Re: [RFC PATCH v2 2/3] pstore: Add register read/write{b,w,l,q} tracing support

[Kees Cook]

On Fri, Aug 24, 2018 at 7:45 AM, Sai Prakash Ranjan
<saiprakash.ranjan@xxxxxxxxxxxxxx> wrote:
> read/write{b,w,l,q} are typically used for reading from memory
> mapped registers, which can cause hangs if accessed
> unclocked. Tracing these events can help in debugging
> various issues faced during initial development.
>
> We log this trace information in persistent ram buffer which
> can be viewed after reset.
>
> We use pstore_rtb_call() to write the RTB log to pstore.
> RTB buffer size is taken from ramoops dt node with additional
> property called rtb-size.
>
> For reading the trace after mounting pstore, rtb-ramoops entry
> can be seen in /sys/fs/pstore/ as in below sample output.
>
> Sample output of tracing register reads/writes in drivers:
>
>  # mount -t pstore pstore /sys/fs/pstore
>  # tail /sys/fs/pstore/rtb-ramoops-0
>  [LOGK_READ ] ts:36468476204  data:ffff00000800d0fc  <ffff0000084e9ee0>  gic_check_gicv2+0x58/0x60
>  [LOGK_WRITE] ts:36468477715  data:ffff00000800d000  <ffff0000084e9fac>  gic_cpu_if_up+0xc4/0x110
>  [LOGK_READ ] ts:36468478548  data:ffff00000800d000  <ffff0000084e9fd8>  gic_cpu_if_up+0xf0/0x110
>  [LOGK_WRITE] ts:36468480319  data:ffff00000800d000  <ffff0000084e9fac>  gic_cpu_if_up+0xc4/0x110
>  [LOGK_READ ] ts:36468481048  data:ffff00000800d00c  <ffff000008081a34>  gic_handle_irq+0xac/0x128
>  [LOGK_WRITE] ts:36468482923  data:ffff00000800d010  <ffff000008081aac>  gic_handle_irq+0x124/0x128
>  [LOGK_READ ] ts:36468483184  data:ffff00000800d00c  <ffff000008081a34>  gic_handle_irq+0xac/0x128
>  [LOGK_WRITE] ts:36468485215  data:ffff00000800d010  <ffff000008081aac>  gic_handle_irq+0x124/0x128
>  [LOGK_READ ] ts:36468486309  data:ffff00000800d00c  <ffff000008081a34>  gic_handle_irq+0xac/0x128
>  [LOGK_WRITE] ts:36468488236  data:ffff00000800d010  <ffff000008081aac>  gic_handle_irq+0x124/0x128
>
> Output has below 5 fields:
>
>  * Log type, Timestamp, Data from caller which is the address of
>    read/write{b,w,l,q}, Caller ip and Caller name.
>
> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>

As this is a tracing-like method, could this instead be added to
ftrace? That would mean it could reuse all the ftrace tools and you'd
get pstore storage for free.

-Kees

-- 
Kees Cook
Pixel Security