("cmpb $0,(%esi)"); // compare value at address stored in %esi with literal 0 (end of string) I suggest that you compile the code with debug information, like. $ g++ -g -o sample sample.c. It is then quite easy to debug the program: $ gdb sample. (gdb) run. Starting program: sample. sh: cls: command not found.
Oct 4, 2015 · 25. According to my understanding cmpl compares unsigned. It does both, in a way. The difference in signed vs. unsigned is here the usage of the jump instructions. For >, there is ja for unsigned and jg for signed (jump if above and jump if greater). For <, there is jb for unsigned and jl for signed (jump if below and jump if less).
Jan 15, 2013 · 1. But after looking at the disassembly, it appears to be fetching a 32-bit operand. But why, especially since this is a 64-bit mode program and 64-bit assembly language AND the only register specified in the instruction is %rsp, which is a 64-bit register. – honestann. Jan 14, 2013 at 23:55. 1. Looks that way. As long as I can be sure, I'm okay.
May 31, 2015 · I used an example included in the emulator8086 to work my way out. name "cmpsb". org 100h. ; set forward direction: cld. ;read from keyboard. mov dx, offset teclado. mov ah, 0ah. int 21h.
Jan 24, 2017 · The reason REP works is because rep has the same encoding as REPE (F3h). In principle REPE is the right thing to use here, but depending on your assembler it might just take REP as correct. So in reality you have a REPE cmpsb there, it's just that your (dis)assembler doesn't really know. answered May 11, 2012 at 14:15.
Mar 4, 2019 · is_ascii_lowercase_v2: subl $97, %edi cmpb $25, %dil setbe %al movzbl %al, %eax ret I could never get clang to reproduce exactly the same sequence of instructions. It likes to use add $-97, %edi, and cmp with $26 / setb. Or it will do really interesting (but sub-optimal) things like this:
Oct 21, 2018 · d double 8 bytes. t temporary 10 bytes. For example, cmpb is the instruction cmp with a 1 byte operand size indicated. However, your code uses %rdi as an operand which is a quad-word (64 bit) register, so the assembler rightfully complains that this is the wrong operand. To fix this issue, simply leave out the size suffix; the assembler is able ...
