Page fault handler causes read data to be corrupt?
Posted: Thu Dec 28, 2017 10:12 am
It seems after I map a page in my page fault handler, the data at the paged address is corrupt on the first read, but fine on the second.
Here is my page fault handler:
The signature for pg_fault in C:
Currently, when pg_fault is called, it identity maps the page that isn't present. It's a temporary solution so I can read ACPI tables while paging.
I have a test that shows that shows the Length field in the RSDT table:
The first try triggers a page fault, which identity maps the page. The first read attempt returns something resembling a real mode address in the ROM (like a vector in the IVT). The second try returns the correct value. I would expect both of these to be the same. It even reads fine in the page handler right after reloading CR3 and calling INVLPG on the address. I'm pretty sure there is something wrong with my assembly page fault handler, but I can't tell what it is. I'm using Virtualbox 4.3.10.
Here is my page fault handler:
Code: Select all
.globl exception_page_fault
.align 4
exception_page_fault:
cld
push %esp
call pg_fault
add $0x08,%esp # 4 bytes for error code, 4 bytes for saved ESP
iret
Code: Select all
void pg_fault(uint32_t esp, uint32_t ec); // esp = ESP upon entry to fault handler; ec = error codeI have a test that shows that shows the Length field in the RSDT table:
Code: Select all
printf("first try: %u\n", acpi_rsdt->length);
printf("second try: %u\n", acpi_rsdt->length);