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. :)
pgpenw8_Tz43H.pgp
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