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Date:   Mon, 10 Oct 2022 17:19:02 +0530
From:   "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Subject: Re: [PATCH v4 00/16] objtool: Enable and implement --mcount option on
 powerpc
To:     linuxppc-dev@lists.ozlabs.org,
        Sathvika Vasireddy <sv@linux.ibm.com>, jpoimboe@redhat.com
Cc:     aik@ozlabs.ru, chenzhongjin@huawei.com,
        christophe.leroy@csgroup.eu, linux-kernel@vger.kernel.org,
        mbenes@suse.cz, mingo@redhat.com, mpe@ellerman.id.au,
        npiggin@gmail.com, peterz@infradead.org, rostedt@goodmis.org
References: <20221002104240.1316480-1-sv@linux.ibm.com>
In-Reply-To: <20221002104240.1316480-1-sv@linux.ibm.com>
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Sathvika Vasireddy wrote:
> This patchset enables and implements objtool --mcount
> option on powerpc. This applies atop powerpc/merge branch.
>=20
> Changelog:
>=20
> ----
> v4:
>=20
> * Patch 11/16 - Introduce a new config option
> 		CONFIG_HAVE_OBJTOOL_NOP_MCOUNT as a means for
> 		architectures to enable nop'ing ftrace locations.
>=20
> 	      - Remove Acked-by tag from Peter Zijlstra (Intel),
> 		and Reviewed-by tag from Christophe Leroy.=20
> 		[This is done because I reworked the patch to add
> 		a new config option to objtool. Please let me know
> 		if you want me to retain the tags. Thanks!]
>=20
> * Patch 16/16 - Rework the patch to handle only 'bl' instruction
> 		decoding.=20

With changes to the two patches in this series that I have described,=20
and with my patch to have ftrace ignore weak symbols (*) applied, I=20
built a ppc64le config.

(*) http://lkml.kernel.org/r/20220809105425.424045-1-naveen.n.rao@linux.vne=
t.ibm.com

I then used the below diff to disable objtool and to build with=20
recordmcount:

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 7e28a8fd4c24fa..81c9f895d69012 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -238,8 +238,6 @@ config PPC
        select HAVE_MOD_ARCH_SPECIFIC
        select HAVE_NMI                         if PERF_EVENTS || (PPC64 &&=
 PPC_BOOK3S)
        select HAVE_OPTPROBES
-       select HAVE_OBJTOOL                     if PPC32 || MPROFILE_KERNEL
-       select HAVE_OBJTOOL_MCOUNT              if HAVE_OBJTOOL
        select HAVE_PERF_EVENTS
        select HAVE_PERF_EVENTS_NMI             if PPC64
        select HAVE_PERF_REGS

Comparing available_filter_functions across the two builds showed the=20
below differences:
  $ diff ftrace_funcs_recordmcount_20221010.sort.out ftrace_funcs_objtool_2=
0221010.sort.out=20
  6799d6798
  < __dev_alloc_name
  6800a6800
  > dev_alloc_name_ns
  11680d11679
  < find_zone.isra.0
  22396a22396
  > ns_capable_common.part.0

All the above changes are down to compiler optimizations and shuffling=20
due to CONFIG_OBJTOOL being enabled and changing annotate_unreachable().

As such, for this series:
Reviewed-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Tested-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>


Josh,
Are you ok if this series is taken in through the powerpc tree?


- Naveen