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

From: Kees Cook
Date: Fri Aug 24 2018 - 11:29:54 EST

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 Cook
Pixel Security