binutils/ld: "Sort relocs output by ld -r" breaks mips cross compilation of linux
Tue Dec 9 07:29:00 GMT 2014
On Tue, Dec 9, 2014 at 2:21 AM, Alan Modra <email@example.com> wrote:
> On Mon, Dec 08, 2014 at 03:33:45PM +0000, Andrew Bennett wrote:
>> > your patch to binutils/ld "Sort relocs output by ld -r" causes a lot of
>> > the following warnings when I cross-compile the linux kernel for
>> > little-endian mips32 on an x64 host:
>> > mipsel-softfloat-linux-gnu-ld: init/mounts.o: Can't find matching LO16
>> > reloc against `$LC2' for R_MIPS_HI16 at 0x4e8 in section `.text'
>> > If I revert that patch the kernel build succeeds without warnings and boots.
>> > (I wrongly blamed a patch by Andrew Bennett before which turns out
>> > to be innocent).
>> It is probably best to explain why this causes the issue, so I have explained
>> it in more detail below:
>> The MIPS HI16/LO16 relocations must occur in pairs. This means the LO16
>> relocation must occur directly after the HI16 relocation in the relocation table.
>> If we look at an example that was found in the Linux build. The original
>> elf file had the relocations in the following order.
>> 00000514 00005f05 R_MIPS_HI16 00000000 block_class
>> 00000458 00005f05 R_MIPS_HI16 00000000 block_class
>> 00000460 00005f06 R_MIPS_LO16 00000000 block_class
>> But these became the following when -r is used:
>> 00000458 00005705 R_MIPS_HI16 00000000 block_class
>> 0000045c 00000305 R_MIPS_HI16 00000000 .text
>> 00000460 00005706 R_MIPS_LO16 00000000 block_class
>> 00000514 00005705 R_MIPS_HI16 00000000 block_class
>> Therefore when the HI16/LO16 relocation checking is done for the block_class
>> symbol it will be unable to find the corresponding LO16 relocation in the
>> second instance, which is why Manuel was getting error messages about
>> missing relocations.
> Blah. I sorted external relocs rather than internal just for mips,
> otherwise a non-stable qsort might reorder within the abominable
> 3-for-1 internal relocs. I didn't remember that mips deliberately
> puts relocs out of r_offset order as per the mips ABI.
> The following ought to fix it. Please review the mips changes and let
> me know if they are good.
This patch works fine, kernel builds and boots.
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