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Date: Fri, 28 May 2021 12:34:35 +0200
From: Greg Kurz <groug@kaod.org>
To: Roman Bolshakov <r.bolshakov@yadro.com>
Subject: Re: [PATCH] Revert "powerpc: Switch to relative jump labels"
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Cc: Anastasia Kovaleva <a.kovaleva@yadro.com>, linux@yadro.com,
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On Fri, 28 May 2021 04:29:43 +0300
Roman Bolshakov <r.bolshakov@yadro.com> wrote:

> This reverts commit b0b3b2c78ec075cec4721986a95abbbac8c3da4f.
>=20
> Otherwise, direct kernel boot with initramfs no longer works in QEMU.
> It's broken in some bizarre way because a valid initramfs is not
> recognized anymore:
>=20
>   Found initrd at 0xc000000001f70000:0xc000000003d61d64
>   rootfs image is not initramfs (XZ-compressed data is corrupt); looks li=
ke an initrd
>=20
> The issue is observed on v5.13-rc3 if the kernel is built with
> defconfig, GCC 7.5.0 and GNU ld 2.32.0.
>=20
> Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
> Reported-by: Anastasia Kovaleva <a.kovaleva@yadro.com>
> Signed-off-by: Roman Bolshakov <r.bolshakov@yadro.com>
> ---

I'm observing the very same issue and reverting the offending commit
fixes it indeed. Until someone has investigated the root cause, this
looks like a reasonable bug fix to me.

Reviewed-by: Greg Kurz <groug@kaod.org>

and

Tested-by: Greg Kurz <groug@kaod.org>

>  arch/powerpc/Kconfig                  |  1 -
>  arch/powerpc/include/asm/jump_label.h | 21 +++++++++++++++------
>  arch/powerpc/kernel/jump_label.c      |  4 ++--
>  3 files changed, 17 insertions(+), 9 deletions(-)
>=20
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 088dd2afcfe4..59e0d55ee01d 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -189,7 +189,6 @@ config PPC
>  =09select HAVE_ARCH_HUGE_VMALLOC=09=09if HAVE_ARCH_HUGE_VMAP
>  =09select HAVE_ARCH_HUGE_VMAP=09=09if PPC_BOOK3S_64 && PPC_RADIX_MMU
>  =09select HAVE_ARCH_JUMP_LABEL
> -=09select HAVE_ARCH_JUMP_LABEL_RELATIVE
>  =09select HAVE_ARCH_KASAN=09=09=09if PPC32 && PPC_PAGE_SHIFT <=3D 14
>  =09select HAVE_ARCH_KASAN_VMALLOC=09=09if PPC32 && PPC_PAGE_SHIFT <=3D 1=
4
>  =09select HAVE_ARCH_KFENCE=09=09=09if PPC32
> diff --git a/arch/powerpc/include/asm/jump_label.h b/arch/powerpc/include=
/asm/jump_label.h
> index 2d5c6bec2b4f..09297ec9fa52 100644
> --- a/arch/powerpc/include/asm/jump_label.h
> +++ b/arch/powerpc/include/asm/jump_label.h
> @@ -20,8 +20,7 @@ static __always_inline bool arch_static_branch(struct s=
tatic_key *key, bool bran
>  =09asm_volatile_goto("1:\n\t"
>  =09=09 "nop # arch_static_branch\n\t"
>  =09=09 ".pushsection __jump_table,  \"aw\"\n\t"
> -=09=09 ".long 1b - ., %l[l_yes] - .\n\t"
> -=09=09 JUMP_ENTRY_TYPE "%c0 - .\n\t"
> +=09=09 JUMP_ENTRY_TYPE "1b, %l[l_yes], %c0\n\t"
>  =09=09 ".popsection \n\t"
>  =09=09 : :  "i" (&((char *)key)[branch]) : : l_yes);
> =20
> @@ -35,8 +34,7 @@ static __always_inline bool arch_static_branch_jump(str=
uct static_key *key, bool
>  =09asm_volatile_goto("1:\n\t"
>  =09=09 "b %l[l_yes] # arch_static_branch_jump\n\t"
>  =09=09 ".pushsection __jump_table,  \"aw\"\n\t"
> -=09=09 ".long 1b - ., %l[l_yes] - .\n\t"
> -=09=09 JUMP_ENTRY_TYPE "%c0 - .\n\t"
> +=09=09 JUMP_ENTRY_TYPE "1b, %l[l_yes], %c0\n\t"
>  =09=09 ".popsection \n\t"
>  =09=09 : :  "i" (&((char *)key)[branch]) : : l_yes);
> =20
> @@ -45,12 +43,23 @@ static __always_inline bool arch_static_branch_jump(s=
truct static_key *key, bool
>  =09return true;
>  }
> =20
> +#ifdef CONFIG_PPC64
> +typedef u64 jump_label_t;
> +#else
> +typedef u32 jump_label_t;
> +#endif
> +
> +struct jump_entry {
> +=09jump_label_t code;
> +=09jump_label_t target;
> +=09jump_label_t key;
> +};
> +
>  #else
>  #define ARCH_STATIC_BRANCH(LABEL, KEY)=09=09\
>  1098:=09nop;=09=09=09=09=09\
>  =09.pushsection __jump_table, "aw";=09\
> -=09.long 1098b - ., LABEL - .;=09=09\
> -=09FTR_ENTRY_LONG KEY;=09=09=09\
> +=09FTR_ENTRY_LONG 1098b, LABEL, KEY;=09\
>  =09.popsection
>  #endif
> =20
> diff --git a/arch/powerpc/kernel/jump_label.c b/arch/powerpc/kernel/jump_=
label.c
> index ce87dc5ea23c..144858027fa3 100644
> --- a/arch/powerpc/kernel/jump_label.c
> +++ b/arch/powerpc/kernel/jump_label.c
> @@ -11,10 +11,10 @@
>  void arch_jump_label_transform(struct jump_entry *entry,
>  =09=09=09       enum jump_label_type type)
>  {
> -=09struct ppc_inst *addr =3D (struct ppc_inst *)jump_entry_code(entry);
> +=09struct ppc_inst *addr =3D (struct ppc_inst *)(unsigned long)entry->co=
de;
> =20
>  =09if (type =3D=3D JUMP_LABEL_JMP)
> -=09=09patch_branch(addr, jump_entry_target(entry), 0);
> +=09=09patch_branch(addr, entry->target, 0);
>  =09else
>  =09=09patch_instruction(addr, ppc_inst(PPC_INST_NOP));
>  }