Method alloc

src/e9patch/e9misc.cpp:77–100

* Instruction set allocate. */

 * Instruction set allocate.
 */
void *InstrSet::alloc()
{
    lb--;
    Instr *I = lb;
    Instr *S = I - 1;

    if ((void *)S < limit)
    {
        intptr_t base = (uintptr_t)limit;
        extend = (extend >= 256? 256: 2 * extend);
        base -= extend * PAGE_SIZE;
        errno = 0;
        void *ptr =
            mmap((void *)base, extend * PAGE_SIZE, PROT_READ | PROT_WRITE,
            MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE, -1, 0);
        if (ptr != (void *)base && errno != 0)
            error("failed to extend instruction buffer: %s", strerror(errno));
        if (ptr != (void *)base && errno == 0)
            error("failed to extend instruction buffer; expected %p, got %p",
                (void *)base, ptr);
        limit = ptr;
    }
    return (void *)I;
}

/*
 * Find the first instruction >= the offset.