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

[Sai Prakash Ranjan]

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.

Thanks,
Sai