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From: "amodra at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/65810] powerpc64 libgfortran alignment issue?
Date: Mon, 20 Apr 2015 05:24:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65810

Alan Modra <amodra at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2015-04-20
           Assignee|unassigned at gcc dot gnu.org      |amodra at gmail dot com
     Ever confirmed|0                           |1

--- Comment #4 from Alan Modra <amodra at gmail dot com> ---
Here's the bad code
   0x00000fffb7f6c438 <write_float+3736>:    addis   r9,r2,-2
   0x00000fffb7f6c43c <write_float+3740>:    li      r27,0
   0x00000fffb7f6c440 <write_float+3744>:    lfd     f24,32760(r9)
   0x00000fffb7f6c444 <write_float+3748>:    lfd     f25,-32768(r9)

It's from write_float.def:888
  r *= 10;
so is supposed to be loading up 10.0L but instead gets a completely bogus low
double as seen in "d" below.
__gcc_qmul (a=1, b=0, c=10, d=-7.3968712249802237e+209)

So not something odd in libgfortran..

Hmm
p/x $r2
$31 = 0xfffb7fa1bd8

So, gcc emits toc sections with alignment of 8 bytes, which the linker
respects, leading to a toc pointer (r2) that can only be assumed to be 8 byte
aligned.  This completely breaks rs6000.c:offsettable_ok_by_alignment.
My bug.  Short term fix will be to limit offsettable_ok_by_alignment to 8 byte
alignment.  Longer term, modify the linker to increase r2 alignment.