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/*
* minimal freestanding C library
*
* works for IA-32 and Linux, uses old INT 80h software interrupts
* for system calls.
*
*/
int strlen( char *s )
{
char *p;
p = s;
while( *p != '\0' ) {
p++;
}
return p - s;
}
enum {
EXIT_SUCCESS = 0,
EXIT_FAILURE = 1
};
enum {
SYSCALL_EXIT = 1,
SYSCALL_READ = 3,
SYSCALL_WRITE = 4
};
int errno;
static __attribute__((noinline)) int syscall1( int id, int arg0 )
{
int retval;
__asm__ volatile( "\
push %%ebx\n\
mov %1, %%eax\n\
mov %2, %%ebx\n\
int $0x80\n\
mov %%eax, %0\n\
pop %%ebx\n" : "=m"( retval ) : "m"( id ), "m"( arg0 )
: "eax", "ebx" );
if( retval < 0 ) {
errno = -retval;
return -1;
}
return retval;
}
static __attribute__((noinline)) int syscall3( int id, int arg0, int arg1, int arg2 )
{
int retval;
__asm__ volatile( "\
push %%ebx\n\
push %%ecx\n\
push %%edx\n\
mov %1, %%eax\n\
mov %2, %%ebx\n\
mov %3, %%ecx\n\
mov %4, %%edx\n\
int $0x80\n\
mov %%eax, %0\n\
pop %%edx\n\
pop %%ecx\n\
pop %%ebx\n" : "=m"( retval ) : "m"( id ), "m"( arg0 ), "m"( arg1 ), "m"( arg2 )
: "eax", "ebx", "ecx", "edx" );
if( retval < 0 ) {
errno = -retval;
return -1;
}
return retval;
}
enum {
STDIN_FILENO = 0,
STDOUT_FILENO = 1,
STDERR_FILENO = 2
};
static void print_char( int fd, int c )
{
char s[1];
s[0] = c;
syscall3( SYSCALL_WRITE, fd, (int)s, 1 );
}
static void print_string( char *s )
{
syscall3( SYSCALL_WRITE, STDOUT_FILENO, (int)s, strlen( s ) );
}
static void print_newline( void )
{
print_char( STDOUT_FILENO, '\n' );
}
static int read_string( int fd, char *buf, int size )
{
return syscall3( SYSCALL_READ, fd, (int)buf, size );
}
enum {
EOF = -1
};
int puts( char *s )
{
print_string( s );
print_newline( );
return 1;
}
int getchar( )
{
int res;
char buf[1];
res = read_string( STDIN_FILENO, buf, 1 );
if( res == 0 ) {
return EOF;
}
return buf[0];
}
int putchar( int c )
{
print_char( STDOUT_FILENO, c );
return c;
}
void exit( int status )
{
syscall1( SYSCALL_EXIT, status );
}
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