Adding a file reading example

examples/linux64/file-reading/Makefile

@@ -0,0 +1,15 @@
+# One can run this file inside this folder as $make clean && make all
+
+CC = python -m ppci cc --freestanding -I ../../../librt/libc/include
+CFLAGS = -O1
+
+all: reading_file
+
+reading_file: reading_file.o
+	python -m ppci ld --entry main --layout ../linux64.mmap $^ -o $@
+
+reading_file.o:
+	$(CC) reading_file.c ../../../librt/libc/src/*.c ../../../librt/libc/src/*/*.c  -o reading_file.o
+
+clean:
+	rm -f *.o *.S reading_file

examples/linux64/file-reading/example.txt

@@ -0,0 +1,6 @@
+The PPCI (Pure Python Compiler Infrastructure) project is a compiler
+written entirely in the Python programming
+language. It contains front-ends for various programming languages as
+well as machine code generation functionality. With this library you can
+generate (working!) machine code using Python (and thus very easy to
+explore, extend, etc.)!

examples/linux64/file-reading/reading_file.c

@@ -0,0 +1,48 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/stat.h> 
+
+// In this example we will be using some low level functions to open, read and close a file from the system
+
+int main(int argc, char **argv){
+    // The function open and the flag O_RDONLY are defined in fcntl.h
+    // It is a thin wrapper around a bare syscall
+    int fd = open("example.txt",O_RDONLY);
+
+    if (fd == -1){
+		printf("ERROR: Could not open the file");
+		exit(1);
+	}
+
+    // f_size is a helper function defined in sys/stat.h for this libc
+    // It is a wrapper around the fstat syscall to get the size in bytes of the file
+    long buffer_size = f_size(fd);
+
+    if (buffer_size == -1){
+		printf("Error while getting the file size");
+		exit(1);
+	}
+
+    // Malloc also uses syscalls to get memory from the system
+    void *buffer = malloc(buffer_size);
+
+    // Both read and close are defined in unistd.h
+    // Both are wrappers around bare syscalls
+    ssize_t size = read(fd, buffer, (size_t)buffer_size);
+
+    if (size == -1){
+		printf("Error while reading file to buffer");
+		exit(1);
+	}
+
+    if (close(fd) == -1){
+        printf("Error while closing the file");
+		exit(1);
+    }
+
+    printf("%s",(char*)buffer);
+
+    exit(0);
+}

librt/libc/include/fcntl.h

@@ -0,0 +1,6 @@
+#define	O_RDONLY	0x0000		/* open for reading only */
+#define	O_WRONLY	0x0001		/* open for writing only */
+#define	O_RDWR		0x0002		/* open for reading and writing */
+#define	O_ACCMODE	0x0003		/* mask for above modes */
+
+int open(const char *filename, int mode);

librt/libc/include/stddef.h

@@ -4,7 +4,8 @@
 
 
 typedef int wchar_t;
-typedef int size_t;
+typedef unsigned int size_t;
+typedef int ssize_t;
 
 #define offsetof(TYPE, MEMBER) __builtin_offsetof(TYPE, MEMBER)
 

librt/libc/include/sys/stat.h

@@ -0,0 +1,3 @@
+void fstat(int fd, void * statstruct);
+
+inline int f_size(int fd);

librt/libc/include/unistd.h

@@ -8,5 +8,10 @@ int isatty(int fd);
 char *getcwd(char *buf, size_t size);
 char *getwd(char *buf);
 
+ssize_t read(int, void *, size_t);
+ssize_t write(int, const void *, size_t);
+
+int close(int);
+
 #endif
 

librt/libc/src/fcntl.c

@@ -0,0 +1,6 @@
+#include "stdlib.h"
+#include "fcntl.h"
+
+int open(const char *filename, int mode){
+	return syscall(2, filename, mode, 0);
+}

librt/libc/src/stat.c

@@ -0,0 +1,22 @@
+#include "stdlib.h"
+#include "sys/stat.h"
+
+void fstat(int fd, void * statstruct){
+    syscall(5, fd, (long) statstruct, 0);
+}
+
+inline int f_size(int fd){
+	// needs to inform the size of kernel linux stat struct size
+	// which is 144 bytes in x86_64 systems
+    char buffer[144];
+
+    void * statstruct = (void*)(&buffer);
+
+    fstat(fd, statstruct);
+
+    // from the begin to the size part, we have 
+	// 8 + 8 + 8 + 8 + 4 + 4 + 8 = 48 bytes
+	long size = *((long*)(statstruct + 48));
+
+    return size;
+}

librt/libc/src/unistd.c

@@ -0,0 +1,10 @@
+#include "stdlib.h"
+#include "unistd.h"
+
+ssize_t read(int fd, void *buf, size_t count){
+	return (size_t) syscall(0, fd, buf, count);
+}
+
+int close(int fd){
+    return syscall(3, fd, 0, 0);
+}