initial version of nob.sl

2026-01-09 15:45:36 +01:00
parent c31d8b93ce
commit e967e0d044
2 changed files with 132 additions and 0 deletions
--- a/nob.sl
+++ b/nob.sl
@@ -0,0 +1,127 @@
+# Minimal nob-style helper: run a shell command via /bin/sh -c
+
+# : sh ( cmd_addr cmd_len -- exit_code )
+# Runs `/bin/sh -c <cmd>` and returns a waitpid-style exit code
+# (WIFEXITED ? status>>8 : 128+signal). Returns neg errno on fork/exec failure.
+:asm sh {
+    ; stack: cmd_len (TOS), cmd_addr (NOS)
+    push r15              ; preserve callee-saved
+    push r14
+    push r13
+    push rbx
+
+    mov rbx, [r12]        ; len
+    mov r13, [r12 + 8]    ; addr (preserve across syscalls)
+    add r12, 16           ; pop args
+
+    mov r14, rbx          ; len
+    inc r14               ; size = len + 1
+
+    ; mmap buffer for C-string command
+    mov rax, 9            ; mmap
+    xor rdi, rdi          ; NULL addr
+    mov rsi, r14          ; size
+    mov rdx, 3            ; PROT_READ | PROT_WRITE
+    mov r10, 34           ; MAP_PRIVATE | MAP_ANON
+    mov r8, -1            ; fd = -1
+    xor r9, r9            ; offset = 0
+    syscall
+    cmp rax, -4095
+    jae .mmap_fail
+    mov r15, rax          ; cmd buffer
+
+    ; copy cmd into buffer and add NUL
+    mov rcx, rbx          ; len
+    mov rdi, r15          ; dst
+    mov rsi, r13          ; src
+    rep movsb
+    mov byte [r15 + rbx], 0
+
+    ; fork
+    mov rax, 57           ; fork
+    syscall
+    cmp rax, 0
+    jl .fork_fail
+    cmp rax, 0
+    jne .parent
+
+.child:
+    ; child: argv = "/bin/sh" "-c" cmd NULL
+    sub rsp, 56
+    lea rbx, [rel .sh_path]
+    mov [rsp], rbx            ; argv[0]
+    lea rbx, [rel .dash_c]
+    mov [rsp + 8], rbx        ; argv[1]
+    mov [rsp + 16], r15       ; argv[2]
+    mov qword [rsp + 24], 0   ; argv[3] = NULL
+    lea rsi, [rsp]            ; argv
+    mov qword [rsp + 32], 0   ; envp[0] = NULL
+    lea rdx, [rsp + 32]       ; envp
+    lea rdi, [rel .sh_path]   ; filename
+    mov rax, 59               ; execve
+    syscall
+    mov rdi, 127
+    mov rax, 60               ; exit
+    syscall
+
+.parent:
+    ; rax holds child pid
+    mov rbx, rax              ; child pid
+    sub rsp, 8
+    lea rsi, [rsp]            ; status*
+    xor rdx, rdx              ; options = 0
+    xor r10, r10              ; rusage = NULL
+    mov rdi, rbx              ; pid
+    mov rax, 61               ; wait4
+    syscall
+    mov eax, [rsp]
+    add rsp, 8
+
+    ; decode exit status: if signaled -> 128+signal, else (status >> 8) & 0xff
+    mov ebx, eax
+    and ebx, 0x7f
+    cmp ebx, 0
+    jne .got_signal
+    shr eax, 8
+    and eax, 0xff
+    jmp .status_ready
+.got_signal:
+    mov eax, ebx
+    add eax, 128
+.status_ready:
+    mov edi, eax              ; save for return after unmap
+
+    ; munmap command buffer
+    mov rax, 11               ; munmap
+    mov rdi, r15              ; addr
+    mov rsi, r14              ; size
+    syscall
+
+    mov eax, edi
+    sub r12, 8
+    mov [r12], rax
+    pop rbx
+    pop r13
+    pop r14
+    pop r15
+    ret
+
+.fork_fail:
+    mov rax, rax              ; rax holds neg errno
+    jmp .cleanup_return
+
+.mmap_fail:
+    mov rax, -12              ; -ENOMEM
+.cleanup_return:
+    sub r12, 8
+    mov [r12], rax
+    pop rbx
+    pop r13
+    pop r14
+    pop r15
+    ret
+
+.sh_path: db "/bin/sh", 0
+.dash_c:  db "-c", 0
+}
+;