Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] perf symbol: ignore $a/$d symbols for ARM modules
To:     Lexi Shao <shaolexi@huawei.com>, linux-perf-users@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     acme@kernel.org, mark.rutland@arm.com, peterz@infradead.org,
        mingo@redhat.com, alexander.shishkin@linux.intel.com,
        jolsa@redhat.com, namhyung@kernel.org, qiuxi1@huawei.com,
        nixiaoming@huawei.com, wangbing6@huawei.com
References: <20211027095235.123358-1-shaolexi@huawei.com>
From:   James Clark <james.clark@arm.com>
Message-ID: <0631949b-6cde-dee6-6a77-5b826938ce79@arm.com>
Date:   Thu, 28 Oct 2021 09:44:26 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.13.0
MIME-Version: 1.0
In-Reply-To: <20211027095235.123358-1-shaolexi@huawei.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk


On 27/10/2021 10:52, Lexi Shao wrote:
> On ARM machine, kernel symbols from modules can be resolved to $a
> instead of printing the actual symbol name. Ignore symbols starting with
> "$" when building kallsyms rbtree.
> 
> A sample stacktrace is shown as follows:
> 
> c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms])
> bf4a66d8 $a+0x78 ([test_module])
> c0a4f5f4 kthread+0x15c ([kernel.kallsyms])
> c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms])
> 
> On ARM machine, $a/$d symbols are used by the compiler to mark the
> beginning of code/data part in code section. These symbols are filtered
> out when linking vmlinux(see scripts/kallsyms.c ignored_prefixes), but
> are left on modules. So there are $a symbols in /proc/kallsyms which
> share the same addresses with the actual module symbols and confuses perf
> when resolving symbols.
> 
> After this patch, the module symbol name is printed:
> 
> c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms])
> bf4a66d8 test_func+0x78 ([test_module])
> c0a4f5f4 kthread+0x15c ([kernel.kallsyms])
> c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms])
> 
> Signed-off-by: Lexi Shao <shaolexi@huawei.com>

Reviewed-by: James Clark <james.clark@arm.com>

> ---
>  tools/perf/util/symbol.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index 0fc9a5410739..35116aed74eb 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -702,6 +702,10 @@ static int map__process_kallsym_symbol(void *arg, const char *name,
>  	if (!symbol_type__filter(type))
>  		return 0;
>  
> +	/* Ignore local symbols for ARM modules */
> +	if (name[0] == '$')
> +		return 0;
> +
>  	/*
>  	 * module symbols are not sorted so we add all
>  	 * symbols, setting length to 0, and rely on
>