This is a reproducer for issues with feeding libdwfl the perf mmap events, cf. KDAB/hotspot#125

To use it, first run perf on an application of your choice:

    $ perf record --call-graph dwarf <...>

Now create a text file with all the mmap events in the perf data file:

    $ perf script -show-mmap-events | grep PERF_RECORD_MMAP2 > mmaps.txt

Then feed this file into the reproducer:

    $ ./perf_mmaps_to_elfutils mmaps.txt

You should notice some discrepandcies between actual mmap events and what libdwfl sees.

Example:

```
0x5560be12d000 to 0x5560be132000, len =     0x5000, offset =                0   r--p    /home/milian/projects/kdab/rnd/hotspot/build/tests/test-clients/cpp-inlining/cpp-inlining
0x5560be12e000 to 0x5560be12f000, len =     0x1000, offset =           0x1000   r-xp    /home/milian/projects/kdab/rnd/hotspot/build/tests/test-clients/cpp-inlining/cpp-inlining
0x5560be12f000 to 0x5560be130000, len =     0x1000, offset =           0x2000   r--p    /home/milian/projects/kdab/rnd/hotspot/build/tests/test-clients/cpp-inlining/cpp-inlining
0x5560be130000 to 0x5560be132000, len =     0x2000, offset =           0x2000   rw-p    /home/milian/projects/kdab/rnd/hotspot/build/tests/test-clients/cpp-inlining/cpp-inlining
0x7fac5ede7000 to 0x7fac5ee13000, len =    0x2c000, offset =                0   r--p    /usr/lib/ld-2.28.so
0x7fac5ede9000 to 0x7fac5ee08000, len =    0x1f000, offset =           0x2000   r-xp    /usr/lib/ld-2.28.so
0x7fac5ee08000 to 0x7fac5ee10000, len =     0x8000, offset =          0x21000   r--p    /usr/lib/ld-2.28.so
0x7fac5ee10000 to 0x7fac5ee12000, len =     0x2000, offset =          0x28000   rw-p    /usr/lib/ld-2.28.so
0x7fac5ec0b000 to 0x7fac5ed9a000, len =   0x18f000, offset =                0   r--p    /usr/lib/libstdc++.so.6.0.25
0x7fac5ec94000 to 0x7fac5ed8a000, len =    0xf6000, offset =          0x89000   ---p    /usr/lib/libstdc++.so.6.0.25
0x7fac5ec94000 to 0x7fac5ed4c000, len =    0xb8000, offset =          0x89000   r-xp    /usr/lib/libstdc++.so.6.0.25
0x7fac5ed4c000 to 0x7fac5ed89000, len =    0x3d000, offset =         0x141000   r--p    /usr/lib/libstdc++.so.6.0.25
0x7fac5ed8a000 to 0x7fac5ed97000, len =     0xd000, offset =         0x17e000   rw-p    /usr/lib/libstdc++.so.6.0.25
...

reported module /home/milian/projects/kdab/rnd/hotspot/build/tests/test-clients/cpp-inlining/cpp-inlining
        expected: 0x5560be12d000@0 to 0x5560be132000 (0x5000)
        actual:   0x5560be12d000@0 to 0x5560be131178 (0x4178)
        dwbias:   0xffffffffffffffff, symbias:0xffffffffffffffff
        mainfile: /home/milian/projects/kdab/rnd/hotspot/build/tests/test-clients/cpp-inlining/cpp-inlining
        dbgfile:  <no debug file>
LEN MISMATCH! 5000 VS 4178, diff: -3720
skipping (pgoff != 0): /home/milian/projects/kdab/rnd/hotspot/build/tests/test-clients/cpp-inlining/cpp-inlining        1000
skipping (pgoff != 0): /home/milian/projects/kdab/rnd/hotspot/build/tests/test-clients/cpp-inlining/cpp-inlining        2000
skipping (pgoff != 0): /home/milian/projects/kdab/rnd/hotspot/build/tests/test-clients/cpp-inlining/cpp-inlining        2000
reported module /usr/lib/ld-2.28.so
        expected: 0x7fac5ede7000@0 to 0x7fac5ee13000 (0x2c000)
        actual:   0x7fac5ede7000@0 to 0x7fac5ee12118 (0x2b118)
        dwbias:   0xffffffffffffffff, symbias:0xffffffffffffffff
        mainfile: /usr/lib/ld-2.28.so
        dbgfile:  <no debug file>
LEN MISMATCH! 2c000 VS 2b118, diff: -3816
skipping (pgoff != 0): /usr/lib/ld-2.28.so      2000
skipping (pgoff != 0): /usr/lib/ld-2.28.so      21000
skipping (pgoff != 0): /usr/lib/ld-2.28.so      28000
reported module /usr/lib/libstdc++.so.6.0.25
        expected: 0x7fac5ec0b000@0 to 0x7fac5ed9a000 (0x18f000)
        actual:   0x7fac5ec0b000@0 to 0x7fac5ed99640 (0x18e640)
        dwbias:   0xffffffffffffffff, symbias:0xffffffffffffffff
        mainfile: /usr/lib/libstdc++.so.6.0.25
        dbgfile:  <no debug file>
LEN MISMATCH! 18f000 VS 18e640, diff: -2496
skipping (pgoff != 0): /usr/lib/libstdc++.so.6.0.25     89000
skipping (pgoff != 0): /usr/lib/libstdc++.so.6.0.25     89000
skipping (pgoff != 0): /usr/lib/libstdc++.so.6.0.25     141000
skipping (pgoff != 0): /usr/lib/libstdc++.so.6.0.25     17e000
...
```

