Re: RFA: correct size of long double on PPC Linux

[Jim Blandy <jimb@redhat.com>]

Kevin Buettner <kevinb@redhat.com> writes:

> On 26 Mar 2004 10:45:13 -0500
> Jim Blandy <jimb@redhat.com> wrote:
> 
> > Daniel Jacobowitz <drow@false.org> writes:
> > 
> > > On Thu, Mar 25, 2004 at 10:23:58PM -0700, Kevin Buettner wrote:
> > > > On 24 Mar 2004 13:10:33 -0500
> > > > Jim Blandy <jimb@redhat.com> wrote:
> > > > 
> > > > > 2004-03-24  Jim Blandy  <jimb@redhat.com>
> > > > > 
> > > > > 	* ppc-linux-tdep.c (ppc_linux_init_abi): Long doubles are eight
> > > > > 	bytes long on PPC Linux.
> > > > 
> > > > Can you provide the ABI reference for this?
> > > > 
> > > > According to the documentation that I have (which is the System V ABI
> > > > PowerPC Processor Supplement), the size of a long double is 16 bytes.
> > > 
> > > Yes - this is one of the known warts in the PPC GNU/Linux ABI.  People
> > > have been talking for years about fixing it to match the SysV ABI.  GCC
> > > only recently got 128-bit long double support on PPC, so it may be
> > > changing soon; but for all existing PPC GNU/Linux systems I know of,
> > > eight bytes is correct.
> > 
> > I went to the Linux Standards Base, and it said that programs that use
> > 'long double' on PPC Linux are non-conformant.  So I figured the best
> > I could do was to make GDB match GCC.
> 
> Okay, this patch is approved then, so long as you add a suitable comment
> about PPC Linux deviating from the System V ABI on this matter.

Okay, thanks.  I've committed the following:

2004-03-24  Jim Blandy  <jimb@redhat.com>

	* ppc-linux-tdep.c (ppc_linux_init_abi): Long doubles are eight
	bytes long on PPC Linux.

Index: ppc-linux-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/ppc-linux-tdep.c,v
retrieving revision 1.54
retrieving revision 1.55
diff -c -c -F'^(' -r1.54 -r1.55
*** ppc-linux-tdep.c	23 Mar 2004 14:47:56 -0000	1.54
--- ppc-linux-tdep.c	26 Mar 2004 20:59:38 -0000	1.55
***************
*** 1076,1081 ****
--- 1076,1090 ----
  
    if (tdep->wordsize == 4)
      {
+       /* NOTE: jimb/2004-03-26: The System V ABI PowerPC Processor
+          Supplement says that long doubles are sixteen bytes long.
+          However, as one of the known warts of its ABI, PPC GNU/Linux
+          uses eight-byte long doubles.  GCC only recently got 128-bit
+          long double support on PPC, so it may be changing soon.  The
+          Linux Standards Base says that programs that use 'long
+          double' on PPC GNU/Linux are non-conformant.  */
+       set_gdbarch_long_double_bit (gdbarch, 8 * TARGET_CHAR_BIT);
+ 
        /* Until November 2001, gcc did not comply with the 32 bit SysV
  	 R4 ABI requirement that structures less than or equal to 8
  	 bytes should be returned in registers.  Instead GCC was using