Re: gold patch committed (Was: Re: Help needed to track down bug: linking Linux kernel with gold creates unbootable kernel)

[Ian Lance Taylor <iant at google dot com>]

"H.J. Lu" <hjl.tools@gmail.com> writes:

> On Fri, Apr 23, 2010 at 8:16 AM, Ian Lance Taylor <iant@google.com> wrote:
>> "H.J. Lu" <hjl.tools@gmail.com> writes:
>>
>>> Program Headers:
>>>  Type      Offset       VirtAddr      PhysAddr
>>>         ÂFileSiz      ÂMemSiz       ÂFlags ÂAlign
>>> Â LOAD Â Â Â Â Â 0x0000000000001000 0x0000000000000000 0x0000000000000000
>>> Â Â Â Â Â Â Â Â Â0x0000000000000001 0x0000000000000001 ÂR E Â Â1000
>>> Â LOAD Â Â Â Â Â 0x0000000000002000 0x0000000000004000 0x0000000000004000
>>> Â Â Â Â Â Â Â Â Â0x0000000000002001 0x0000000000002001 ÂRW Â Â 4000
>>
>> This looks right to me.
>>
>>
>>> I am not sure it is a good idea to have different p_align.
>>
>> Why not? ÂHow else can we communicate the information requested by the
>> programmer? ÂA system which cares about p_align needs to look at the
>> p_align of each PT_LOAD header.
>
> You can't load the first segment with 0x1000 alignment. You
> need to load the first segment with the alignment of the second
> segment. Why does gold have to make life harder for loader?

The Linux kernel doesn't look at the p_align field, nor should it.
The p_align field is clearly irrelevant when loading an executable.
The glibc dynamic linker checks that the p_align field looks
plausible, but otherwise ignores it other than for a PT_TLS segment;
that seems appropriate since ld.so is restricted to what mmap does
anyhow.  In general, it's hard for me to think of why any loader on a
virtual memory system would look at the p_align field.  And it's hard
for to think of any non-virtual memory system that would support ELF
style shared libraries.

So I think you are raising a purely hypothetical concern.

On the other hand the p_align field does convey information about the
sections in that particular segment, and that seems reasonable to me.

Ian