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Fix Bug: Grow stack if necessary in case of a page fault in the kernel context

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This commit is contained in:
sBubshait
2024-12-05 01:15:46 +00:00
parent f171a05108
commit 52ec8fe779
1 changed files with 21 additions and 18 deletions
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39
src/userprog/exception.c
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@@ -157,30 +157,33 @@ page_fault (struct intr_frame *f)
write = (f->error_code & PF_W) != 0;
user = (f->error_code & PF_U) != 0;
if (!user || !not_present)
/* Select the appropriate stack pointer based on the context of the fault. */
void *esp = user ? f->esp : thread_current()->curr_esp;
/* If the fault address is in a user page that is not present, then it might
be just that the stack needs to grow or that it needs to be lazily loaded.
So we attempt to grow the stack. If this does not work, we check our SPT to
see if the page is expected to have data loaded in memory. */
void *upage = pg_round_down (fault_addr);
if (not_present && is_user_vaddr (upage) && upage != NULL)
{
if (is_valid_stack_access (fault_addr, esp))
if (grow_stack (upage))
return;
if (try_fetch_page (upage, write))
return;
}
/* If the page fault occurred in kernel mode, then we intentionally indicate
a fault (for get_user() etc). */
if (!user)
{
f->eip = (void *)f->eax;
f->eax = 0xffffffff;
return;
}
/* If the fault address is in a user page that is not present, then it might
be just that the stack needs to grow or that it needs to be lazily loaded.
So we attempt to grow the stack. If this does not work, we check our SPT to see if the page
is expected to have data loaded in memory. */
void *upage = pg_round_down (fault_addr);
if (not_present && is_user_vaddr (upage) && upage != NULL)
{
if (is_valid_stack_access (fault_addr, f->esp))
{
if (grow_stack (upage))
return;
}
if (try_fetch_page (upage, write))
return;
}
/* To implement virtual memory, delete the rest of the function
body, and replace it with code that brings in the page to
which fault_addr refers. */