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Octocontrabass wrote:You are missing some of the required knowledge.

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  pusha
  pop eax

What does this code do?

iansjack wrote:So you push all registers, pop what was in edi into edx, call some routine then do an interrupt return without restoring the stack. Under these conditions a crash is expected behaviour.

page_fault:
  ;save error code from stack
  pop eax
  push eax
  pusha
  call page_fault_handler
  popa
  iret

void page_fault_exception() {
    serial_printf("page_fault_exception!\n");
    uint32_t error_code = 0;
    __asm__ volatile ("mov %%eax, %0" : "=r"(error_code));
    . . .
}

iansjack wrote:The code is nearly correct, but it clobbers the eax register, and it doesn't remove the error code from the stack.

If you wish to preserve the value of eax you should push all registers then read the value of the error code directly from the appropriate position on the stack. Remember that the stack is just a series of memory locations so you can read/write its values directly (with an offset[%esp] instruction) instead of using pop/push. Also, remember to remove the error code from the stack before you return from the interrupt.

page_fault:
  ;save error code from stack to eax
  pop eax
  ;return error code to stack
  push eax
  ;save all 32bit registers
  pushad
  call page_fault_handler
  ;return all 32bit registers
  popad
  iretd

nexos wrote:My ISR stub looks like:

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    cli
    push byte 14
    pushad
    mov ax, 0x10
    mov ds, ax
    mov es, ax
    mov fs, ax
    mov gs, ax
    mov eax, esp
    push eax
    mov eax, HalIsrHandler
    call eax
    pop eax
    popad
    add esp, 8
    sti
    iretd

Note that it passes the structure as a pointer. It cleans up the error code and interrupt number by adding 8 to esp. The D isn't necessary. NASM will translate. (It won't in 64 bit mode, but that is irrelevant.) I include the D for verbosity's purposes.

page_fault:
  cli
  ;save error code from stack to eax
  pop eax
  ;return error code to stack
  push eax
  ;save all 32bit registers
  pushad
  call page_fault_handler
  ;return all 32bit registers
  popad
  ;delete error code from stack
  add esp, 4
  sti
  iretd

nexos wrote:Yes, that looks good. Are using the registers as a structure in your C handler? If so, then it is good idea to pass the structure by pointer. Right before you call the function, you would do something like this

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mov eax, esp
push eax

mrjbom wrote:Is that correct?

nexos wrote:

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mov eax, esp
push eax

push esp

Octocontrabass wrote:

mrjbom wrote:Is that correct?

No. You're still clobbering EAX. If you want to pass the error code to the function you're calling in a register, you need to read it from the stack after PUSHAD, using an instruction like "mov eax, [esp+32]"

page_fault:
  cli
  ;save all 32bit registers
  pushad
  ;save error code from stack to eax
  mov eax, [esp + 4]
  call page_fault_handler
  ;return all 32bit registers
  popad
  ;delete error code from stack
  add esp, 4
  sti
  iretd

nexos wrote:push eax directly before the calling the function and all should be well. The ABI requires parameters to be passed on the stack.

page_fault:
  cli
  pushad
  ;save error code from stack to eax
  mov eax, [esp + 4]
  push eax
  call page_fault_handler
  ;return all 32bit registers
  popad
  ;delete error code from stack
  add esp, 4
  sti
  iretd