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@@ -76,26 +76,28 @@ The starting address is formed by adding the base address to the value in the EI
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We get `0xfffffff0`, which is 16 bytes below 4GB. This point is called the [Reset vector](https://en.wikipedia.org/wiki/Reset_vector). This is the memory location at which the CPU expects to find the first instruction to execute after reset. It contains a [jump](https://en.wikipedia.org/wiki/JMP_%28x86_instruction%29) (`jmp`) instruction that usually points to the BIOS entry point. For example, if we look in the [coreboot](https://www.coreboot.org/) source code (`src/cpu/x86/16bit/reset16.inc`), we will see:
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```assembly
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- .section ".reset"
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+ .section ".reset", "ax", %progbits
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.code16
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-.globl reset_vector
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-reset_vector:
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+.globl _start
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+_start:
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.byte 0xe9
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- .int _start - ( . + 2 )
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+ .int _start16bit - ( . + 2 )
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...
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```
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-Here we can see the `jmp` instruction [opcode](http://ref.x86asm.net/coder32.html#xE9), which is `0xe9`, and its destination address at `_start - ( . + 2)`.
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+Here we can see the `jmp` instruction [opcode](http://ref.x86asm.net/coder32.html#xE9), which is `0xe9`, and its destination address at `_start16bit - ( . + 2)`.
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-We can also see that the `reset` section is `16` bytes and that is compiled to start from `0xfffffff0` address (`src/cpu/x86/16bit/reset16.lds`):
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+We can also see that the `reset` section is `16` bytes and that is compiled to start from `0xfffffff0` address (`src/cpu/x86/16bit/reset16.ld`):
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```
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SECTIONS {
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+ /* Trigger an error if I have an unuseable start address */
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+ _bogus = ASSERT(_start16bit >= 0xffff0000, "_start16bit too low. Please report.");
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_ROMTOP = 0xfffffff0;
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. = _ROMTOP;
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.reset . : {
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- *(.reset)
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- . = 15 ;
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+ *(.reset);
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+ . = 15;
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BYTE(0x00);
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}
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}
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