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| author | Michael Ellerman <mpe@ellerman.id.au> | 2021-06-23 16:04:54 +0300 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2021-06-25 07:47:19 +0300 |
| commit | 24d33ac5b8ffb7a0e697344fea8591376162548f (patch) | |
| tree | 679b1b64eb78b45a7106fa84d80217ace9d23adb /arch/powerpc/platforms | |
| parent | c6c27e3d84648e6188fba314ae21a005e60bdcd4 (diff) | |
| download | linux-24d33ac5b8ffb7a0e697344fea8591376162548f.tar.xz | |
powerpc/64s: Make prom_init require RELOCATABLE
When we boot from open firmware (OF) using PPC_OF_BOOT_TRAMPOLINE, aka.
prom_init, we run parts of the kernel at an address other than the link
address. That happens because OF loads the kernel above zero (OF is at
zero) and we run prom_init before copying the kernel down to zero.
Currently that works even for non-relocatable kernels, because we do
various fixups to the prom_init code to make it run where it's loaded.
However those fixups are not sufficient if the kernel becomes large
enough. In that case prom_init()'s final call to __start() can end up
generating a plt branch:
bl c000000002000018 <00000078.plt_branch.__start>
That results in the kernel jumping to the linked address of __start,
0xc000000000000000, when really it needs to jump to the
0xc000000000000000 + the runtime address because the kernel is still
running at the load address.
We could do further shenanigans to handle that, see Jordan's patch for
example:
https://lore.kernel.org/linuxppc-dev/20210421021721.1539289-1-jniethe5@gmail.com
However it is much simpler to just require a kernel with prom_init() to
be built relocatable. The result works in all configurations without
further work, and requires less code.
This should have no effect on most people, as our defconfigs and
essentially all distro configs already have RELOCATABLE enabled.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210623130454.2542945-1-mpe@ellerman.id.au
Diffstat (limited to 'arch/powerpc/platforms')
| -rw-r--r-- | arch/powerpc/platforms/Kconfig | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/powerpc/platforms/Kconfig b/arch/powerpc/platforms/Kconfig index 2f071fb9694c..e02d29a9d12f 100644 --- a/arch/powerpc/platforms/Kconfig +++ b/arch/powerpc/platforms/Kconfig @@ -51,6 +51,7 @@ config PPC_NATIVE config PPC_OF_BOOT_TRAMPOLINE bool "Support booting from Open Firmware or yaboot" depends on PPC_BOOK3S_32 || PPC64 + select RELOCATABLE if PPC64 default y help Support from booting from Open Firmware or yaboot using an |