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From:   Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Date:   Fri, 20 Sep 2019 16:38:52 -0300
To:     Steve MacLean <Steve.MacLean@microsoft.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Changbin Du <changbin.du@intel.com>,
        Eric Saint-Etienne <eric.saint.etienne@oracle.com>,
        John Keeping <john@metanate.com>,
        Andi Kleen <ak@linux.intel.com>,
        Song Liu <songliubraving@fb.com>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Leo Yan <leo.yan@linaro.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Brian Robbins <brianrob@microsoft.com>,
        Tom McDonald <Thomas.McDonald@microsoft.com>,
        John Salem <josalem@microsoft.com>
Subject: Re: [PATCH] perf map: fix overlapped map handling
Message-ID: <20190920193852.GI4865@kernel.org>
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Em Fri, Sep 20, 2019 at 07:20:18PM +0000, Steve MacLean escreveu:
> Whenever an mmap/mmap2 event occurs, the map tree must be updated to add a new
> entry. If a new map overlaps a previous map, the overlapped section of the
> previous map is effectively unmapped, but the non-overlapping sections are
> still valid.
> 
> maps__fixup_overlappings() is responsible for creating any new map entries from
> the previously overlapped map. It optionally creates a before and an after map.
> 
> When creating the after map the existing code failed to adjust the map.pgoff.
> This meant the new after map would incorrectly calculate the file offset
> for the ip. This results in incorrect symbol name resolution for any ip in the
> after region.
> 
> Make maps__fixup_overlappings() correctly populate map.pgoff.
> 
> Add an assert that new mapping matches old mapping at the beginning of
> the after map.
> 
> Signed-off-by: Steve MacLean <Steve.MacLean@Microsoft.com>
> ---
>  tools/perf/util/map.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/tools/perf/util/map.c b/tools/perf/util/map.c
> index 5b83ed1..73870d7 100644
> --- a/tools/perf/util/map.c
> +++ b/tools/perf/util/map.c
> @@ -1,5 +1,6 @@
>  // SPDX-License-Identifier: GPL-2.0
>  #include "symbol.h"
> +#include <assert.h>
>  #include <errno.h>
>  #include <inttypes.h>
>  #include <limits.h>
> @@ -850,6 +851,8 @@ static int maps__fixup_overlappings(struct maps *maps, struct map *map, FILE *fp
>  			}
>  
>  			after->start = map->end;
> +			after->pgoff = pos->map_ip(pos, map->end);

So is this equivalent to what __split_vma() does in the kernel, i.e.:

        if (new_below)
                new->vm_end = addr;
        else {
                new->vm_start = addr;
                new->vm_pgoff += ((addr - vma->vm_start) >> PAGE_SHIFT);
        }

where new->vm_pgoff starts equal to the vm_pgoff of the mmap being
split?

- Arnaldo

> +			assert(pos->map_ip(pos, map->end) == after->map_ip(after, map->end));


>  			__map_groups__insert(pos->groups, after);
>  			if (verbose >= 2 && !use_browser)
>  				map__fprintf(after, fp);
> -- 
> 2.7.4

-- 

- Arnaldo