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

[Sai Prakash Ranjan]

Hi Arnd,

On 10/26/2022 7:17 PM, Sai Prakash Ranjan wrote:
> Hi Steve,
>
> On 10/24/2022 9:39 PM, Steven Rostedt wrote:
> > On Mon, 17 Oct 2022 20:04:50 +0530
> > Sai Prakash Ranjan <quic_saipraka@xxxxxxxxxxx> 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@xxxxxxxxxxx>
> >
> >
> > Acked-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
> >
> > What tree should this go through?
> >
> > -- Steve
>
>
> Thanks for the ack, with this I believe Arnd can take it through his 
> tree like last time.


Can we take this patch atleast for 6.2-rc1?

Thanks,
Sai