mem.S

Makefile

LDFLAGS += -Wl,--build-id=none -nostdlib -s
run: mem
	strace -eraw=all ./mem >/dev/null
mem: mem.S
	$(CC) $(ASFLAGS) $(CPPFLAGS) $(LDFLAGS) $(TARGET_MACH) $^ $(LOADLIBES) $(LDLIBS) -o $@
mem-translated: mem-translated.c
	$(CC) $(CFLAGS) $(CPPFLAGS) $(LDFLAGS) $(TARGET_MACH) $^ $(LOADLIBES) $(LDLIBS) -o $@
.PHONY: run

mem-translated.c

#include <asm/param.h>
#include <sys/syscall.h>
#ifndef _syscall1
# define _syscall1(type, name, arg1) ({ \
    long __syscall_rc; \
    __asm__ volatile ( \
            "syscall" \
            : "=a" (__syscall_rc) \
            : "a" (SYS_##name), "D" (arg1) \
            : "%rcx", "%r11", "memory"); \
    (type) __syscall_rc; \
})
#endif
#ifndef _syscall2
# define _syscall2(type, name, arg1, arg2) ({ \
    long __syscall_rc; \
    __asm__ volatile ( \
            "syscall" \
            : "=a" (__syscall_rc) \
            : "a" (SYS_##name), "D" (arg1), "S" (arg2) \
            : "%rcx", "%r11", "memory"); \
    (type) __syscall_rc; \
})
#endif
#ifndef _syscall3
# define _syscall3(type, name, arg1, arg2, arg3) ({ \
    long __syscall_rc; \
    __asm__ volatile ( \
            "syscall" \
            : "=a" (__syscall_rc) \
            : "a" (SYS_##name), "D" (arg1), "S" (arg2), "d" (arg3) \
            : "%rcx", "%r11", "memory"); \
    (type) __syscall_rc; \
})
#endif
static char proc_self_maps[] = "/proc/self/maps";
static char buffer[EXEC_PAGESIZE];
int _start() {
    char c;
    int rc, sz, i, r;
    long val, save;
    rc = _syscall2(int, open, proc_self_maps, 0);
    if (rc >= 0) {
        sz = _syscall3(int, read, rc, buffer, EXEC_PAGESIZE);
        if (sz >= 0) {
            _syscall1(int, close, rc);
            i = 0;
            while (i < sz) {
                save = val;
                val = 0;
                while (1) {
                    c = buffer[i++];
                    r = 1 << (c & 0x1f);
                    if (!(r & 0x3ff007e)) break;
                    if (r & 0x7e) c -= 7;
                    val = (val << 4) + (c & 0xf);
                }
                if (c == '-') continue;
                while (i < sz && buffer[i++] != '\n');
                while (save < val) {
                    _syscall3(int, write, 1, save, EXEC_PAGESIZE);
                    save += EXEC_PAGESIZE;
                }
            }
            rc = 0;
        }
    }
    _syscall1(void, exit, rc);
}

mem.S

#include <asm/param.h>
#include <sys/syscall.h>

.data
proc_self_maps:
    .asciz "/proc/self/maps"

.bss
buffer:
    .skip EXEC_PAGESIZE

.text
.globl _start
_start:
    mov $SYS_open, %rax
    mov $proc_self_maps, %rdi
    mov $0, %rsi
    syscall
    mov %rax, %rdi
    test $0, %rdi
    jl die
    mov $SYS_read, %rax
    mov $buffer, %rsi
    mov $EXEC_PAGESIZE, %rdx
    syscall
    mov %rax, %r12
    cmp $0, %r12
    jl die
    mov $SYS_close, %rax
    syscall
    mov $0, %r13
line0:
    cmp %r12, %r13
    jge exit
    mov %rdx, %rbx
    mov $0, %rdx
hex0:
    mov buffer(%r13), %cl
    inc %r13
    mov $1, %eax
    rol %cl, %eax
    test $0x3ff007e, %eax
    jz hex2
    test $0x7e, %eax
    jz hex1
    sub $7, %cl
hex1:
    and $0xf, %rcx
    shl $4, %rdx
    add %rcx, %rdx
    jmp hex0
hex2:
    cmp $'-', %cl
    jz line0
    mov $'\n', %al
    mov $buffer, %rdi
    add %r13, %rdi
    mov %r12, %rcx
    sub %r13, %rcx
    mov $buffer, %rsi
    repne scasb (%rdi)
    sub $buffer, %rdi
    mov %rdi, %r13
    mov $1, %rdi
    mov %rbx, %rsi
    mov %rdx, %rbx
    mov $EXEC_PAGESIZE, %rdx
line1:
    cmp %rsi, %rbx
    jle line0
    mov $SYS_write, %rax
    syscall
    add $EXEC_PAGESIZE, %rsi
    jmp line1
exit:
    mov $0, %rdi
die:
    mov $SYS_exit, %rax
    syscall