关于linux：如何理解“/ proc / [pid] / stack”？

How to understand “/proc/[pid]/stack”?

根据proc手册：

/proc/[pid]/stack (since Linux 2.6.29)

This file provides a symbolic trace of the function calls in
this process's kernel stack. This file is provided only if
the kernel was built with the CONFIG_STACKTRACE configuration
option.

所以我写了一个测试程序：

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#include <stdio.h>
#include <sys/wait.h>
#include <unistd.h>
#include <pthread.h>

void *thread_func(void *p_arg)
{
pid_t pid = fork();
if (pid > 0) {
wait(NULL);
return 0;
} else if (pid == 0) {
sleep(1000);
return 0;
}
return NULL;
}
int main(void)
{
pthread_t t1, t2;

pthread_create(&t1, NULL, thread_func,"Thread 1");
pthread_create(&t2, NULL, thread_func,"Thread 2");

sleep(1000);
return 0;
}

运行后，使用pstack检查进度的线程：

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linux-uibj:~ # pstack 24976
Thread 3 (Thread 0x7fd6e4ed5700 (LWP 24977)):
#0 0x00007fd6e528d3f4 in wait () from /lib64/libpthread.so.0
#1 0x0000000000400744 in thread_func ()
#2 0x00007fd6e52860a4 in start_thread () from /lib64/libpthread.so.0
#3 0x00007fd6e4fbb7fd in clone () from /lib64/libc.so.6
Thread 2 (Thread 0x7fd6e46d4700 (LWP 24978)):
#0 0x00007fd6e528d3f4 in wait () from /lib64/libpthread.so.0
#1 0x0000000000400744 in thread_func ()
#2 0x00007fd6e52860a4 in start_thread () from /lib64/libpthread.so.0
#3 0x00007fd6e4fbb7fd in clone () from /lib64/libc.so.6
Thread 1 (Thread 0x7fd6e569f700 (LWP 24976)):
#0 0x00007fd6e4f8d6cd in nanosleep () from /lib64/libc.so.6
#1 0x00007fd6e4f8d564 in sleep () from /lib64/libc.so.6
#2 0x00000000004007b1 in main ()

同时，检查/proc/24976/stack：

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linux-uibj:~ # cat /proc/24976/stack
[<ffffffff804ba1a7>] system_call_fastpath+0x16/0x1b
[<00007fd6e4f8d6cd>] 0x7fd6e4f8d6cd
[<ffffffffffffffff>] 0xffffffffffffffff

24976进程有3个线程，它们都在系统调用(nanosleep和wait)上阻塞，因此所有3线程现在都在kernel空间中工作，现在转为内核线程，对？如果是这样，/proc/[pid]/stack文件中应该有3个堆栈。但似乎/proc/[pid]/stack文件中只有1堆栈。

我应该如何理解/proc/[pid]/stack？

How should I understand /proc/[pid]/stack ?

摘自proc的手册页：

There are additional helpful pseudo-paths:

[stack]
The initial process's (also known as the main thread's) stack.

在这之下，您可以找到：

[stack:[tid]] (since Linux 3.4)

A thread's stack (where the [tid] is a thread ID).
It corresponds to the /proc/[pid]/task/[tid]/path.

这似乎是你在寻找什么。