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

diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
index 05ce15b854e2775e28e48a5648ce452c0445d343..a5bf355ce1d632f032b855ff4089365d1d5b3ee1 100644 (file)
--- a/arch/powerpc/kernel/prom_init.c
+++ b/arch/powerpc/kernel/prom_init.c
@@ -3243,54 +3243,6 @@ static void __init prom_check_initrd(unsigned long r3, unsigned long r4)
 #endif /* CONFIG_BLK_DEV_INITRD */
 }
 
-#ifdef CONFIG_PPC64
-#ifdef CONFIG_RELOCATABLE
-static void reloc_toc(void)
-{
-}
-
-static void unreloc_toc(void)
-{
-}
-#else
-static void __reloc_toc(unsigned long offset, unsigned long nr_entries)
-{
-       unsigned long i;
-       unsigned long *toc_entry;
-
-       /* Get the start of the TOC by using r2 directly. */
-       asm volatile("addi %0,2,-0x8000" : "=b" (toc_entry));
-
-       for (i = 0; i < nr_entries; i++) {
-               *toc_entry = *toc_entry + offset;
-               toc_entry++;
-       }
-}
-
-static void reloc_toc(void)
-{
-       unsigned long offset = reloc_offset();
-       unsigned long nr_entries =
-               (__prom_init_toc_end - __prom_init_toc_start) / sizeof(long);
-
-       __reloc_toc(offset, nr_entries);
-
-       mb();
-}
-
-static void unreloc_toc(void)
-{
-       unsigned long offset = reloc_offset();
-       unsigned long nr_entries =
-               (__prom_init_toc_end - __prom_init_toc_start) / sizeof(long);
-
-       mb();
-
-       __reloc_toc(-offset, nr_entries);
-}
-#endif
-#endif
-
 #ifdef CONFIG_PPC_SVM
 /*
  * Perform the Enter Secure Mode ultracall.
@@ -3324,14 +3276,12 @@ static void __init setup_secure_guest(unsigned long kbase, unsigned long fdt)
         * relocated it so the check will fail. Restore the original image by
         * relocating it back to the kernel virtual base address.
         */
-       if (IS_ENABLED(CONFIG_RELOCATABLE))
-               relocate(KERNELBASE);
+       relocate(KERNELBASE);
 
        ret = enter_secure_mode(kbase, fdt);
 
        /* Relocate the kernel again. */
-       if (IS_ENABLED(CONFIG_RELOCATABLE))
-               relocate(kbase);
+       relocate(kbase);
 
        if (ret != U_SUCCESS) {
                prom_printf("Returned %d from switching to secure mode.\n", ret);
@@ -3359,8 +3309,6 @@ unsigned long __init prom_init(unsigned long r3, unsigned long r4,
 #ifdef CONFIG_PPC32
        unsigned long offset = reloc_offset();
        reloc_got2(offset);
-#else
-       reloc_toc();
 #endif
 
        /*
@@ -3537,8 +3485,6 @@ unsigned long __init prom_init(unsigned long r3, unsigned long r4,
 
 #ifdef CONFIG_PPC32
        reloc_got2(-offset);
-#else
-       unreloc_toc();
 #endif
 
        /* Move to secure memory if we're supposed to be secure guests. */

diff --git a/arch/powerpc/platforms/Kconfig b/arch/powerpc/platforms/Kconfig
index 2f071fb9694ccd874acc9f0a95169bf10745b1aa..e02d29a9d12ff63a134c924a71f54a4ee967fa76 100644 (file)
--- 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