linux-kernel - Re: [PATCH 5/7] printk: Make %pS and friends print module build ID

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Date:   Tue, 02 Mar 2021 15:24:46 -0800
From:   Stephen Boyd <swboyd@...omium.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Jiri Olsa <jolsa@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Jessica Yu <jeyu@...nel.org>,
        Evan Green <evgreen@...omium.org>,
        Hsin-Yi Wang <hsinyi@...omium.org>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH 5/7] printk: Make %pS and friends print module build ID

Quoting Steven Rostedt (2021-03-01 18:43:19)
> On Mon,  1 Mar 2021 09:47:47 -0800
> Stephen Boyd <swboyd@...omium.org> wrote:
> 
> > The %pS printk format (among some others) is used to print kernel
> > addresses symbolically. When the kernel prints an address inside of a
> > module, the kernel prints the addresses' symbol name along with the
> > module's name that contains the address. Let's make kernel stacktraces
> > easier to identify on KALLSYMS builds by including the build ID of a
> > module when we print the address.
> 
> Please no!
> 
> This kills the output of tracing with offset, and can possibly break
> scripts. I don't want to look at traces like this!
> 
>           <idle>-0       [004] ..s1   353.842577: ipv4_conntrack_in+0x0/0x10 [nf_conntrack] (3b39eb771b2566331887f671c741f90bfba0b051) <-nf_hook_slow+0x40/0xb0
>           <idle>-0       [004] ..s1   353.842577: nf_conntrack_in+0x0/0x5c0 [nf_conntrack] (3b39eb771b2566331887f671c741f90bfba0b051) <-nf_hook_slow+0x40/0xb0
>           <idle>-0       [004] ..s1   353.842577: get_l4proto+0x0/0x190 [nf_conntrack] (3b39eb771b2566331887f671c741f90bfba0b051) <-nf_conntrack_in+0x92/0x5c0 [nf_conntrack] (3b39eb771b2566331887f671c741f90bfba0b051)
>           <idle>-0       [004] ..s1   353.842577: nf_ct_get_tuple+0x0/0x240 [nf_conntrack] (3b39eb771b2566331887f671c741f90bfba0b051) <-nf_conntrack_in+0xec/0x5c0 [nf_conntrack] (3b39eb771b2566331887f671c741f90bfba0b051)
>           <idle>-0       [004] ..s1   353.842577: hash_conntrack_raw+0x0/0x170 [nf_conntrack] (3b39eb771b2566331887f671c741f90bfba0b051) <-nf_conntrack_in+0x28c/0x5c0 [nf_conntrack] (3b39eb771b2566331887f671c741f90bfba0b051)
>           <idle>-0       [004] ..s1   353.842578: __nf_conntrack_find_get.isra.0+0x0/0x2f0 [nf_conntrack] (3b39eb771b2566331887f671c741f90bfba0b051) <-nf_conntrack_in+0x29d/0x5c0 [nf_conntrack] (3b39eb771b2566331887f671c741f90bfba0b051)
>           <idle>-0       [004] ..s1   353.842578: nf_conntrack_tcp_packet+0x0/0x1760 [nf_conntrack] (3b39eb771b2566331887f671c741f90bfba0b051) <-nf_conntrack_in+0x3c8/0x5c0 [nf_conntrack] (3b39eb771b2566331887f671c741f90bfba0b051)
>           <idle>-0       [004] ..s2   353.842578: nf_ct_seq_offset+0x0/0x40 [nf_conntrack] (3b39eb771b2566331887f671c741f90bfba0b051) <-nf_conntrack_tcp_packet+0x26d/0x1760 [nf_conntrack] (3b39eb771b2566331887f671c741f90bfba0b051)
>           <idle>-0       [004] ..s1   353.842578: __nf_ct_refresh_acct+0x0/0x50 [nf_conntrack] (3b39eb771b2566331887f671c741f90bfba0b051) <-nf_conntrack_tcp_packet+0x558/0x1760 [nf_conntrack] (3b39eb771b2566331887f671c741f90bfba0b051)
> 
>  NACK!
> 

Heh, OK. Would adding a new printk format work then? From after the cut:

> Yet another alternative is to add a printk format like %pSB for
> backtrace prints. This would require a handful of architecture updates
> and I'm not sure it's worth the effort for that.
>

Or maybe take the approach of putting all the linked in module build IDs
in the "Modules linked in:" section? But as I said in the commit text
that can become quite verbose. Looking forward to your suggestions here.