更改entry.S中的system_call时发生内核恐慌
我正在尝试实现一个系统调用计数器，因此我在 task_struct 中包含了一个 int 值，以及一个在单独的文件中递增它的函数。这个函数应该在它实际调用所需的 sys_call 之前从 system_call 调用（我有理由在之前而不是之后调用它）。但是，如果我将它放在 sys_call 之前，那么在编译和启动之后会出现内核恐慌（“试图终止 init_idle”），如果我将它放在 sys_call 之后，它就会起作用。有什么区别以及如何克服这个问题？
这是相关代码
ENTRY(system_call)
pushl %eax # save orig_eax
SAVE_ALL
GET_CURRENT(%ebx)
testb $0x02,tsk_ptrace(%ebx) # PT_TRACESYS
jne tracesys
cmpl $(NR_syscalls),%eax
jae badsys
call update_counter /*This causes a kernel panic*/
call *SYMBOL_NAME(sys_call_table)(,%eax,4)
movl %eax,EAX(%esp) # save the return value
I'm trying to implement a system call counter, and as a result I included an int value in task_struct, and a function that increments it in a separate file. This function is supposed to be called from system_call right before it actually calls the required sys_call (I have my reasons to call it before and not after). However, if I place it before the sys_call then after compiling and booting there's a kernel panic ("tried to kill init_idle"), and if I place it right after the sys_call, it works. What's the difference and how do I overcome this?
Here's the relevant code
ENTRY(system_call)
pushl %eax # save orig_eax
SAVE_ALL
GET_CURRENT(%ebx)
testb $0x02,tsk_ptrace(%ebx) # PT_TRACESYS
jne tracesys
cmpl $(NR_syscalls),%eax
jae badsys
call update_counter /*This causes a kernel panic*/
call *SYMBOL_NAME(sys_call_table)(,%eax,4)
movl %eax,EAX(%esp) # save the return value
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我猜想
%eax会因调用update_counter而被丢弃。特别是，如果这是一个 C 函数（而不是手写汇编），那么调用约定意味着它几乎肯定会被更改：%eax被定义为返回结果（或其一部分） ，或者（在其他情况下，例如返回void的函数）可供被调用者自由使用而不保留它。尝试：
I would guess that
%eaxis being trashed by the call toupdate_counter. In particular, if that's a C function (rather than handwritten assembly), then the calling conventions mean that it will almost certainly be changed:%eaxis defined to either return the result (or part of it), or (in other cases, such as a function returningvoid) be free for the callee to use without preserving it.Try: