在C中，除了使用#define val之外，不能更改struct属性
在Minix 3.1.2a中，我有一个结构“ struct proc ”，其中存储了任何进程的PCB，但是在下面的代码p_currenthash新属性“ p_currenthash ”添加到此结构时我遇到了问题。 除了使用#define指令定义的常量外，我无法更改其值; 否则，系统停止响应。 为清楚起见，这里是结构：
struct proc { struct stackframe_s p_reg; /* process' registers saved in stack frame */ #if (CHIP == INTEL) reg_t p_ldt_sel; /* selector in gdt with ldt base and limit */ struct segdesc_s p_ldt[2+NR_REMOTE_SEGS]; /* CS, DS and remote segments */ #endif #if (CHIP == M68000) /* M68000 specific registers and FPU details go here. */ #endif proc_nr_t p_nr; /* number of this process (for fast access) */ struct priv *p_priv; /* system privileges structure */ short p_rts_flags; /* process is runnable only if zero */ short p_misc_flags; /* flags that do suspend the process */ char p_priority; /* current scheduling priority */ char p_max_priority; /* maximum scheduling priority */ char p_ticks_left; /* number of scheduling ticks left */ char p_quantum_size; /* quantum size in ticks */ struct mem_map p_memmap[NR_LOCAL_SEGS]; /* memory map (T, D, S) */ clock_t p_user_time; /* user time in ticks */ clock_t p_sys_time; /* sys time in ticks */ struct proc *p_nextready; /* pointer to next ready process */ struct proc *p_caller_q; /* head of list of procs wishing to send */ struct proc *p_q_link; /* link to next proc wishing to send */ message *p_messbuf; /* pointer to passed message buffer */ int p_getfrom_e; /* from whom does process want to receive? */ int p_sendto_e; /* to whom does process want to send? */ sigset_t p_pending; /* bit map for pending kernel signals */ char p_name[P_NAME_LEN]; /* name of the process, including \0 */ int p_endpoint; /* endpoint number, generation-aware */ #if DEBUG_SCHED_CHECK int p_ready, p_found; #endif char p_currenthash; /* hash */ };
现在，假设我想设置它的值。 最初我使用下面定义的常量。
#define NONE -1 register struct proc *rp; rp->p_currenthash=NONE;
这很好，但是这个： rp->p_currenthash=0 ; 将导致程序停止响应。
任何建议将不胜感激
这是main()的主要初始化：
/* Start the ball rolling. */ struct boot_image *ip; /* boot image pointer */ register struct proc *rp; /* process pointer */ register struct priv *sp; /* privilege structure pointer */ register int i, s; int hdrindex; /* index to array of a.out headers */ phys_clicks text_base; vir_clicks text_clicks, data_clicks; reg_t ktsb; /* kernel task stack base */ struct exec e_hdr; /* for a copy of an a.out header */ /* Initialize the interrupt controller. */ intr_init(1); /* Clear the process table. Anounce each slot as empty and set up mappings * for proc_addr() and proc_nr() macros. Do the same for the table with * privilege structures for the system processes. */ for (rp = BEG_PROC_ADDR, i = -NR_TASKS; rp p_rts_flags = SLOT_FREE; /* initialize free slot */ rp->p_nr = i; /* proc number from ptr */ rp->p_currenthash=NONE; rp->p_endpoint = _ENDPOINT(0, rp->p_nr); /* generation no. 0 */ (pproc_addr + NR_TASKS)[i] = rp; /* proc ptr from number */ } for (sp = BEG_PRIV_ADDR, i = 0; sp s_proc_nr = NONE; /* initialize as free */ sp->s_id = i; /* priv structure index */ ppriv_addr[i] = sp; /* priv ptr from number */ } /* Set up proc table entries for processes in boot image. The stacks of the * kernel tasks are initialized to an array in data space. The stacks * of the servers have been added to the data segment by the monitor, so * the stack pointer is set to the end of the data segment. All the * processes are in low memory on the 8086. On the 386 only the kernel * is in low memory, the rest is loaded in extended memory. */ /* Task stacks. */ ktsb = (reg_t) t_stack; for (i=0; i proc_nr); /* get process pointer */ ip->endpoint = rp->p_endpoint; /* ipc endpoint */ rp->p_max_priority = ip->priority; /* max scheduling