tinyos

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I tried allocating 4K on userspace stack and noticed that the kernel crashes hard. You can see the issue if you update the new user/utils/pwd.c to look like this:

penberg@jaguar:~/src/tinyos$ git diff diff --git a/user/utils/pwd.c b/user/utils/pwd.c index 53aee22..3c46b49 100644 --- a/user/utils/pwd.c +++ b/user/utils/pwd.c @@ -1,10 +1,10 @@ #include <ulib.h>

#define BUF_SIZE 4096 -static char buf[BUF_SIZE];

int main(int argc, char **argv) {

•   char buf[BUF_SIZE];
    char *cwd;
  
    cwd = getcwd(buf, BUF_SIZE);
  

Hi, penberg It only allocs one page(just 4KB) as userspace stack in sys_execute()->task_execute()->execute_argument() and the page is mapped on userspace address USER_STACK(3GB - 4KB - 4KB), so if we alloc 4KB or larger on userspace stack, it will trigger pagefault. Here is userspace memory map:

---

• kernel space ---------------------- 0xc000 0000

• 4KB hole ---------------------- 0xbfff f000

• user stack ---------------------- 0xbfff e000

• other parts ---------------------- 0x000 0000

  I think there are two solutions:

• alloc enough user space stack in sys_execute() I am now busy at college final exam, so I may not submit new patch in time :"(

• just use global defined data: 'static char buf[..]' or 'char buf[..]' Because tinyos doesnt provide brk/sbrk and malloc() now, we need manage the memory manually.) When I use global defined 'static char buf[4MB]', it triggers a pagefault panic. The new patch 'Fix bug: map wrong userspace virtual address in map_userspace()' for this panic has been commited.

  Thanks, Xiaochen