linux-kernel - Re: ftrace: Proposal for an Alternative RecordMcount framework

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Message-ID: <20180227161252.25162d81@vmware.local.home>
Date:   Tue, 27 Feb 2018 16:12:52 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Alan Kao <alankao@...estech.com>
Cc:     Palmer Dabbelt <palmer@...ive.com>, Albert Ou <albert@...ive.com>,
        <sw-dev@...ups.riscv.org>, <linux-kernel@...r.kernel.org>,
        <greentime@...estech.com>, <zong@...estech.com>
Subject: Re: ftrace: Proposal for an Alternative RecordMcount framework

On Tue, 27 Feb 2018 18:04:26 +0800
Alan Kao <alankao@...estech.com> wrote:
 
> 1. During the final linking stages, do "objdump vmlinux.o | grep ..." [2]

Note, doing it at that stage takes the longest time. It makes small
changes much longer to compile. That said...

> 2. Form the output as an ELF objecj
> 3. Link the object to __mcount_loc_start symbol
> 4. Done
> 
> With the similar reason as the patch [3], we should mark _mcount to be
> a weak symbol to prevent it from being relaxed later.
> 
> We would like to know your opinion and comments on this.
> Thanks!

What about just having your arch use recordmcount.c instead? It doesn't
do any grepping. It is an elf reader and modifier and modifies the .o
file directly.

Note, I will be rewriting that code in the near future too, to
consolidate it with objtool.

-- Steve