On 16/08/16 09:25, Thiago Jung Bauermann wrote:
> Am Montag, 15 August 2016, 17:46:34 schrieb Balbir Singh:
>> On Thu, Aug 11, 2016 at 08:08:09PM -0300, Thiago Jung Bauermann wrote:
>>> +/**
>>> + * elf64_apply_relocate_add - apply 64 bit RELA relocations
>>> + * @elf_info: Support information for the ELF binary being
> relocated.
>>> + * @strtab: String table for the associated symbol
> table.
>>> + * @symindex: Section header index for the associated
> symbol table.
>>> + * @relsec: Section header index for the relocations to
> apply.
>>> + * @obj_name: The name of the ELF binary, for information
> messages.
>>> + */
>>> +int elf64_apply_relocate_add(const struct elf_info *elf_info,
>>> + const char *strtab, unsigned int symindex,
>>> + unsigned int relsec, const char *obj_name)
>>> +{
>>> + unsigned int i;
>>> + Elf64_Shdr *sechdrs = elf_info->sechdrs;
>>> + Elf64_Rela *rela = (void *)sechdrs[relsec].sh_addr;
>>> + Elf64_Sym *sym;
>>> + unsigned long *location;
>>> + unsigned long value;
>>> +
>>
>> For the relocatable kernel we expect only
>>
>> R_PPC64_RELATIVE
>> R_PPC64_NONE
>> R_PPC64_ADDR64
>>
>> In the future we can use this to check/assert the usage of this
>> for the core kernel (vmlinux) when loaded.
>>
>> Did we check elf64_apply_relocate_add with zImage and vmlinux?
>
> kexec_file_load doesn't call call elf64_apply_relocate_add on the kernel
> image, it only uses it to relocate the purgatory. So whether it is loading a
> zImage or a vmlinux file, the function will work in the same way since the
> purgatory binary is the same regardless of the kernel image format.
Thanks for clarifying.
>
> For the same reason, as it currently stands kexec_file_load can't check the
> relocation types used in the kernel image. But it is possible to add such a
> check/assertion in kexec_elf_64.c:build_elf_exec_info if we want.
>
> I tested kexec_file_load on both relocatable and non-relocatable vmlinux and
> it works correctly.
>
> I hadn't tested with zImage yet. I just did, and I had two problems:
>
> 1. For some reason, it has an INTERP segment. This patch series doesn't
> support loading program interpreters for ELF binaries, so
> kexec_elf_64.c:build_elf_exec_info refuses to load them.
>
> 2. If I disable the check for the INTERP segment, the zImage file loads
> correctly, but then I get an exception during reboot when loading the kexec
> image, right before jumping into the purgatory. I suspect this is because
> the LOAD segment has a virtual address of 0, and the first kernel is not
> coping well with that. But I still have to debug it further.
>
> Is there a reason for the zImage ELF header to request an interpreter and to
> have a virtual address of 0?
>
Not that I am aware of.
Balbir Singh
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