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ISR Problem https://forum.osdev.org/viewtopic.php?f=1&t=32614 |
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Author: | zvoncika [ Sun Dec 03, 2017 2:32 am ] |
Post subject: | ISR Problem |
Hey everybody! I've been trying to implement ISR for some time now. I've been following Bran's Kernel Development tutorials. After calling my isr_install() function, I divide by zero expecting the fault handler to be called. But somehow, the system doesn't crash nor does it print anything. Any idea what it might be? EDIT: When I manually call the interrupt it works... Code: asm volatile("int $0");
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Author: | Haoud [ Sun Dec 03, 2017 2:55 am ] |
Post subject: | Re: ISR Problem |
Your compiler can optimize something and break your divide by zero code. Try to do a divide by zero in a volatile asm block Code: asm volatile("Insert code here"); Can you show you code ? |
Author: | zvoncika [ Sun Dec 03, 2017 3:13 am ] |
Post subject: | Re: ISR Problem |
Sure! Here's asm Code: global _isr0 global _isr1 global _isr2 global _isr3 global _isr4 global _isr5 global _isr6 global _isr7 global _isr8 global _isr9 global _isr10 global _isr11 global _isr12 global _isr13 global _isr14 global _isr15 global _isr16 global _isr17 global _isr18 global _isr19 global _isr20 global _isr21 global _isr22 global _isr23 global _isr24 global _isr25 global _isr26 global _isr27 global _isr28 global _isr29 global _isr30 global _isr31 ; 0: Divide By Zero Exception _isr0: cli push byte 0 push byte 0 jmp isr_common_stub ; 1: Debug Exception _isr1: cli push byte 0 push byte 1 jmp isr_common_stub ; 2: Non Maskable Interrupt Exception _isr2: cli push byte 0 push byte 2 jmp isr_common_stub ; 3: Int 3 Exception _isr3: cli push byte 0 push byte 3 jmp isr_common_stub ; 4: INTO Exception _isr4: cli push byte 0 push byte 4 jmp isr_common_stub ; 5: Out of Bounds Exception _isr5: cli push byte 0 push byte 5 jmp isr_common_stub ; 6: Invalid Opcode Exception _isr6: cli push byte 0 push byte 6 jmp isr_common_stub ; 7: Coprocessor Not Available Exception _isr7: cli push byte 0 push byte 7 jmp isr_common_stub ; 8: Double Fault Exception (With Error Code!) _isr8: cli push byte 8 jmp isr_common_stub ; 9: Coprocessor Segment Overrun Exception _isr9: cli push byte 0 push byte 9 jmp isr_common_stub ; 10: Bad TSS Exception (With Error Code!) _isr10: cli push byte 10 jmp isr_common_stub ; 11: Segment Not Present Exception (With Error Code!) _isr11: cli push byte 11 jmp isr_common_stub ; 12: Stack Fault Exception (With Error Code!) _isr12: cli push byte 12 jmp isr_common_stub ; 13: General Protection Fault Exception (With Error Code!) _isr13: cli push byte 13 jmp isr_common_stub ; 14: Page Fault Exception (With Error Code!) _isr14: cli push byte 14 jmp isr_common_stub ; 15: Reserved Exception _isr15: cli push byte 0 push byte 15 jmp isr_common_stub ; 16: Floating Point Exception _isr16: cli push byte 0 push byte 16 jmp isr_common_stub ; 17: Alignment Check Exception _isr17: cli push byte 0 push byte 17 jmp isr_common_stub ; 18: Machine Check Exception _isr18: cli push byte 0 push byte 18 jmp isr_common_stub ; 19: Reserved _isr19: cli push byte 0 push byte 19 jmp isr_common_stub ; 20: Reserved _isr20: cli push byte 0 push byte 20 jmp isr_common_stub ; 21: Reserved _isr21: cli push byte 0 push byte 21 jmp isr_common_stub ; 22: Reserved _isr22: cli push byte 0 push byte 22 jmp isr_common_stub ; 23: Reserved _isr23: cli push byte 0 push byte 23 jmp isr_common_stub ; 24: Reserved _isr24: cli push byte 0 push byte 24 jmp isr_common_stub ; 25: Reserved _isr25: cli push byte 0 push byte 25 jmp isr_common_stub ; 26: Reserved _isr26: cli push byte 0 push byte 26 jmp isr_common_stub ; 27: Reserved _isr27: cli push byte 0 push byte 27 jmp isr_common_stub ; 28: Reserved _isr28: cli push byte 0 push byte 28 jmp isr_common_stub ; 29: Reserved _isr29: cli push byte 0 push byte 29 jmp isr_common_stub ; 30: Reserved _isr30: cli push byte 0 push byte 30 jmp isr_common_stub ; 31: Reserved _isr31: cli push