Am Dienstag, 16 August 2016, 16:52:54 schrieb Balbir Singh:

On 16/08/16 09:25, Thiago Jung Bauermann wrote:

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Am Montag, 15 August 2016, 17:46:34 schrieb Balbir Singh:

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On Thu, Aug 11, 2016 at 08:08:09PM -0300, Thiago Jung Bauermann wrote:

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+/**
+ * elf64_apply_relocate_add - apply 64 bit RELA relocations
+ * @elf_info:		Support information for the ELF binary being

relocated.

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+ * @strtab:		String table for the associated symbol

table.

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+ * @symindex:		Section header index for the associated

symbol table.

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+ * @relsec:		Section header index for the relocations to

apply.

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+ * @obj_name:		The name of the ELF binary, for information

messages.

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+ */
+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.

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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.

zImage on ppc64 BE is an ELF32 file. This patch set only supports loading 
ELF files of the same class as the kernel, so a 64 bit kernel can't load an 
ELF32 file. It would be possible to add such support, but it would be a new 
feature.

The distros I was able to check on ppc64 LE and BE all use vmlinux.
kexec-tools with kexec_load also doesn't support zImage. Do you think it is 
important to support zImage?

-- 
[]'s
Thiago Jung Bauermann
IBM Linux Technology Center