From c830b365f52bdd8dcaab604614658ce70d158055 Mon Sep 17 00:00:00 2001
From: FreeArtMan <dos21h@gmail.com>
Date: Fri, 12 Aug 2022 18:02:51 +0100
Subject: Add syscalls

---
 md/notes/undefined_c/titles.md | 79 +++++++++++++++++++++++++++++++++++++-----
 1 file changed, 70 insertions(+), 9 deletions(-)

(limited to 'md/notes')

diff --git a/md/notes/undefined_c/titles.md b/md/notes/undefined_c/titles.md
index 7753e65..513b533 100644
--- a/md/notes/undefined_c/titles.md
+++ b/md/notes/undefined_c/titles.md
@@ -635,6 +635,9 @@ So now executable runs libshare from local directory. Ofc there is possible to i
 
 ### Static library
 
+
+
+
 ### Static binary
 
 Static binary don't use any shared libraries, and its possible to built it once and distribute on other platforms
@@ -676,33 +679,91 @@ $ ldd static_elf
 Statically compiled file should work on most platforms.
 
 
+<!--
+### stdin,stdout,stderr
+### Styles
+--->
 
-### Dynamic binary
 
-Dynamic binary is required to load dynamically linked libraries, they must be in known location.
 
-Replacing dynamic libraries with your own
 
+## Basic usage
 
+### File manipulation with libc
 
-Point to custom location of dynamic library
+Create file open data using libc functions
 
+```c
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
 
+int main() {
+	FILE *f = fopen("file.txt","w+");
+	char *s = "Hello";
+	fwrite(s,1,strlen(s),f);
+	fclose(f);
+}
+```
 
+Open file and read data back
 
-### stdin,stdout,stderr
+```c
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
 
+int main() {
+	FILE *f = fopen("file.txt","r");
+	char buf[128];
+	int r;
+	r = fread(buf,1,128,f);
+	buf[r] = 0;
+	printf("->%s\n",buf,r);
+	fclose(f);
+}
+```
 
-### Styles
+### File manipulation with syscalls
 
+Now lets do the same without using libc functions using syscall function to directly use syscalls,
+its also straightforward to rewrite example for assembly.
 
+```c
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/syscall.h>
+#include <string.h>
 
+int main(void) {
+  int fd = syscall(SYS_open, "sys.txt", O_CREAT|O_WRONLY, S_IRWXU|S_IRGRP|S_IXGRP);
+  char s[] = "hello sycall\n";
+  syscall(SYS_write, fd, s, strlen(s));
+  syscall(SYS_close, fd);
+  return 0;
+}
+```
 
 
-## Basic usage
+Read data from file
+
+```c
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/syscall.h>
+#include <string.h>
+
+int main(void) {
+  int fd = syscall(SYS_open, "sys.txt", O_RDONLY);
+  char s[128];
+  int r = syscall(SYS_read, fd, s, 128);
+  s[r] = 0;
+  syscall(SYS_close, fd);
+  syscall(SYS_write, 0, s, r);
+  return 0;
+}
+```
 
-### File manipulation with libc
-### File manipulation with syscalls
 
 ## Base usage
 
-- 
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