Re: [binutils-gdb] Fix the linker so that it will not silently generate ELF binaries with invalid program headers. Fix

[Alan Modra <amodra at gmail dot com>]

On Thu, Dec 08, 2016 at 09:30:04AM +0000, Maciej W. Rozycki wrote:
> Program Headers:
>   Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
>   PHDR           0x000034 0x00001034 0x00000000 0x000a0 0x000a0 R E 0x4
>   INTERP         0x001000 0x00080000 0x00080000 0x00013 0x00013 R   0x1
>       [Requesting program interpreter: /usr/lib/libc.so.1]
>   LOAD           0x001000 0x00080000 0x00080000 0x00408 0x00408 R E 0x1000
>   LOAD           0x002000 0x00081000 0x00081000 0x00804 0x00c00 RW  0x1000
>   DYNAMIC        0x002000 0x00081000 0x00081000 0x00078 0x00078 RW  0x4

The gABI says:

PT_PHDR
    The array element, if present, specifies the location and size of
    the program header table itself, both in the file and in the
    memory image of the program. This segment type may not occur more
    than once in a file. Moreover, it may occur only if the program
    header table is part of the memory image of the program. If it is
    present, it must precede any loadable segment entry.

The above clearly violates this part of the spec because PT_PHDR is
present yet is not part of the memory image.

Nick's patch forced the first PT_LOAD to cover the program headers.  I
think an equally valid and somewhat better fix would have been to not
emit PT_PHDR when no PT_LOAD header covers the program headers.  The
reason I say that is because PT_PHDR is optional.  A loader can read
the program headers itself from file using info in the ELF header.

-- 
Alan Modra
Australia Development Lab, IBM