linux-kernel - Re: [PATCH] asm-generic/io: Add _RET_IP_ to MMIO trace for more accurate debug info

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Message-ID: <20221024120929.41241e07@gandalf.local.home>
Date:   Mon, 24 Oct 2022 12:09:29 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sai Prakash Ranjan <quic_saipraka@...cinc.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-arch@...r.kernel.org>, <quic_satyap@...cinc.com>
Subject: Re: [PATCH] asm-generic/io: Add _RET_IP_ to MMIO trace for more
 accurate debug info

On Mon, 17 Oct 2022 20:04:50 +0530
Sai Prakash Ranjan <quic_saipraka@...cinc.com> wrote:

> Due to compiler optimizations like inlining, there are cases where
> MMIO traces using _THIS_IP_ for caller information might not be
> sufficient to provide accurate debug traces.
> 
> 1) With optimizations (Seen with GCC):
> 
> In this case, _THIS_IP_ works fine and prints the caller information
> since it will be inlined into the caller and we get the debug traces
> on who made the MMIO access, for ex:
> 
> rwmmio_read: qcom_smmu_tlb_sync+0xe0/0x1b0 width=32 addr=0xffff8000087447f4
> rwmmio_post_read: qcom_smmu_tlb_sync+0xe0/0x1b0 width=32 val=0x0 addr=0xffff8000087447f4
> 
> 2) Without optimizations (Seen with Clang):
> 
> _THIS_IP_ will not be sufficient in this case as it will print only
> the MMIO accessors itself which is of not much use since it is not
> inlined as below for example:
> 
> rwmmio_read: readl+0x4/0x80 width=32 addr=0xffff8000087447f4
> rwmmio_post_read: readl+0x48/0x80 width=32 val=0x4 addr=0xffff8000087447f4
> 
> So in order to handle this second case as well irrespective of the compiler
> optimizations, add _RET_IP_ to MMIO trace to make it provide more accurate
> debug information in all these scenarios.
> 
> Before:
> 
> rwmmio_read: readl+0x4/0x80 width=32 addr=0xffff8000087447f4
> rwmmio_post_read: readl+0x48/0x80 width=32 val=0x4 addr=0xffff8000087447f4
> 
> After:
> 
> rwmmio_read: qcom_smmu_tlb_sync+0xe0/0x1b0 -> readl+0x4/0x80 width=32 addr=0xffff8000087447f4
> rwmmio_post_read: qcom_smmu_tlb_sync+0xe0/0x1b0 -> readl+0x4/0x80 width=32 val=0x0 addr=0xffff8000087447f4
> 
> Fixes: 210031971cdd ("asm-generic/io: Add logging support for MMIO accessors")
> Signed-off-by: Sai Prakash Ranjan <quic_saipraka@...cinc.com>


Acked-by: Steven Rostedt (Google) <rostedt@...dmis.org>

What tree should this go through?

-- Steve