Summary: NASM/YASM requires word [ecx] when the operand-size isn’t implied by the other operand. (Otherwise [ecx] is ok). MASM/TASM requires word ptr [ecx] when the operand-size isn’t implied by the other operand. (Otherwise [ecx] is ok). They each choke on the other’s syntax. WARNING: This is very strange area without any ISO standards or easy-to-find … Read more
From the nasm documentation: The SECTION directive (SEGMENT is an exactly equivalent synonym) Nasm can produce output in various formats, some of which support sections. Certain section names can be arbitrary (such as the three you listed), for them only the section flags count. The predefined ones are just convenience shortcuts, .text is marked as … Read more
When the function is called, the stack looks like: +————-+ | Parameter 2 | +————-+ | Parameter 1 | +————-+ | Return Addr | <– esp +————-+ then after the “stack frame” is set up: +————-+ | Parameter 2 | <– [ebp + 12] +————-+ | Parameter 1 | <– [ebp + 8] +————-+ | … Read more
The square brackets essentially work like a dereference operator (e.g., like * in C). So, something like mov REG, x moves the value of x into REG, whereas mov REG, [x] moves the value of the memory location where x points to into REG. Note that if x is a label, its value is the … Read more
MASM (Microsoft Assembler) is the popular assembler for Windows. MASM is for 16-bit and 32-bit applications(x86). ML64 is the one for 64 bit sources (AMD64/x86-64) NASM (Netwide Assembler) is the popular assembler for Linux but is available on Windows too. NASM supports 16-bit, 32 bit and 64 bit programs. FASM (Flat Assembler) is available for … Read more
This is a possible assembly code of int x = plus_10(40); push 40 ; push argument call plus_10 ; call function retadd: add esp, 4 ; clean up stack (dummy pop) ; result of the function call is in EAX, per the calling convention ; if compiled without optimization, the caller might just store it: … Read more
PC Assembly Language is my favorite resource on assembly programming. It’s modern, free, and covers a variety of topics. It uses NASM and the examples are available for Linux (among several other systems).
There is e.g. Writing A Useful Program With NASM and of course the obvious http://www.nasm.us/doc/nasmdoc3.html. There are a couple of sample programs at http://www.csee.umbc.edu/help/nasm/sample.shtml If you are looking for a more general introduction to assembly programming there is The Art of Assembly Programming and the wikipedia page on NASM references Assembly Language Step by Step … Read more
Looking at the nasm source, it looks like: ‘oword”https://stackoverflow.com/”DO’ is 8 times as big as “word” (O for “octoword”), synonymous with dqword (“double-quad”); that would be 128 bits, corresponding to the size of an SSE vector register. ‘tword”https://stackoverflow.com/”DT’ is 80 bits (T for “ten bytes”), the full size of an Intel x87 floating point register. … Read more
global directive is NASM specific. It is for exporting symbols in your code to where it points in the object code generated. Here you mark _start symbol global so its name is added in the object code (a.o). The linker (ld) can read that symbol in the object code and its value so it knows … Read more