Messages in this thread | | | Date | Wed, 21 Nov 2012 11:50:20 -0800 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH v3 01/12] x86, boot: move verify_cpu.S after 0x200 |
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On 11/21/2012 11:45 AM, Yinghai Lu wrote: > On Wed, Nov 21, 2012 at 9:23 AM, H. Peter Anvin <hpa@zytor.com> wrote: >> On 11/20/2012 11:15 PM, Yinghai Lu wrote: >>> >>> We are short of space before 0x200 that is entry for startup_64. >>> >>> And we can not change startup_64 to other value --- ABI ? >> >> >> Here you are saying "I don't understand how this works." It is YOUR >> responsibility to find out and write a definite statement rather than >> leaving that to the reader, or expect the maintainer to edit this. > > actually, i can not find that out. > in the code of arch/x86/boot/compressed/head_64.S > > /* > * Be careful here startup_64 needs to be at a predictable > * address so I can export it in an ELF header. Bootloaders > * should look at the ELF header to find this address, as > * it may change in the future. > */ > .code64 > .org 0x200 > ENTRY(startup_64) > /* > * We come here either from startup_32 or directly from a > * 64bit bootloader. If we come here from a bootloader we depend on > * an identity mapped page table being provied that maps our > * entire text+data+bss and hopefully all of memory. > */ > #ifdef CONFIG_EFI_STUB > /* > * The entry point for the PE/COFF executable is 0x210, so only > * legacy boot loaders will execute this jmp. > */ > jmp preferred_addr > > .org 0x210 > mov %rcx, %rdi > > and it says that 0x200 will be changed later.. > > so you said it has to stay with 0x200, do you mean 0x210 from PE/COFF > force that? > > wonder if you are considering attatched patch to move startup_64 down... > we could kill one jmp. >
The comment is just plain wrong. It assumes you're loading an ELF file, whereas in practice that is rarely true.
This does explain why the poor ABI, though. A jump table at the beginning would have been a lot cleaner.
-hpa
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