[Bug target/63833] New: REAL_PIC_OFFSET_TABLE_REGNUM is wrong for x86-64

[hjl.tools at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63833

            Bug ID: 63833
           Summary: REAL_PIC_OFFSET_TABLE_REGNUM is wrong for x86-64
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hjl.tools at gmail dot com
                CC: ubizjak at gmail dot com
            Target: x86_64-linux

x86-64 psABI uses %r15 to hold the GOT base pointer in large model.
The first entry in the large model PLT is

PLT0: pushq 8(%r15)   # GOT[1]
      jmpq  *16(%r15) # GOT[2]

However, there is a typo in Register Usage table in x86-64 psABI:

%rbx  callee-saved register; optionally used as base pointer

Using %rbx for GOT will crash the large model PLT.  It should be

%rbx  callee-saved register
...
%r15  callee-saved register; optionally used as GOT base pointer

I proposed a change to Register Usage table in x86-64 psABI:

https://gcc.gnu.org/ml/gcc/2014-11/msg00161.html