[Bug ld/19807] New: [2.26 regression] R_386_GOT32X optimization breaks linux kernel

[fvogt at suse dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=19807

            Bug ID: 19807
           Summary: [2.26 regression] R_386_GOT32X optimization breaks
                    linux kernel
           Product: binutils
           Version: 2.27 (HEAD)
            Status: NEW
          Severity: critical
          Priority: P2
         Component: ld
          Assignee: unassigned at sourceware dot org
          Reporter: fvogt at suse dot com
  Target Milestone: ---

Building the i386 linux kernel (tried the latest 4.5 rc7, but all are broken)
with compression causes booting to fail during the decompression stage:
"Failed to allocate space for phdrs".

The kernel decompressor stage is linked to a fixed address, but running at a
different location.
This isn't a problem as it relocates itself by adding the difference to the GOT
entries,
but the optimization "mov $GOTOFF(%ecx), %eax" (R_386_GOT32X) -> "lea $address,
%eax" (R_386_32) breaks this,
as the GOT is no longer referenced in the final ELF.
Result is that some global variables, like free_mem_ptr_end, are overwritten
during decompression, causing weird errors like
malloc returing NULL.

Workaround: specify "--disable-x86-relax-relocations" configure option or
"-mrelax-relocations=no" to as.

See also:
https://bugzilla.opensuse.org/show_bug.cgi?id=970239
https://bugzilla.redhat.com/show_bug.cgi?id=1302071

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