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Date:   Wed, 30 Oct 2019 16:03:02 +0100
From:   Torsten Duwe <duwe@suse.de>
To:     Mark Rutland <mark.rutland@arm.com>
Cc:     linux-arm-kernel@lists.infradead.org, Jessica Yu <jeyu@kernel.org>,
        Helge Deller <deller@gmx.de>,
        "James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
        linux-kernel@vger.kernel.org, amit.kachhap@arm.com,
        catalin.marinas@arm.com, james.morse@arm.com, jpoimboe@redhat.com,
        jthierry@redhat.com, linux-parisc@vger.kernel.org,
        mingo@redhat.com, peterz@infradead.org, rostedt@goodmis.org,
        svens@stackframe.org, takahiro.akashi@linaro.org, will@kernel.org
Subject: Re: [PATCHv2 2/8] module/ftrace: handle patchable-function-entry
Message-ID: <20191030150302.GA965@suse.de>
References: <20191029165832.33606-1-mark.rutland@arm.com>
 <20191029165832.33606-3-mark.rutland@arm.com>
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On Tue, Oct 29, 2019 at 04:58:26PM +0000, Mark Rutland wrote:
> When using patchable-function-entry, the compiler will record the
> callsites into a section named "__patchable_function_entries" rather
> than "__mcount_loc". Let's abstract this difference behind a new
> FTRACE_CALLSITE_SECTION, so that architectures don't have to handle this
> explicitly (e.g. with custom module linker scripts).
> 
> As parisc currently handles this explicitly, it is fixed up accordingly,
> with its custom linker script removed. Since FTRACE_CALLSITE_SECTION is
> only defined when DYNAMIC_FTRACE is selected, the parisc module loading
> code is updated to only use the definition in that case. When
> DYNAMIC_FTRACE is not selected, modules shouldn't have this section, so
> this removes some redundant work in that case.
> 
> I built parisc generic-{32,64}bit_defconfig with DYNAMIC_FTRACE enabled,
> and verified that the section made it into the .ko files for modules.

This is because of remaining #ifdeffery in include/asm-generic/vmlinux.lds.h:

#ifdef CC_USING_PATCHABLE_FUNCTION_ENTRY
#define MCOUNT_REC()    . = ALIGN(8);                           \
                        __start_mcount_loc = .;                 \
                        KEEP(*(__patchable_function_entries))   \
                        __stop_mcount_loc = .;
#else
#define MCOUNT_REC()    . = ALIGN(8);                           \
                        __start_mcount_loc = .;                 \
                        KEEP(*(__mcount_loc))                   \
                        __stop_mcount_loc = .;
#endif

Maybe you want to tackle that as well? I suggest to have at least one
FTRACE_CALLSITE_SECTION definition without double quotes. Alternatively, my
earlier solution just kept both sections, in case either one or both are
present.

                        KEEP(*(__patchable_function_entries))   \
                        KEEP(*(__mcount_loc))                   \

	Torsten