Support passing registers to printf

src/bss/buffers.asm

@@ -1,2 +1,6 @@
 generic_buffer_512 resb 512
 
+printf_arg_1_buf resb 8
+printf_arg_2_buf resb 8
+printf_arg_3_buf resb 8
+

src/printf.asm

@@ -11,9 +11,12 @@
     %xdefine num_args %count(%{2:-1})
 
     %if num_args == 1
-        printf_args_1 %1, %{2:-1}
+        mov qword [printf_arg_1_buf], %{2:2}
+        printf_args_2 %1, 1
     %elif num_args == 2
-        printf_args_2 %1, %{2:-1}
+        mov qword [printf_arg_1_buf], %{2:2}
+        mov qword [printf_arg_2_buf], %{3:3}
+        printf_args_2 %1, 2
     %else
         jmp %%error_many_args
     %endif
@@ -37,88 +40,9 @@
     pop_registers
 %endmacro
 
-; ARGS 1
-
-%macro printf_args_1 2
-    ; printdf [format str] [int]
-    push_registers
-
-    ; TODO: do not segfault when we write out of those bounds
-    %define MAX_PRINTF_LEN 2048
-
-    ; rax = is null terminated format str
-    str_to_stack %1
-
-    sub rsp, MAX_PRINTF_LEN
-    ; r10 is index in final output string
-    mov r10, 0
-    ; r11 is pointer to start of output string
-    lea r11, [rbp-MAX_PRINTF_LEN]
-
-    mov rcx, 0
-%%printf_fmt_char_loop:
-    mov r9b, byte [rax+rcx]
-    inc rcx
-
-    ; copy one letter from the format string
-    ; to the output buffer
-    mov byte [r11+r10], r9b
-    inc r10
-
-    cmp r9b, '%'
-    jne %%printf_fmt_char_loop_check_repeat
-
-%%printf_fmt_char_loop_got_percentage:
-    mov r9b, byte [rax+rcx]
-    cmp r9b, 'd'
-    jne %%printf_fmt_char_loop_check_repeat
-
-%%printf_fmt_char_loop_got_fmt_d:
-
-    ; overwrite the %d
-    dec r10
-    inc rcx
-
-    push rax
-    push rdi
-
-    mov rax, %2
-    lea rdi, [r11+r10]
-    call int32_to_str
-    add r10, rax
-
-    pop rdi
-    pop rax
-%%printf_fmt_char_loop_check_repeat:
-
-    cmp r9b, 0
-    jne %%printf_fmt_char_loop
-
-    ; print output buffer
-    dec r10
-    printn r11, r10
-
-    ; frees stack string
-    ; and copy buffer
-    mov rsp, rbp
-
-    ; TODO: support \n escape sequence
-    call print_newline
-
-    pop_registers
-%endmacro
-
-; ARGS 2
-
-; this is basically a copy of args 1
-; there has to be a neater way to do this
-;
-; if it wasnt a macro but a function
-; it could partially replace only one argument at a time
-; and then it could be called recursively
-
-%macro printf_args_2 3
-    ; printdf [format str] [int] [int]
+%macro printf_args_2 2
+    ; printdf [format str] [num args]
+    ;  needs the labels [printf_arg_1_buf] and [printf_arg_2_buf] to be filled
     push_registers
 
     ; TODO: do not segfault when we write out of those bounds
@@ -178,14 +102,14 @@
     exit 1
 
 %%printf_fmt_char_loop_got_fmt_d_arg_1:
-    mov rax, %{2:2}
+    mov rax, [printf_arg_1_buf]
     lea rdi, [r11+r10]
     call int32_to_str
     add r10, rax
     jmp %%printf_fmt_char_loop_got_fmt_d_arg_end
 
 %%printf_fmt_char_loop_got_fmt_d_arg_2:
-    mov rax, %{3:3}
+    mov rax, [printf_arg_2_buf]
     lea rdi, [r11+r10]
     call int32_to_str
     add r10, rax
@@ -210,6 +134,14 @@
     ; TODO: support \n escape sequence
     call print_newline
 
+    cmp r8, %2
+    je %%printf_args_end
+
+    puts "error: printf number of args does not match number of args in format string"
+    exit 1
+
+    %%printf_args_end:
+
     pop_registers
 %endmacro
 

tests/printf_test.asm

@@ -3,4 +3,11 @@
 _start:
     printf "hello %d world", 10
     printf "%d %d foo bar", 777, -1
+
+    mov rcx, 0
+    printf "rcx=%d (should be zero)", rcx
+
+    mov rcx, 1
+    printf "rcx=%d (should be one)", rcx
+
     exit 0