Fix UEFI support for ARM
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Authored by gonzo on Jan 9 2017, 7:52 PM.

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Summary

ARM UEFI support is borken on clang 3.9.0 because for two reasons:

without -fPIC clang generates abosulte jump tables for switch statement
ldscript merges .rel.data.rel.ro into .data section, so some relocations are lost in final binary (boot1.sym.full)

Test Plan

boot QEMU VIRT kernel using EFI

Repository

rS FreeBSD src repository - subversion

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Build Status

Buildable 6669
Build 6887: arc lint + arc unit

gonzo retitled this revision from to Fix UEFI support for ARM.

gonzo updated this object.

gonzo edited the test plan for this revision. (Show Details)

gonzo added a reviewer: andrew.

sys/boot/efi/boot1/Makefile
73	Do we need this in the loader.efi Makefile? If so it should be moved to `sys/boot/efi/Makefile.inc`
sys/boot/efi/loader/bootinfo.c
354–368	Is this intentional?

sys/boot/efi/boot1/Makefile
73	I assume that it's required. But I will check
sys/boot/efi/loader/bootinfo.c
354–368	Yes. Without this change relocation happens twice. I think previously it wasn't relocated because .rel.data.rel.ro was merged into .data and that relocations were lost. With fixed ldscript these values relocated EFI loader.

sys/boot/efi/loader/bootinfo.c
354–368	On arm when building for EFI `__elfN(relocation_offset)` is set to `0` so this code should have been a nop. If it is now non-zero that would indicate a bug somewhere that this is picking up.

Remove unnecessary -fPIC and also fix one-off error in .bss zeroing code

Move -fPIC to proper location

-fPIC is required by loader.efi so I moved the flag to proper location
the relocation_offset bug was due to off-by-one error in .bss zeroing routine. It wrote zero to __bss_end which AFAIU should be excluded from range. That address was actually entry for elf32_relocation_offset in offset table.