[Bug ld/22423] PT_PHDR segment is marked with PF_X

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=22423

--- Comment #2 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Paul Pluzhnikov from comment #1)
> > It was reasonable 20 years ago.
> 
> Normally PT_PHDR overlaps with the first PT_LOAD.
> 
> If you keep that, the flags on PT_PHDR don't matter (the first PT_LOAD will
> have PF_X).
> 
> If you don't keep the overlap, you'll waste an entire page for 64-byte
> PT_PHDR.
> 
> Also, a lot of programs assume that the first PT_LOAD "covers" PT_PHDR and
> starts with ElfW(Ehdr). It's not guaranteed, but it has been true for the
> last 20 years. You'll break all such programs.

My patch does't change the first PT_LOAD permission.  We just have:

Elf file type is EXEC (Executable file)
Entry point 0x8048310
There are 9 program headers, starting at offset 52

Program Headers:
  Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
  PHDR           0x000034 0x08048034 0x08048034 0x00120 0x00120 R   0x4
  INTERP         0x000154 0x08048154 0x08048154 0x00013 0x00013 R   0x1
      [Requesting program interpreter: /lib/ld-linux.so.2]
  LOAD           0x000000 0x08048000 0x08048000 0x005d0 0x005d0 R E 0x1000
  LOAD           0x000f0c 0x08049f0c 0x08049f0c 0x0010c 0x00110 RW  0x1000

Nothing will break.

I am working on -z readonly, which is equivalent to --rosegment for gold.
With -z readonly, I got

Program Headers:
  Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
  PHDR           0x000034 0x00400034 0x00400034 0x00160 0x00160 R   0x4
  INTERP         0x000194 0x00400194 0x00400194 0x0001a 0x0001a R   0x1
      [Requesting program interpreter: /libx32/ld-linux-x32.so.2]
  LOAD           0x000000 0x00400000 0x00400000 0x0037c 0x0037c R   0x200000
  LOAD           0x000e68 0x00600e68 0x00600e68 0x00195 0x00195 R E 0x200000
  LOAD           0x001000 0x00601000 0x00601000 0x0011c 0x0011c R   0x200000
  LOAD           0x200ef0 0x00800ef0 0x00800ef0 0x00134 0x00138 RW  0x200000

It makes permission of PHDR segment the same as the first LOAD segment.
Again, nothing should break.

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