Additional information:

```
$ eu-readelf -l /usr/lib/libstdc++.so.6.0.25
Program Headers:
  Type           Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align
  LOAD           0x000000 0x0000000000000000 0x0000000000000000 0x088fa8 0x088fa8 R   0x1000
  LOAD           0x089000 0x0000000000089000 0x0000000000089000 0x0b7ae1 0x0b7ae1 R E 0x1000
  LOAD           0x141000 0x0000000000141000 0x0000000000141000 0x03cfe0 0x03cfe0 R   0x1000
  LOAD           0x17e8e0 0x000000000017f8e0 0x000000000017f8e0 0x00b8b8 0x00ed60 RW  0x1000
  DYNAMIC        0x1873a8 0x00000000001883a8 0x00000000001883a8 0x0001e0 0x0001e0 RW  0x8
  NOTE           0x0002a8 0x00000000000002a8 0x00000000000002a8 0x000024 0x000024 R   0x4
  NOTE           0x17dfc0 0x000000000017dfc0 0x000000000017dfc0 0x000020 0x000020 R   0x8
  TLS            0x17e8e0 0x000000000017f8e0 0x000000000017f8e0 0x000000 0x000020 R   0x8
  GNU_EH_FRAME   0x149558 0x0000000000149558 0x0000000000149558 0x007f04 0x007f04 R   0x4
  GNU_STACK      0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 RW  0x10
  GNU_RELRO      0x17e8e0 0x000000000017f8e0 0x000000000017f8e0 0x00b720 0x00b720 R   0x1

 Section to Segment mapping:
  Segment Sections...
   00      [RO: .note.gnu.build-id .gnu.hash .dynsym .dynstr .gnu.version .gnu.version_d .gnu.version_r .rela.dyn]
   01      [RO: .init .text .fini]
   02      [RO: .rodata .eh_frame_hdr .eh_frame .gcc_except_table .note.gnu.property]
   03      [RELRO: .tbss .init_array .fini_array .data.rel.ro .dynamic .got] .got.plt .data .bss
   04      [RELRO: .dynamic]
   05      [RO: .note.gnu.build-id]
   06      [RO: .note.gnu.property]
   07      [RELRO: .tbss]
   08      [RO: .eh_frame_hdr]
   09     
   10      [RELRO: .tbss .init_array .fini_array .data.rel.ro .dynamic .got]
```