[Bug libdw/28720] UBSan: member access within misaligned address 0x7f6e8d80f142 for type 'struct Elf32_Phdr', which requires 4 byte alignment

["evvers at ya dot ru" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=28720

--- Comment #3 from Evgeny Vereshchagin <evvers at ya dot ru> ---
As far as I can see with the fuzz branch rebased on top on my fuzzing branch
almost all the issues including
https://sourceware.org/pipermail/elfutils-devel/2021q4/004596.html are gone.
Thanks! I'll attach files triggering the remaining issues shortly:
```
$ UBSAN_OPTIONS=print_stacktrace=1:print_summary=1:halt_on_error=1
LD_LIBRARY_PATH="./libdw;./libelf" ./src/stack --core
SIGABRT.PC.7fffe4f4e84c.STACK.18f0f46b60.CODE.-6.ADDR.0.INSTR.mov____%eax,%ebp.fuzz
link_map.c:1040:20: runtime error: variable length array bound evaluates to
non-positive value 0
    #0 0x7fbc58f053e9 in dwfl_link_map_report
/home/vagrant/elfutils/libdwfl/link_map.c:1040
    #1 0x7fbc59023fa7 in _new.dwfl_core_file_report
/home/vagrant/elfutils/libdwfl/core-file.c:552
    #2 0x4053f7 in parse_opt /home/vagrant/elfutils/src/stack.c:595
    #3 0x7fbc581d9471 in argp_parse (/lib64/libc.so.6+0x11e471)
    #4 0x404b39 in main /home/vagrant/elfutils/src/stack.c:695
    #5 0x7fbc580e855f in __libc_start_call_main (/lib64/libc.so.6+0x2d55f)
    #6 0x7fbc580e860b in __libc_start_main_impl (/lib64/libc.so.6+0x2d60b)
    #7 0x404fa4 in _start (/home/vagrant/elfutils/src/stack+0x404fa4)

SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior link_map.c:1040:20 in
```
```
$ UBSAN_OPTIONS=print_stacktrace=1:print_summary=1:halt_on_error=1
LD_LIBRARY_PATH="./libdw;./libelf" ./src/stack --core
SIGABRT.PC.7fffe4f4e84c.STACK.1976b2f3ff.CODE.-6.ADDR.0.INSTR.mov____%eax,%ebp.fuzz
gelf_xlate.h:48:1: runtime error: member access within misaligned address
0x7f0817719077 for type 'struct Elf32_Dyn', which requires 4 byte alignment
0x7f0817719077: note: pointer points here
 00 10 00 00 00  00 00 00 00 00 02 01 00  00 00 00 00 00 7f 45 46  4c 46 00 00
01 01 00 01  00 08 00
             ^
    #0 0x7f0822689542 in Elf32_cvt_Dyn
/home/vagrant/elfutils/libelf/gelf_xlate.h:48
    #1 0x7f082268835e in elf32_xlatetom
/home/vagrant/elfutils/libelf/elf32_xlatetom.c:104
    #2 0x7f0819563307 in dwfl_segment_report_module
/home/vagrant/elfutils/libdwfl/dwfl_segment_report_module.c:848
    #3 0x7f081956c06c in _new.dwfl_core_file_report
/home/vagrant/elfutils/libdwfl/core-file.c:563
    #4 0x4053f7 in parse_opt /home/vagrant/elfutils/src/stack.c:595
    #5 0x7f0818721471 in argp_parse (/lib64/libc.so.6+0x11e471)
    #6 0x404b39 in main /home/vagrant/elfutils/src/stack.c:695
    #7 0x7f081863055f in __libc_start_call_main (/lib64/libc.so.6+0x2d55f)
    #8 0x7f081863060b in __libc_start_main_impl (/lib64/libc.so.6+0x2d60b)
    #9 0x404fa4 in _start (/home/vagrant/elfutils/src/stack+0x404fa4)

SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior gelf_xlate.h:48:1 in
```

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