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A free Windows-compatible Operating System - mirrored from GitHub
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The handlers for unexpected interrupts that we generate from asm macros use a push instruction with an 8 bit operand to push the interrupt number on the stack. Now the 8 bit push has the unfortunate behaviour of sign extending to 32 bit. But since the assembler is smart (or at least thinks so) it will not generate such a push instruction for values larger than 0x7f. This resulted in 7 bytes long stubs in the range of 0x30 .. 0x7f and 10 bytes long stubs after that. To fix this 128 is substracted from the value and later readded in the common code path. A second issue arose, because the assembler would start to use 8 bit relative short jumps as soon as the target was less than 127 bytes away, which happened for some of the higher interrupts, which then had a smaller stub then the others. Fix this by moving the stubs up in the code further away from the target label, so that always 32bit relative jumps will be used. These problems didn't show up so far, since we used the PIC and interrupts in the range of 0x30 .. 0x40 and the code that relied on the stubs all having the same length was working well. This changes with an APIC based hal, where interrupts of much higher number are likely to be used. svn path=/trunk/; revision=53679 |
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