priority */ rp->p_priority = ip->priority; /* current priority */ rp->p_quantum_size = ip->quantum; /* quantum size in ticks */ rp->p_ticks_left = ip->quantum; /* current credit */ strncpy(rp->p_name, ip->proc_name, P_NAME_LEN); /* set process name */ (void) get_priv(rp, (ip->flags & SYS_PROC)); /* assign structure */ priv(rp)->s_flags = ip->flags; /* process flags */ priv(rp)->s_trap_mask = ip->trap_mask; /* allowed traps */ priv(rp)->s_call_mask = ip->call_mask; /* kernel call mask */ priv(rp)->s_ipc_to.chunk[0] = ip->ipc_to; /* restrict targets */ if (iskerneln(proc_nr(rp))) { /* part of the kernel? */ if (ip->stksize > 0) { /* HARDWARE stack size is 0 */ rp->p_priv->s_stack_guard = (reg_t *) ktsb; *rp->p_priv->s_stack_guard = STACK_GUARD; } ktsb += ip->stksize; /* point to high end of stack */ rp->p_reg.sp = ktsb; /* this task's initial stack ptr */ text_base = kinfo.code_base >> CLICK_SHIFT; /* processes that are in the kernel */ hdrindex = 0; /* all use the first a.out header */ } else { hdrindex = 1 + i-NR_TASKS; /* servers, drivers, INIT */ } /* The bootstrap loader created an array of the a.out headers at * absolute address 'aout'. Get one element to e_hdr. */ phys_copy(aout + hdrindex * A_MINHDR, vir2phys(&e_hdr), (phys_bytes) A_MINHDR); /* Convert addresses to clicks and build process memory map */ text_base = e_hdr.a_syms >> CLICK_SHIFT; text_clicks = (e_hdr.a_text + CLICK_SIZE-1) >> CLICK_SHIFT; if (!(e_hdr.a_flags & A_SEP)) text_clicks = 0; /* common I&D */ data_clicks = (e_hdr.a_total + CLICK_SIZE-1) >> CLICK_SHIFT; rp->p_memmap[T].mem_phys = text_base; rp->p_memmap[T].mem_len = text_clicks; rp->p_memmap[D].mem_phys = text_base + text_clicks; rp->p_memmap[D].mem_len = data_clicks; rp->p_memmap[S].mem_phys = text_base + text_clicks + data_clicks; rp->p_memmap[S].mem_vir = data_clicks; /* empty - stack is in data */ /* Set initial register values. The processor status word for tasks * is different from that of other processes because tasks can * access I/O; this is not allowed to less-privileged processes */ rp->p_reg.pc = (reg_t) ip->initial_pc; rp->p_reg.psw = (iskernelp(rp)) ? INIT_TASK_PSW : INIT_PSW; /* Initialize the server stack pointer. Take it down one word * to give crtso.s something to use as "argc". */ if (isusern(proc_nr(rp))) { /* user-space process? */ rp->p_reg.sp = (rp->p_memmap[S].mem_vir + rp->p_memmap[S].mem_len) <p_reg.sp -= sizeof(reg_t); } /* Set ready. The HARDWARE task is never ready. */ if (rp->p_nr != HARDWARE) { rp->p_rts_flags = 0; /* runnable if no flags */ lock_enqueue(rp); /* add to scheduling queues */ } else { rp->p_rts_flags = NO_MAP; /* prevent from running */ } /* Code and data segments must be allocated in protected mode. */ alloc_segments(rp); }
register struct proc *rp; rp->p_currenthash=NONE;
rp是一个未初始化的指针; 它没有指向有效的struct proc对象，因此取消引用它会导致未定义的行为 。 分配-1时这并没有崩溃的事实是纯粹的运气。 （运气不好，因为它误导你相信你正在做一些有意义的事情）
实际上问题没有解决，首先在主要内容中初始化“ p_currenthash ”，如上所示，稍后在一个名为pic_proc的函数中，我有这样的代码：
register struct proc **xpp; /* iterate over queue */ register struct proc *rp; /* process to run */ int q; for (q=0; q < NR_SCHED_QUEUES; q++) { if ( (rp = rdy_head[q]) != NIL_PROC) { for (xpp = &rdy_head[q]; *xpp != NIL_PROC; xpp = &(*xpp)->p_nextready) { if ((*xpp)->p_currenthash==NONE) { pick_val++; } } } }
该代码工作正常，如果我改变了属性“p_currenthash”，如果发生了如下问题：
register struct proc **xpp; /* iterate over queue */ register struct proc *rp; /* process to run */ int q; for (q=0; q < NR_SCHED_QUEUES; q++) { if ( (rp = rdy_head[q]) != NIL_PROC) { for (xpp = &rdy_head[q]; *xpp != NIL_PROC; xpp = &(*xpp)->p_nextready) { if ((*xpp)->p_currenthash==NONE) { pick_val++; (*xpp)->p_currenthash=1; } } } }
我真的无法实现这个问题。