36b01eb2d3
When compiled with gcc 4.6.1, 32-bit Sortix would triple fault during early boot: When the TLB is being flushed, somehow a garbage value had sneaked into Sortix::Memory::currentdir, and a non-page aligned (and garbage) page directory is loaded. (Triple fault, here we come!) However, adding a volatile addr_t foo after the currentdir variable actually caused the system to boot correctly - the garbage was written into that variable instead. To debug the problem, I set the foo value to 0: as long as !foo (hence the name nofoo) everything was alright. After closer examination I found that the initrd open code wrote to a pointer supplied by kernel.cpp. The element pointed to was on the stack. Worse, its address was the same as currentdir (now foo). Indeed, the stack had gone into the kernel's data segment! Turns out that this gcc configuration stores variables in the data segment in the reverse order they are defined in, whereas previous compilers did the opposite. The hack used to set up the stack during early boot relied on this (now obviously incorrect) fact. In effect, the stack was initialized to the end of the stack, not the start of it: completely ignoring all the nice stack space allocated in kernel.cpp. I did not see that one coming.
70 lines
1.7 KiB
ArmAsm
70 lines
1.7 KiB
ArmAsm
/******************************************************************************
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COPYRIGHT(C) JONAS 'SORTIE' TERMANSEN 2011.
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This file is part of Sortix.
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Sortix is free software: you can redistribute it and/or modify it under the
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terms of the GNU General Public License as published by the Free Software
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Foundation, either version 3 of the License, or (at your option) any later
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version.
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Sortix is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
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details.
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You should have received a copy of the GNU General Public License along
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with Sortix. If not, see <http://www.gnu.org/licenses/>.
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boot.s
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Bootstraps the kernel and passes over control from the boot-loader to the
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kernel main function.
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******************************************************************************/
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.globl beginkernel, _beginkernel
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.globl start, _start
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.section .text
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.type _beginkernel, @function
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beginkernel:
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_beginkernel:
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movw $0x736, 0xB83E8
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movw $0x734, 0xB83EA
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movw $0x753, 0xB83EE
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movw $0x74F, 0xB83F0
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movw $0x752, 0xB83F2
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movw $0x754, 0xB83F4
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movw $0x749, 0xB83F6
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movw $0x758, 0xB83F8
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# Initialize the stack pointer.
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movq $stack, %rsp
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addq $65536, %rsp # 64 KiB, see kernel.cpp
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# Reset EFLAGS.
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# pushl $0
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# popf
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# Push the pointer to the Multiboot information structure.
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mov %rbx, %rsi
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# Push the magic value.
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mov %rax, %rdi
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call KernelInit
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.globl HaltKernel
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HaltKernel:
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cli
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hlt
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jmp HaltKernel
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.globl WaitForInterrupt
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.type WaitForInterrupt, @function # void WaitForInterrupt();
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WaitForInterrupt:
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hlt
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ret
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