From 6b45b84ab1303b26d06233eb1b41c1ddd4074cc5 Mon Sep 17 00:00:00 2001
From: Kwarde <kevin@kwarde.com>
Date: Sat, 26 Jul 2025 00:20:25 +0200
Subject: [PATCH] printf->__INTERNAL_fmt. FD passed via RAX. fwrite now allows
 specifiers and variable arguments.

---
 src/console.asm | 21 ++++++++++++++++----
 src/file.asm    | 51 +++++++++++++++++++++++++------------------------
 src/tests.asm   | 25 ++++++++++++++++++++++++
 3 files changed, 68 insertions(+), 29 deletions(-)

diff --git a/src/console.asm b/src/console.asm
index 111b9fb..d623eb2 100644
--- a/src/console.asm
+++ b/src/console.asm
@@ -11,6 +11,8 @@ section .bss
 	printfBuff	resb	printfBuffLen
 	printfArgs	resq	5 ;5=>rsi,rdx,rcx,r8,r9
 section .text
+	global	__INTERNAL_fmt
+
 	global	print
 	global	puts
 	global	printf
@@ -94,13 +96,23 @@ puts:
 ;	r12	Padding length
 ;	r13	Bitmask, 1 = insert specifier yes/no, 2 = use zeroes for padding yes/no
 ;	r14	Keeps track of amount of processed format specifiers
+;	r15	Stores fd to write output to (passed to __INTERNAL_fmt via RAX)
 printf:
+	mov	rax, FD_stdout
+	jmp	__INTERNAL_fmt
+
+__INTERNAL_fmt:
 	%macro load_arg 1
 	cmp	r14, 4
 	ja	%%fromStack
 	mov	%1, [printfArgs + SIZE_QWORD * r14]
 	jmp	%%continue
 	%%fromStack:
+	cmp	r15, FD_stdout
+	je	%%stackNoShift
+	mov	%1, [rbp + (RBP_OFFSET_CALLER*2 + SIZE_QWORD) + ((r14-5) * SIZE_QWORD)] ;non-printf functions calling __INTERNAL_fmt require RDI to be FD, all args shifted and rbp+RBP_OFFSET_CALLER to r9. Also requires function prologue and a CALL to __INTERNAL_fmt (not a JMP like in printf); hence the RBP_OFFSET_CALLER*2
+	jmp	%%continue
+	%%stackNoShift:
 	mov	%1, [rbp + RBP_OFFSET_CALLER + ((r14-5) * SIZE_QWORD)]
 	%%continue:
 	%endmacro
@@ -152,10 +164,11 @@ printf:
 	; entry:
 	push	rbp
 	mov	rbp, rsp
-	sub	rsp, SIZE_QWORD
 	push	r12
 	push	r13
 	push	r14
+	push	r15
+	mov	r15, rax
 
 	cmp	byte [rdi], EOS
 	je	.emptyStr
@@ -414,7 +427,7 @@ printf:
 	push	rdx
 	push	r11
 	mov	rax, NR_write
-	mov	rdi, FD_stdout
+	mov	rdi, r15
 	lea	rsi, [rel printfBuff]
 	mov	rdx, r10
 	syscall
@@ -435,7 +448,7 @@ printf:
 
 	.wrapup:
 	mov	rax, NR_write
-	mov	rdi, FD_stdout
+	mov	rdi, r15
 	lea	rsi, [rel printfBuff]
 	mov	rdx, r10
 	mov	r10, r11
@@ -447,9 +460,9 @@ printf:
 	xor	rax, rax
 
 	.quit:
+	pop	r15
 	pop	r14
 	pop	r13
 	pop	r12
-	add	rsp, SIZE_QWORD
 	leave
 	ret
diff --git a/src/file.asm b/src/file.asm
index dcd9a62..db953d2 100644
--- a/src/file.asm
+++ b/src/file.asm
@@ -1,5 +1,7 @@
 %include "src/constants.asm"
 
+extern	__INTERNAL_fmt
+
 extern	strlen
 extern	umask_get
 
@@ -76,7 +78,7 @@ fopen:
 	call	fexist
 	pop	rsi
 	pop	rdi
-	mov	rax, 1
+	test	rax, 1
 	jz	%%createFile
 	jmp	%1
 	%%createFile:
@@ -86,7 +88,7 @@ fopen:
 	pop	rdi
 	push	rdi
 	not	rax
-	mov	rsi, 00666q
+	mov	rsi, 0666q
 	and	rsi, rax
 	mov	rax, NR_creat
 	syscall
@@ -155,6 +157,7 @@ fopen:
 ;	rax*	(ret)
 ;	rdi	(arg) Pointer to opened file
 fclose:
+	sub	rsp, SIZE_QWORD
 	cmp	rdi, 3
 	jl	.invalid_fd ;disallow closing stdin,stdout,stderr
 	mov	rax, NR_close
@@ -165,6 +168,7 @@ fclose:
 	mov	rax, -EINVAL
 
