Fix regression for Linux vDSO in GDB (PR gdb/17407).

Fix regression for Linux vDSO in GDB (PR gdb/17407).

since
	5979d6b69b20a8355ea94b75fad97415fce4788c
	https://sourceware.org/git/?p=binutils-gdb.git;a=commitdiff;h=5979d6b69b20a8355ea94b75fad97415fce4788c
	vdso handling
	https://sourceware.org/ml/binutils/2014-03/msg00082.html
	https://sourceware.org/ml/binutils/2014-04/msg00003.html
	Message-ID: <A78C989F6D9628469189715575E55B230AA884EB@IRSMSX104.ger.corp.intel.com>
I get on
	kernel-3.16.2-200.fc20.x86_64
	https://koji.fedoraproject.org/koji/buildinfo?buildID=575860
	attaching its vdso.bin.gz
GDB (FSF HEAD 5e43d46791c4c66fd83947a12d4f716b561a9103) regression:
reproducer:
	./gdb -ex start ./gdb
actual result / FAIL:
	Got object file from memory but can't read symbols: File truncated.
expected result / PASS:
	<nothing>
or / PASS:
	warning: Could not load shared library symbols for linux-vdso.so.1.
	Do you need "set solib-search-path" or "set sysroot"?

That "warning: Could not load shared library..." is mostly harmless (it is
a bug in GDB), in the FAIL case it is not printed just because
bfd_check_format() fails there.

It seems logical to me this way when the 'size' parameter has been already
added.
Alan Modra:
I was wrongly thinking that the section headers were
always last when I wrote that code.  (They are now!  If you relink
that vdso with current binutils master you won't hit this problem, but
that of course doesn't help existing kernels.)

I do not see a regression for add-symbol-file-from-memory for libncurses.so.5
from the original thread above.

  Start of section headers:          1080 (bytes into file)
  Size of section headers:           64 (bytes)
  Number of section headers:         13
  Section header string table index: 8
Section Headers:
  [Nr] Name              Type            Address          Off    Size   ES Flg Lk Inf Al
  [ 8] .fake_shstrtab    STRTAB          0000000000000780 000780 000076 00   A  0   0 32
Program Headers:
  Type           Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align
  LOAD           0x000000 0x0000000000000000 0x0000000000000000 0x0012fe 0x0012fe R E 0x1000

size == 0x2000
shdr_end == 0x778 == 1080 + 13 * 64
high_offset == 0x12fe

       else if (size >= shdr_end)
-	high_offset = shdr_end;
+	high_offset = size;

But then 0x778 < 0x780 for "Section header string table index" so whole
bfd_check_format() fails because section headers were not cleared here:
  /* If the segments visible in memory didn't include the section headers,
     then clear them from the file header.  */
  if (high_offset < shdr_end)

bfd/ChangeLog
2014-09-18  Jan Kratochvil  <jan.kratochvil@redhat.com>

	PR gdb/17407
	* elfcode.h (bfd_from_remote_memory): Use SIZE for HIGH_OFFSET.