Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <ac4e3ceb-7de8-2c3f-4689-1730d811bf3d@linux.vnet.ibm.com>
Date:   Wed, 25 May 2022 15:44:04 +0530
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.5.0
Subject: Re: [RFC PATCH v2 0/7] objtool: Enable and implement --mcount option
 on powerpc
Content-Language: en-US
To:     Christophe Leroy <christophe.leroy@csgroup.eu>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        "aik@ozlabs.ru" <aik@ozlabs.ru>, mbenes@suse.cz,
        "peterz@infradead.org" <peterz@infradead.org>,
        "rostedt@goodmis.org" <rostedt@goodmis.org>, jpoimboe@redhat.com,
        "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
        Sathvika Vasireddy <sv@linux.ibm.com>
References: <cover.1653398233.git.christophe.leroy@csgroup.eu>
From:   Sathvika Vasireddy <sv@linux.vnet.ibm.com>
In-Reply-To: <cover.1653398233.git.christophe.leroy@csgroup.eu>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk

Hi Christophe,

On 24/05/22 18:47, Christophe Leroy wrote:
> This draft series adds PPC32 support to Sathvika's series.
> Verified on pmac32 on QEMU.
>
> It should in principle also work for PPC64 BE but for the time being
> something goes wrong. In the beginning I had a segfaut hence the first
> patch. But I still get no mcount section in the files.
Since PPC64 BE uses older elfv1 ABI, it prepends a dot to symbols.
And so, the relocation records in case of PPC64BE point to "._mcount",
rather than just "_mcount". We should be looking for "._mcount" to be
able to generate mcount_loc section in the files.

Like:

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 70be5a72e838..7da5bf8c7236 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2185,7 +2185,7 @@ static int classify_symbols(struct objtool_file *file)
                         if (arch_is_retpoline(func))
                                 func->retpoline_thunk = true;

-                       if ((!strcmp(func->name, "__fentry__")) || 
(!strcmp(func->name, "_mcount")))
+                       if ((!strcmp(func->name, "__fentry__")) || 
(!strcmp(func->name, "_mcount")) || (!strcmp(func->name, "._mcount")))
                                 func->fentry = true;

                         if (is_profiling_func(func->name))


With this change, I could see __mcount_loc section being
generated in individual ppc64be object files.

- Sathvika