From 99da70deba62de235454ef1852745610a9c9f741 Mon Sep 17 00:00:00 2001
From: dzwdz
Date: Fri, 29 Jul 2022 21:33:15 +0200
Subject: user/libc: properly implement snprintf; the v*printf family

---
 src/user/app/tests/tests.c   | 10 ++++++++
 src/user/lib/include/stdio.h | 10 ++++++--
 src/user/lib/printf.c        | 59 ++++++++++++++++++++++++++++++--------------
 3 files changed, 59 insertions(+), 20 deletions(-)

diff --git a/src/user/app/tests/tests.c b/src/user/app/tests/tests.c
index 1d1156e..4390747 100644
--- a/src/user/app/tests/tests.c
+++ b/src/user/app/tests/tests.c
@@ -237,6 +237,15 @@ static void test_execbuf(void) {
 	test_fail();
 }
 
+static void test_snprintf(void) {
+	char buf[16];
+	memset(buf, '?', 16);
+	assert(13 == snprintf(buf, 15, "That's 0x%x", 0x1337));
+	assert(!memcmp(buf, "That's 0x1337\0??", 16));
+	assert(17 == snprintf(buf, 15, "%05x %05x %05x", 0, 0, 0));
+	assert(!memcmp(buf, "00000 00000 00\0?", 16));
+}
+
 static void test_misc(void) {
 	assert(_syscall(~0, 0, 0, 0, 0, 0) < 0); /* try making an invalid syscall */
 }
@@ -254,6 +263,7 @@ int main(void) {
 	run_forked(test_semaphore);
 	run_forked(test_efault);
 	run_forked(test_execbuf);
+	run_forked(test_snprintf);
 	run_forked(test_misc);
 	return 1;
 }
diff --git a/src/user/lib/include/stdio.h b/src/user/lib/include/stdio.h
index bf9e09e..fe754da 100644
--- a/src/user/lib/include/stdio.h
+++ b/src/user/lib/include/stdio.h
@@ -1,5 +1,6 @@
 #pragma once
 #include <bits/file.h>
+#include <stdarg.h>
 #include <stddef.h>
 
 #define EOF (-1)
@@ -8,8 +9,13 @@
 #define SEEK_CUR 2
 #define SEEK_END 3
 
-int printf(const char *fmt, ...);
-int snprintf(char *str, size_t len, const char *fmt, ...);
+int printf(const char *restrict fmt, ...);
+int fprintf(FILE *restrict f, const char *restrict fmt, ...);
+int snprintf(char *restrict str, size_t len, const char *restrict fmt, ...);
+
+int vprintf(const char *restrict fmt, va_list ap);
+int vfprintf(FILE *restrict f, const char *restrict fmt, va_list ap);
+int vsnprintf(char *restrict str, size_t len, const char *restrict fmt, va_list ap);
 
 int _klogf(const char *fmt, ...); // for kernel debugging only
 
diff --git a/src/user/lib/printf.c b/src/user/lib/printf.c
index 443c424..53b1140 100644
--- a/src/user/lib/printf.c
+++ b/src/user/lib/printf.c
@@ -5,47 +5,70 @@
 
 
 static void backend_file(void *arg, const char *buf, size_t len) {
-	fwrite(buf, 1, len, (FILE *)arg);
+	fwrite(buf, 1, len, arg);
 }
 
-int printf(const char *fmt, ...) {
-	int ret = 0;
-	va_list argp;
-	va_start(argp, fmt);
-	ret = __printf_internal(fmt, argp, backend_file, (void*)stdout);
-	va_end(argp);
-	return ret;
+int vfprintf(FILE *restrict f, const char *restrict fmt, va_list ap) {
+	return __printf_internal(fmt, ap, backend_file, f);
 }
 
 static void backend_buf(void *arg, const char *buf, size_t len) {
 	char **ptrs = arg;
 	size_t space = ptrs[1] - ptrs[0];
 	if (len > space) len = space;
+
 	memcpy(ptrs[0], buf, len);
 	ptrs[0] += len;
+	/* ptrs[1] is the last byte of the buffer, it must be 0.
+	 * on overflow:
+	 *   ptrs[0] + (ptrs[1] - ptrs[0]) = ptrs[1] */
+	*ptrs[0] = '\0';
+}
+
+int vsnprintf(char *restrict str, size_t len, const char *restrict fmt, va_list ap) {
+	char *ptrs[2] = {str, str + len - 1};
+	return __printf_internal(fmt, ap, backend_buf, &ptrs);
+}
+
+
+int printf(const char *restrict fmt, ...) {
+	int ret;
+	va_list argp;
+	va_start(argp, fmt);
+	ret = vprintf(fmt, argp);
+	va_end(argp);
+	return ret;
 }
 
-int snprintf(char *str, size_t len, const char *fmt, ...) {
-	int ret = 0;
-	char *ptrs[2] = {str, str + len};
+int fprintf(FILE *restrict f, const char *restrict fmt, ...) {
+	int ret;
 	va_list argp;
 	va_start(argp, fmt);
-	ret = __printf_internal(fmt, argp, backend_buf, &ptrs);
+	ret = vfprintf(f, fmt, argp);
 	va_end(argp);
-	if (ptrs[0] < ptrs[1]) *ptrs[0] = '\0';
 	return ret;
 }
 
+int snprintf(char *restrict str, size_t len, const char *restrict fmt, ...) {
+	int ret;
+	va_list argp;
+	va_start(argp, fmt);
+	ret = vsnprintf(str, len, fmt, argp);
+	va_end(argp);
+	return ret;
+}
+
+int vprintf(const char *restrict fmt, va_list ap) {
+	return vfprintf(stdout, fmt, ap);
+}
+
 int _klogf(const char *fmt, ...) {
-	// idiotic. however, this hack won't matter anyways
 	char buf[256];
-	int ret = 0;
-	char *ptrs[2] = {buf, buf + sizeof buf};
+	int ret;
 	va_list argp;
 	va_start(argp, fmt);
-	ret = __printf_internal(fmt, argp, backend_buf, &ptrs);
+	ret = vsnprintf(buf, sizeof buf, fmt, argp);
 	va_end(argp);
-	if (ptrs[0] < ptrs[1]) *ptrs[0] = '\0';
 	_syscall_debug_klog(buf, ret);
 	return ret;
 }
-- 
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