rts.c

一个编译器修改的例子

#include <stdio.h>
#include <string.h>

#include "rts.h"

/* This is part of the runtime system. It is linked with the C code
 * the compiler produces when compiling Asterix source. It is not part
 * of the compiler itself.
 */

void runtime_error(const char *msg)
{
    fprintf(stderr, "Runtime error: %s\n", msg);
    exit(1);
}


array new_array(int size, size_t bytes_per_element)
{
    array  a;
    size_t total_bytes;

    if (size < 0)
	runtime_error("creating array with negative size");

    /* Koen: due to (weird) alignment rules the array header is NOT equal
     * to sizeof(a->size); there may be a gap between size and the data!
     */
    total_bytes = sizeof(*a)-sizeof(a->data) + size * bytes_per_element;
    a		= calloc(total_bytes, 1);

    if (a == 0)
	runtime_error("out of memory");

    a->size = size;
    return a;
}


array string_const(int size, const char *str)
{
    array a    = new_array( size, 1);

    memcpy(a->data.c, str, size);

    return a;
}


void delete_array(array a)
{
    free(a);
}


void *array_index(array a, size_t bytes_per_element, int index)
{
    if (a == 0)
	runtime_error("indexing null reference");

    /* Koen: new test for robustness avoids casting to unsiged
     */
    if (index < 0 || a->size <= index)
	runtime_error("out of bound indexing");

    return (char *) &a->data + index * bytes_per_element;
}

/* Koen: runtime check for null references requires additional code
 */
int array_size(array a)
{
    if (a == 0)
	runtime_error("taking the size of a null reference");

    return a->size;
}


int main(int argc, char **argv)
{
    extern int cb_main(array);

    int   i, ret_val;
    array new_argv = new_array(argc, sizeof(array));

    /* Koen: allocate I/O buffer for reporting runtime
     * errors BEFORE running out of memory
     */
    fprintf( stderr, "%s", "");

    for (i = 0; i < argc; i ++)
    {
	array *next_arg_adr = array_index(new_argv, sizeof(array), i);

	/* Koen: removed redundant copy
	 */
	*next_arg_adr = string_const(strlen(argv [i]), argv [i]);
    }

    for (i = 0; strings [i].c != 0; i ++)
	strings [i].a = string_const(strings [i].s, strings [i].c);

    ret_val = cb_main(new_argv);


    for (i = 0; strings [i].a != 0; i ++)
	free(strings [i].a);

    for (i = 0; i < argc; i ++)
	delete_array(* (array *) array_index(new_argv, sizeof(array), i));

    delete_array(new_argv);

    return ret_val;
}