On Thu, 19 Mar 2020 16:53:32 +0800, ", Samuel" said:
> movl $0xffffe000,%ecx or 0xfffff000 for 4KB stacks
> andl %esp,%ecx
> movl %ecx,p
>
> Why is *"stack pointer(esp) & 0xffffe000"* equal to the process descriptor
> base address?
>
> That means the base address of process descriptor is always *0xXYZ...000*,
> right? It is weird.
It's not at all weird if the kernel, when allocating the stack space to begin with,
asked for 1 (or 2 contiguous) 4K chunks of memory, at a page-aligned address....
For example, see kernel/fork.c:
238 /*
239 * Allocated stacks are cached and later reused by new threads,
240 * so memcg accounting is performed manually on assigning/releasing
241 * stacks to tasks. Drop __GFP_ACCOUNT.
242 */
243 stack = __vmalloc_node_range(THREAD_SIZE, THREAD_ALIGN,
244 VMALLOC_START, VMALLOC_END,
245 THREADINFO_GFP & ~__GFP_ACCOUNT,
246 PAGE_KERNEL,
247 0, node, __builtin_return_address(0));
I'll leave figuring out what THREAD_ALIGN is set to, as an exercise for the student. :)
Attachment:
pgpIWAX6EHl96.pgp
Description: PGP signature
_______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
