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57 lines
1.4 KiB
NASM
57 lines
1.4 KiB
NASM
; compile with:
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; $ [ny]asm -felf(32|64) -oe.o e.asm
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; $ (gcc|clang) -m(32|64) -oe e.o -nostdlib -nostartfiles
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section .text
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global _start
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%if __BITS__ == 32
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%define r(n) e%+n
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%define SYS_write 4
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%define rarg0 ebx
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%define rarg1 ecx
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%define rarg2 edx
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%define syscall int 0x80
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%else
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%define r(n) r%+n
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%define SYS_write 1
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%define rarg0 rdi
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%define rarg1 rsi
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%define rarg2 rdx
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default rel
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%endif
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; size of a Linux pipe buffer
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%define PIPE_SIZE 0x10000
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%define STDOUT_FILENO 1
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; Instead of simply storing a char in .rodata and write(2)-ing it
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; over and over again, we first fill a buffer full of e's, and *then*
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; write the entire buffer. This is much faster than the first option,
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; because we only need to issue a syscall once every 65536 bytes. (Remember
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; that doing a syscall requires the kernel to handle an interrupt etc etc etc.)
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_start:
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; allocate space for the message
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mov r(cx), PIPE_SIZE
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mov r(bx), r(cx) ; we'll need it later
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sub r(sp), r(cx)
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; quick memset(3)
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mov al, 'e'
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mov r(di), r(sp)
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rep stosb
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; push+pop is actually a smaller encoding than mov for ints that fit within 8 bit
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push STDOUT_FILENO
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pop rarg0
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mov rarg1, r(sp)
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mov rarg2, r(bx)
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.loop:
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; set this within the loop because the syscall's exit code is placed in r(ax)
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push SYS_write
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pop r(ax)
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syscall
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jmp short .loop
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