linux-kernel - Re: [PATCH] perf tools: set kernel end address properly

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Date:   Thu, 19 Apr 2018 18:20:24 -0500
From:   Kim Phillips <kim.phillips@....com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Jiri Olsa <jolsa@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, <kernel-team@....com>
Subject: Re: [PATCH] perf tools: set kernel end address properly

On Thu, 19 Apr 2018 11:37:12 +0900
Namhyung Kim <namhyung@...nel.org> wrote:

> On Wed, Apr 18, 2018 at 07:37:59PM -0500, Kim Phillips wrote:
> > On Tue, 17 Apr 2018 11:27:26 +0900
> > Namhyung Kim <namhyung@...nel.org> wrote:
> > > On Mon, Apr 16, 2018 at 05:48:11PM -0500, Kim Phillips wrote:
> > > > > a perf/urgent from last week (commit 918965d4897) + this patch:
> > > > > 
> > > > > $ sudo ./perf test -vv 1 |& head 
> > > > >  1: vmlinux symtab matches kallsyms                       :
> > > > > --- start ---
> > > > > test child forked, pid 6194
> > > > > Looking at the vmlinux_path (8 entries long)
> > > > > Using /lib/modules/4.16.0+/build/vmlinux for symbols
> > > > > ERR : 0xffff200008081000: do_undefinstr not on kallsyms
> > > > > ERR : 0xffff2000080810b8: do_sysinstr not on kallsyms
> > > > > ERR : 0xffff200008081258: do_debug_exception not on kallsyms
> > > > > ERR : 0xffff200008081648: do_mem_abort not on kallsyms
> > > > > ERR : 0xffff2000080818b8: do_el0_irq_bp_hardening not on kallsyms
> > > > > $ sudo ./perf test -vv 1 |& tail
> > > > > ERR : 0xffff20000a1d37c8: tramp_exit_native not on kallsyms
> > > > > ERR : 0xffff20000a1d37e8: tramp_exit_compat not on kallsyms
> > > > > ERR : 0xffff20000a1d4000: __entry_tramp_text_end not on kallsyms
> > > > > WARN: Maps only in vmlinux:
> > > > >  ffff200008080000-ffff200008081000 10000 [kernel].head.text
> > > > >  ffff20000aec0000-ffff20000aff7548 2e50000 [kernel].init.text
> > > > >  ffff20000aff7548-ffff20000b0126d4 2f87548 [kernel].exit.text
> > > > > test child finished with -1
> > > > > ---- end ----
> > > > > vmlinux symtab matches kallsyms: FAILED!
> > > > 
> > > > this patch's advertised "If there's no module after the kernel map, the
> > > > end address will be ~0ULL." doesn't seem to be working: the value it
> > > > gets for 'end' is 0xffff200008080000.
> > > 
> > > For the vmlinux, right?
> > 
> > yes, map__next(machine__kernel_map(machine)) has the start address
> > of the single module currently loaded:
> > 
> > ffff200002290000 t $x	[arm_ccn]
> > ffff200002290000 t arm_ccn_pmu_events_is_visible	[arm_ccn]
> > 
> > The beginning of the kernel is..later:
> > 
> > ffff200008080000 t _head
> > ffff200008080000 T _text
> > 
> > and its end according to grep -w _end /proc/kallsyms is:
> > 
> > ffff20000d5f9000 B _end
> > 
> > but end was assigned to the beginning of arm_ccn (0xffff200002290000),
> > which is upside-down.
> 
> So ARM64 has modules below the kernel.

right.

> > > To be precise, it should be "If there's no map after the kernel map".
> > 
> > In numerical address order, in maps in map_groups__insert order, or
> > some other order?
> 
> The map_groups__insert() also sorts the map by address, so they should

Had missed that, sorry.

> be identical.  I think the problem is perf assumes the kernel is the
> first map in the kmaps.  When it calls maps_groups__insert() it uses
> start address of 0 for the kernel map.  It seems always true for x86
> but not for ARM64.
> 
> While it changes the start address in machine__set_kernel_mmap() it
> doesn't change the order in the kmaps.
> 
> Could you please test below patch (on top) then?

Much better, thank you!  Together with the "module_emit_adrp_veneer not
on kallsyms" mitigation diff, test 1 now passes on arm64 systems both
with modules loaded, and without, and with and without RANDOMIZE_BASE.

I would send a patch (From: you), but I think you'd do a better job on
writing the commit text, so would you care to, please?

Thanks,

Kim