8f256f1f2e
This is a 3-operand instruction: r32 = rm32 * imm32 It looks like https://c9x.me/x86/html/file_module_x86_id_138.html has a bug, implying the same opcode supports a 2-operand version. I don't see that in the Intel manual pdf, or at alternative sites like https://www.felixcloutier.com/x86/imul Native runs seem to validate my understanding. In the process I also fixed a bug in the existing multiply instruction 0f af: the only flags it sets are OF and CF. The other existing multiply instruction f7 was doing things right.
27 lines
923 B
Plaintext
27 lines
923 B
Plaintext
# Multiply 2 numbers.
|
|
#
|
|
# To run:
|
|
# $ ./bootstrap translate init.linux apps/ex14.subx -o apps/ex14
|
|
# $ ./bootstrap run apps/ex14
|
|
# Expected result:
|
|
# $ echo $?
|
|
# 6
|
|
|
|
== code
|
|
# instruction effective address register displacement immediate
|
|
# . op subop mod rm32 base index scale r32
|
|
# . 1-3 bytes 3 bits 2 bits 3 bits 3 bits 3 bits 2 bits 2 bits 0/1/2/4 bytes 0/1/2/4 bytes
|
|
|
|
Entry:
|
|
b8/copy-to-eax 1/imm32
|
|
b9/copy-to-ecx 2/imm32
|
|
bb/copy-to-ebx 3/imm32
|
|
|
|
69/multiply 3/mod/direct 1/rm32/ecx . . . 3/r32/ebx 3/imm32 # ebx = ecx * 3
|
|
|
|
$exit:
|
|
# exit(ebx)
|
|
e8/call syscall_exit/disp32
|
|
|
|
# . . vim:nowrap:textwidth=0
|