GNU hash-style compatibility problem on x86_64

[Greg Schafer <gschafer at zip dot com dot au>]

Hi,

Host platform is current x86_64:

  HJL binutils-2.17.50.0.18
  gcc-4.2.1
  glibc-2.6.1 (glibc defaults to compiling with --hash-style=both)

The problem strikes on this host when attempting to natively bootstrap an
older toolchain (eg: with FSF binutils-2.17):

$ echo 'main(){}' | stage1/xgcc -Bstage1/ -xc -o /dev/null -
/lib64/libc.so.6: file not recognized: File format not recognized
collect2: ld returned 1 exit status

Essentially, the older ld chokes on the newer libc ie: the one compiled with
--hash-style=both (it affects any dso with --hash-style=gnu actually).

The weird thing is, it only happens on x86_64. I've tested the exact same
scenario on x86 and ppc and those arches both work fine. Why should x86_64
behave any differently here? This is all above my head so I would really
appreciate your help in understanding the root cause.

You should be able to easily reproduce this if your x86_64 host has a libc
that was compiled with --hash-style=both (latest Fedora, Debian lenny etc),
just build binutils-2.17 then try to link using its ld. Note: you might have
to fiddle with gcc specs if your host gcc is hardwired for --hash-style=gnu

Thanks
Greg

(yes, I could just use a newer binutils, or even cross compile, but that's
not the point)