linux-kernel - Re: [PATCH] arm64: ftrace: fix building without CONFIG

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Date:   Mon, 12 Jun 2017 15:01:36 +0200
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Will Deacon <will.deacon@....com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>, Jessica Yu <jeyu@...nel.org>,
        Rusty Russell <rusty@...tcorp.com.au>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: ftrace: fix building without CONFIG_MODULES

On 12 June 2017 at 14:48, Will Deacon <will.deacon@....com> wrote:
> On Fri, Jun 09, 2017 at 08:57:31PM +0200, Arnd Bergmann wrote:
>> On Fri, Jun 9, 2017 at 1:38 PM, Will Deacon <will.deacon@....com> wrote:
>> > On Fri, Jun 09, 2017 at 12:27:06PM +0200, Arnd Bergmann wrote:
>> >> When CONFIG_MODULES is disabled, we cannot dereference a module pointer:
>> >>
>> >> arch/arm64/kernel/ftrace.c: In function 'ftrace_make_call':
>> >> arch/arm64/kernel/ftrace.c:107:36: error: dereferencing pointer to incomplete type 'struct module'
>> >>    trampoline = (unsigned long *)mod->arch.ftrace_trampoline;
>> >>
>> >> Also, the within_module() function is not defined:
>> >>
>> >> arch/arm64/kernel/ftrace.c: In function 'ftrace_make_nop':
>> >> arch/arm64/kernel/ftrace.c:171:8: error: implicit declaration of function 'within_module'; did you mean 'init_module'? [-Werror=implicit-function-declaration]
>> >>
>> >> This addresses both by adding the appropriate stubs.
>> >>
>> >> Fixes: e71a4e1bebaf ("arm64: ftrace: add support for far branches to dynamic ftrace")
>> >> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>> >> ---
>> >>  arch/arm64/include/asm/module.h | 6 ++++++
>> >>  arch/arm64/kernel/ftrace.c      | 2 +-
>> >>  include/linux/module.h          | 5 +++++
>> >>  3 files changed, 12 insertions(+), 1 deletion(-)
>> >
>> > I can't seem to reproduce this simply by disabling MODULES in defconfig.
>> > Could you share your .config, please?
>>
>> This is the randconfig I used: https://pastebin.com/SfKBY7f8
>
> Thanks, I was forgetting to enable ftrace. I think a simpler patch (and one
> that I can just apply via arm64) is switching the IS_ENABLEDs out for
> #ifdefs.

I agree that this makes more sense in this particular case.

Acked-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>

Interestingly, ARM64_MODULE_PLTS does not depend on CONFIG_MODULES,
but I can't remember whether that was deliberate or an oversight.

> See below.
>
> --->8
>
> diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
> index 8a42be0693c9..401aa27808a4 100644
> --- a/arch/arm64/kernel/ftrace.c
> +++ b/arch/arm64/kernel/ftrace.c
> @@ -71,11 +71,12 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
>  int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
>  {
>         unsigned long pc = rec->ip;
> -       long offset = (long)pc - (long)addr;
>         u32 old, new;
>
> -       if (IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) &&
> -           (offset < -SZ_128M || offset >= SZ_128M)) {
> +#ifdef CONFIG_ARM64_MODULE_PLTS
> +       long offset = (long)pc - (long)addr;
> +
> +       if (offset < -SZ_128M || offset >= SZ_128M) {
>                 unsigned long *trampoline;
>                 struct module *mod;
>
> @@ -121,6 +122,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
>                 }
>                 addr = (unsigned long)&trampoline[1];
>         }
> +#endif /* CONFIG_ARM64_MODULE_PLTS */
>
>         old = aarch64_insn_gen_nop();
>         new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
> @@ -135,12 +137,13 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
>                     unsigned long addr)
>  {
>         unsigned long pc = rec->ip;
> -       long offset = (long)pc - (long)addr;
>         bool validate = true;
>         u32 old = 0, new;
>
> -       if (IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) &&
> -           (offset < -SZ_128M || offset >= SZ_128M)) {
> +#ifdef CONFIG_ARM64_MODULE_PLTS
> +       long offset = (long)pc - (long)addr;
> +
> +       if (offset < -SZ_128M || offset >= SZ_128M) {
>                 u32 replaced;
>
>                 /*
> @@ -177,6 +180,7 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
>                 old = aarch64_insn_gen_branch_imm(pc, addr,
>                                                   AARCH64_INSN_BRANCH_LINK);
>         }
> +#endif /* CONFIG_ARM64_MODULE_PLTS */
>
>         new = aarch64_insn_gen_nop();
>