[Bug tools/28873] Implement eu-readelf -D

["dichen at redhat dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=28873

--- Comment #5 from Di Chen <dichen at redhat dot com> ---
Created attachment 14600
  --> https://sourceware.org/bugzilla/attachment.cgi?id=14600&action=edit
readelf: display dynamic symtab without section headers

```
# failed to print symtab of a binary which has section headers removed.
$ ./src/readelf -s ~/test/a.out

# it works with "-D" for a binary which has section headers removed.
$ ./src/readelf -Ds ~/test/a.out 
    0: 0000000000000000      0 NOTYPE  LOCAL  DEFAULT    UNDEF 
    1: 0000000000000000      0 FUNC    GLOBAL DEFAULT    UNDEF
__libc_start_main@GLIBC_2.34 (2)
    2: 0000000000000000      0 NOTYPE  WEAK   DEFAULT    UNDEF __gmon_start__
```

It works well for binaries which has SYMTAB section right after STRTAB section.
```
$ readelf -Dd ~/test/a.out 

Dynamic section at offset 0x2e60 contains 20 entries:
  Tag        Type                         Name/Value
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]
 0x000000000000000c (INIT)               0x401000
 0x000000000000000d (FINI)               0x401124
 0x0000000000000019 (INIT_ARRAY)         0x403e50
 0x000000000000001b (INIT_ARRAYSZ)       8 (bytes)
 0x000000000000001a (FINI_ARRAY)         0x403e58
 0x000000000000001c (FINI_ARRAYSZ)       8 (bytes)
 0x000000006ffffef5 (GNU_HASH)           0x4003c0
 0x0000000000000005 (STRTAB)             0x400428
 0x0000000000000006 (SYMTAB)             0x4003e0
 0x000000000000000a (STRSZ)              55 (bytes)
 0x000000000000000b (SYMENT)             24 (bytes)
 0x0000000000000015 (DEBUG)              0x0
 0x0000000000000007 (RELA)               0x400488
 0x0000000000000008 (RELASZ)             48 (bytes)
 0x0000000000000009 (RELAENT)            24 (bytes)
 0x000000006ffffffe (VERNEED)            0x400468
 0x000000006fffffff (VERNEEDNUM)         1
 0x000000006ffffff0 (VERSYM)             0x400460
 0x0000000000000000 (NULL)               0x0
```
Because I use offset difference between SYMTAB and STRTAB to get the symbol
table entry number.
```
  size_t syments = ((offs[i_strtab] - offs[i_symtab]) /
    gelf_fsize(ebl->elf, ELF_T_SYM, 1, EV_CURRENT));
```

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