byte 0 push byte 31 jmp isr_common_stub ; We call a C function in here. We need to let the assembler know ; that '_fault_handler' exists in another file extern _fault_handler ; This is our common ISR stub. It saves the processor state, sets ; up for kernel mode segments, calls the C-level fault handler, ; and finally restores the stack frame. isr_common_stub: pusha push ds push es push fs push gs mov ax, 0x10 mov ds, ax mov es, ax mov fs, ax mov gs, ax mov eax, esp push eax mov eax, _fault_handler call eax pop eax pop gs pop fs pop es pop ds popa add esp, 8 iret Here's C Code: #include <isr/isr.h> const char* fault_messages[] = { "Division By Zero", "Debug", "Non Maskable Interrupt", "Breakpoint", "Into Detected Overflow", "Out of Bounds", "Invalid Opcode", "No Coprocessor", "Double Fault", "Coprocessor Segment Overrun", "Bad TSS", "Segment Not Present", "Stack Fault", "General Protection Fault", "Page Fault", "Unknown Interrupt", "Coprocessor Fault", "Alignment Check", "Machine Check", "Reserved", "Reserved", "Reserved", "Reserved", "Reserved", "Reserved", "Reserved", "Reserved", "Reserved", "Reserved", "Reserved", "Reserved", "Reserved" }; void _fault_handler(reg_dump_t* r) { if(r->int_no < 32) { puts(" Exception: "); puts(fault_messages[r->int_no]); for(;;); } } void isrs_install() { idt_set_gate(0,(unsigned)_isr0,0x08,0x8E); idt_set_gate(1,(unsigned)_isr1,0x08,0x8E); idt_set_gate(2,(unsigned)_isr2,0x08,0x8E); idt_set_gate(3,(unsigned)_isr3,0x08,0x8E); idt_set_gate(4,(unsigned)_isr4,0x08,0x8E); idt_set_gate(5,(unsigned)_isr5,0x08,0x8E); idt_set_gate(6,(unsigned)_isr6,0x08,0x8E); idt_set_gate(7,(unsigned)_isr7,0x08,0x8E); idt_set_gate(8,(unsigned)_isr8,0x08,0x8E); idt_set_gate(9,(unsigned)_isr9,0x08,0x8E); idt_set_gate(10,(unsigned)_isr10,0x08,0x8E); idt_set_gate(11,(unsigned)_isr11,0x08,0x8E); idt_set_gate(12,(unsigned)_isr12,0x08,0x8E); idt_set_gate(13,(unsigned)_isr13,0x08,0x8E); idt_set_gate(14,(unsigned)_isr14,0x08,0x8E); idt_set_gate(15,(unsigned)_isr15,0x08,0x8E); idt_set_gate(16,(unsigned)_isr16,0x08,0x8E); idt_set_gate(17,(unsigned)_isr17,0x08,0x8E); idt_set_gate(18,(unsigned)_isr18,0x08,0x8E); idt_set_gate(19,(unsigned)_isr19,0x08,0x8E); idt_set_gate(20,(unsigned)_isr20,0x08,0x8E); idt_set_gate(21,(unsigned)_isr21,0x08,0x8E); idt_set_gate(22,(unsigned)_isr22,0x08,0x8E); idt_set_gate(23,(unsigned)_isr23,0x08,0x8E); idt_set_gate(24,(unsigned)_isr24,0x08,0x8E); idt_set_gate(25,(unsigned)_isr25,0x08,0x8E); idt_set_gate(26,(unsigned)_isr26,0x08,0x8E); idt_set_gate(27,(unsigned)_isr27,0x08,0x8E); idt_set_gate(28,(unsigned)_isr28,0x08,0x8E); idt_set_gate(29,(unsigned)_isr29,0x08,0x8E); idt_set_gate(30,(unsigned)_isr30,0x08,0x8E); idt_set_gate(31,(unsigned)_isr31,0x08,0x8E); } And here's the idt_set_gate Code: void idt_set_gate(uint8_t index,uint64_t base,uint16_t sel,uint8_t flags)
{ // Base g(index).base_low = ((uintptr_t)base & 0xFFFF); g(index).base_hi = ((uintptr_t)base >> 16) & 0xFFFF; // Selector g(index).selector = sel; // Zero & Flags g(index).zero = 0; g(index).flags = flags | 0x60; } |
Author: | zvoncika [ Sun Dec 03, 2017 3:35 am ] |
Post subject: | Re: ISR Problem |
This also fires the exception: Code: asm volatile("mov $0, %edx\n"
"mov $0, %eax\n" "mov $0, %ecx\n" "div %ecx"); |
Author: | zvoncika [ Sun Dec 03, 2017 3:36 am ] |
Post subject: | Re: ISR Problem |
Nevermind, fixed it! I feel silly now...forgot to delete the "-O2" flag... |
Author: | Haoud [ Sun Dec 03, 2017 4:07 am ] |
Post subject: | Re: ISR Problem |
No problem (this has already happened to me) Good luck for the future |
Author: | Octocontrabass [ Sun Dec 03, 2017 12:20 pm ] |
Post subject: | Re: ISR Problem |
zvoncika wrote: After calling my isr_install() function, I divide by zero expecting the fault handler to be called. In C, division by zero is undefined behavior. That means when you try to divide by zero in a C program, the compiler may not actually generate code that tells the CPU to divide by zero. If you want to ensure your program causes #DE, you'll have to use assembly. (Changing the optimization level is not guaranteed to work either!) |