 	.quit:
+	add	rsp, SIZE_QWORD
 	ret
 
 ;----- fexist(*file[]) -----;
@@ -174,7 +178,7 @@ fclose:
 ;	rax*	(ret)
 ;	rdi	(arg) Pointer to string holding (path+)file name
 fexist:
-	;sub	rsp, SIZE_QWORD
+	sub	rsp, SIZE_QWORD
 	mov	rsi, 'r'
 	call	fopen
 	test	rax, rax
@@ -186,35 +190,32 @@ fexist:
 	.not_exist:
 	xor	rax, rax
 	.quit:
-	;add	rsp, SIZE_QWORD
+	add	rsp, SIZE_QWORD
 	ret
 
-;--- fwrite(*filePointer, *data[]) -----;
-; Writes data to given file
+;--- fwrite(*filePointer, *data[], ...) -----;
+; Writes data to given file. Allows format specifiers and variable arguments (see `__INTERNAL_fmt` for supported specifiers)
 ; Return value: Length of given string(data[]), 0 if nothing was written (eg invalid file or file not writable, or data[] is empty)
 ; Used registers:
 ;	rax*	(ret)
 ;	rdi	(arg) Pointer to file
 ;	rsi	(arg) Data to write
-;	r8*	Backs up rdi
-;	r9*	Backs up rsi
 fwrite:
-	sub	rsp, SIZE_QWORD
+	push	rbp
+	mov	rbp, rsp
+	cmp	rdi, 2
+	jg	.cnt
 	xor	rax, rax
-	cmp	rdi, 3
-	jl	.quit
-	mov	r8, rdi
-	mov	r9, rsi
-
-	mov	rdi, rsi
-	call	strlen
-
-	mov	rdx, rax
-	mov	rax, NR_write
-	mov	rdi, r8
-	mov	rsi, r9
-	syscall
-
-	.quit:
-	add	rsp, SIZE_QWORD
+	leave
+	ret
+	.cnt:
+	mov	rax, rdi
+	mov	rdi, rsi
+	mov	rsi, rdx
+	mov	rdx, rcx
+	mov	rcx, r8
+	mov	r8, r9
+	mov	r9, [rbp + RBP_OFFSET_CALLER]
+	call	__INTERNAL_fmt
+	leave
 	ret
diff --git a/src/tests.asm b/src/tests.asm
index 5467e58..94797d2 100644
--- a/src/tests.asm
+++ b/src/tests.asm
@@ -330,6 +330,8 @@ section .rodata
 	addTest(fwrite1, "fwrite(fp1, 'Hello world!\n') //mode 'a'")
 	addTest(fwrite2, "fwrite(fp1, 'How are you doing?\n') //mode 'a'")
 	addTest(fwrite3, "fwrite(fp1, 'Howdy environment!') //mode 'w'")
+	addTest(fwrite4, "fwrite(fp1, ''%c%c%c%c%c%c%c%c\n'', 'H', 'e', 'l', 'l', 'o', '!', '?', '!')")
+	fwriteStr1	db	"%c%c%c%c%c%c%c%c\n",EOS
 
 section .bss
 	strBuff1	resb	64
@@ -1198,6 +1200,29 @@ _start:
 	call	fwrite
 	assert_eq(18)
 
+	; Re-open in write mode, again
+	mov	rdi, [fp1]
+	call	fclose
+	lea	rdi, [rel file1]
+	mov	rsi, 'w'
+	call	fopen
+	mov	[fp1], rax
+
+	; TEST 4
+	printTest(fwrite4)
+	mov	rdi, [fp1]
+	lea	rsi, [fwriteStr1]
+	mov	rdx, 'H'
+	mov	rcx, 'e'
+	mov	r8, 'l'
+	mov	r9, 'l'
+	push	byte '!'
+	push	byte '?'
+	push	byte '!'
+	push	byte 'o'
+	call	fwrite
+	add	rsp, SIZE_QWORD * 4
+
 	; Close file1
 	mov	rdi, [fp1]
 	call	fclose