gold patch committed (Was: Re: Help needed to track down bug: linking Linux kernel with gold creates unbootable kernel)
H.J. Lu
hjl.tools@gmail.com
Fri Apr 23 17:57:00 GMT 2010
On Fri, Apr 23, 2010 at 8:49 AM, Ian Lance Taylor <iant@google.com> wrote:
> "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
>>>> FileSiz MemSiz Flags Align
>>>> LOAD 0x0000000000001000 0x0000000000000000 0x0000000000000000
>>>> 0x0000000000000001 0x0000000000000001 R E 1000
>>>> LOAD 0x0000000000002000 0x0000000000004000 0x0000000000004000
>>>> 0x0000000000002001 0x0000000000002001 RW 4000
>>>
>>> This looks right to me.
>>>
>>>
>>>> I am not sure it is a good idea to have different p_align.
>>>
>>> Why not? How else can we communicate the information requested by the
>>> programmer? A 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.
>
See:
http://www.sourceware.org/bugzilla/show_bug.cgi?id=11533
--
H.J.
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