Author: | zvoncika [ Sun Dec 03, 2017 12:52 pm ] |
Post subject: | Re: ISR Problem |
Octocontrabass wrote: zvoncika wrote: After calling my isr_install() function, I divide by zero expecting the fault handler to be called. In C, division by zero is undefined behavior. That means when you try to divide by zero in a C program, the compiler may not actually generate code that tells the CPU to divide by zero. If you want to ensure your program causes #DE, you'll have to use assembly. (Changing the optimization level is not guaranteed to work either!) Thanks for letting be know! I solved it by disabling optimization. |
Author: | Octocontrabass [ Sun Dec 03, 2017 1:19 pm ] |
Post subject: | Re: ISR Problem |
zvoncika wrote: Octocontrabass wrote: (Changing the optimization level is not guaranteed to work either!) I solved it by disabling optimization.Disabling optimization is also not guaranteed to work. |
Author: | MichaelPetch [ Sun Dec 03, 2017 10:20 pm ] |
Post subject: | Re: ISR Problem |
You can avoid the optimizer doing away with the div by zero if you put 0 in a volatile variable and use the volatile as the denominator of the division. Something like: Code: volatile int zero = 0; Since the compiler can no longer assume the variable will be zero (might be modified asynchronously) it is forced to emit the division and it should produce an exception at run time. In your code you should be able to do this to generate the division:int divbyzero() { return 1/zero; } Code: volatile int tmp = divbyzero(); Edit: This is still undefined behaviour and a poor way of attempting to do it since the compiler won't guarantee that even at runtime that it won't check for a denominator of zero (on x86 this usually isn't the case but the compiler is allowed to emit such instructions if it so chooses). The only way to guarantee this exception is raised is with an external assembly function or inline assembly that does div by zero. Something simple like this should work:Code: __asm__ ("div %0" :: "r"(0)); . This should take whatever is in (e|r)ax (doesn't matter the value) and divide it by a register containing 0.
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Author: | zesterer [ Tue Dec 05, 2017 4:07 am ] |
Post subject: | Re: ISR Problem |
Don't turn optimisation off. If ANY level of optimisation breaks your code, it's because the code is broken and you should really fix it. If you want to perform a division by zero, it's as simple as: Code: volatile int i = 1 / 0; 'volatile' here ensures that the compiler won't optimise out the code. |
Author: | MichaelPetch [ Tue Dec 05, 2017 4:17 am ] |
Post subject: | Re: ISR Problem |
zesterer wrote: Code: volatile int i = 1 / 0; |
Author: | davidv1992 [ Tue Dec 05, 2017 6:36 am ] |
Post subject: | Re: ISR Problem |
zesterer wrote: Don't turn optimisation off. If ANY level of optimisation breaks your code, it's because the code is broken and you should really fix it. If you want to perform a division by zero, it's as simple as: Code: volatile int i = 1 / 0; 'volatile' here ensures that the compiler won't optimise out the code. I'm also afraid you misunderstand volatile here. The only thing it tells the compiler is that the variable i may be accessed/modified by other code it cant know about at (almost) any time. It doesn't actually do anything with the division. |
Author: | Octocontrabass [ Tue Dec 05, 2017 11:04 am ] |
Post subject: | Re: ISR Problem |
MichaelPetch wrote: You can avoid the optimizer doing away with the div by zero if you put 0 in a volatile variable and use the volatile as the denominator of the division. [...] Since the compiler can no longer assume the variable will be zero (might be modified asynchronously) it is forced to emit the division and it should produce an exception at run time. Division by zero in C is still undefined behavior, even if it can't be detected at compile time. There's no guarantee the compiler won't insert code specifically to check if the denominator is zero and crash in some other way. |
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