Re: Help needed to track down bug: linking Linux kernel with gold creates unbootable kernel

[John Reiser <jreiser at bitwagon dot com>]

On 04/22/2010 02:10 PM, H.J. Lu wrote:
> On Mon, Apr 12, 2010 at 10:27 PM, Ian Lance Taylor<iant@google.com>  wrote:
> > John Reiser<jreiser@bitwagon.com>  writes:
> >
> > > The differing .p_align values of 0x1000 vs 0x200000 indicate that
> > > gold has a bug interpreting the commands from the linker script
> > > for alignment of Elf64_Phdr.
> >
> > It is perhaps worth noting that for x86_64 gold by default uses -z
> > max-page-size 0x1000 whereas the default for GNU ld is -z
> > max-page-size 0x200000.  While I haven't looked at the Linux linker
> > script, perhaps it is assuming the latter.
>
> Linux kernel linker scripts needs to align .rodata section to 2MB:
>
> . = ALIGN((1<<  21));
>
> Since gold can only align to 4K, gold can't be used on Linux
> kernel.

The linker script statement ". = ALIGN((1<<  21));" requires alignment
to 2 MiB.  If gold "can only align to 4 KiB", then gold must emit an
error message upon processing input that requires a larger alignment.
It is a bug that current gold does not emit such a message for this case.

It seems strange to me that "gold by default uses -z max-page-size 0x1000"
implies "gold cannot align to anything more than 0x1000".  At the minimum,
specifying "-z max-page-size 0x200000" ought to be a workaround here.

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