diff options
Diffstat (limited to 'twasm')
| -rw-r--r-- | twasm/README.md | 32 |
1 files changed, 32 insertions, 0 deletions
diff --git a/twasm/README.md b/twasm/README.md index b414770..c7dc833 100644 --- a/twasm/README.md +++ b/twasm/README.md @@ -6,6 +6,11 @@ this will be a self hosted, very minimal subset of nasm-style 64 bit asm I want to compile Bootler and Twasm with the Twasm assembler +### reading + +- [instructions](https://www.felixcloutier.com/x86/) +- [opcodes,ModR/M,SIB](http://ref.x86asm.net/coder64.html) (no secure site available) + ### memory map ``` @@ -197,3 +202,30 @@ hlt 0xFE0A ; newline 0xFE00 ; null terminator ``` + +#### nasm output with the above example program, bits 64 + +```nasm +0x31 ; XOR r/m16/32/64 r16/32/64 +0xC0 ; ModR/M byte + ; mod 11b ; directly address the following: + ; reg 000b ; EAX + ; r/m 000b ; EAX + +0x48 ; 64 Bit Operand Size prefix +0xFF ; with `reg` from ModR/M byte 000b: + ; INC r/m16/32/64 +0xC0 ; ModR/M byte + ; mod 11b ; direct addressing + ; reg 000b ; RAX + ; r/m 000b ; RAX + +0x48 ; 64 Bit Operand Size prefix +0x89 ; MOV r/m16/32/64 r16/32/64 +0x10 ; ModR/M byte + ; mod 00b ; indirect addressing, no displacement + ; reg 010b ; RDX + ; r/m 000b ; [RAX] + +0xF4 ; HLT +``` |