[powerpc:test 7/8] include/math-emu/quad.h:72:1: error: unable to emulate 'TF'

[Joseph Myers]

On Tue, 17 Nov 2015, kbuild test robot wrote:

> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git test
> head:   e37d8480fbd6b9ad3665ac85a903098413ba67ae
> commit: 71fa67f178c6c3c338d0b99644bce808f2f0965e [7/8] sparc/math-emu: Move sparc from math-emu-old to math-emu
> config: sparc-defconfig (attached as .config)
> reproduce:
>         wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         git checkout 71fa67f178c6c3c338d0b99644bce808f2f0965e
>         # save the attached .config to linux build tree
>         make.cross ARCH=sparc 
> 
> All errors (new ones prefixed by >>):
> 
>    In file included from arch/sparc/math-emu/math_32.c:77:0:
> >> include/math-emu/quad.h:72:1: error: unable to emulate 'TF'
>     typedef float TFtype __attribute__ ((mode (TF)));

Is this with a compiler that defaults to -mlong-double-64 (which is, I 
think, now an unusual configuration on SPARC - it might arise for 
bootstrap compilers, but any normal distribution compiler should default 
to -mlong-double-128)?

If so, the old code would have been quietly building with a union that 
contains the "wrong" long double type, when using such a compiler.  And 
actually I think that because of the particular subset of macros used, 
this would have worked; the long double member of the union wouldn't have 
been used in this code.

My inclination would be to use

CFLAGS_math_32.o = -mlong-double-128
CFLAGS_math_64.o = -mlong-double-128

in arch/sparc/math-emu/Makefile to fix this properly (the "unable to 
emulate" error is for modes that fail GCC's scalar_mode_supported_p hook, 
which by default allows the modes for all standard types, hence an error 
for -mlong-double-64 when TFmode isn't used by a standard type).  Untested 
incremental patch follows.

Signed-off-by: Joseph Myers <joseph at codesourcery.com>

---

diff --git a/arch/sparc/math-emu/Makefile b/arch/sparc/math-emu/Makefile
index 825dbee..6df8769 100644
--- a/arch/sparc/math-emu/Makefile
+++ b/arch/sparc/math-emu/Makefile
@@ -5,4 +5,9 @@
 # suppress all warnings - as math.c produces a lot!
 ccflags-y := -w
 
+# Emulation of quad instructions requires -mlong-double-128 for
+# __attribute__ ((mode (TF))) to be accepted.
+CFLAGS_math_32.o = -mlong-double-128
+CFLAGS_math_64.o = -mlong-double-128
+
 obj-y    := math_$(BITS).o


-- 
Joseph S. Myers
joseph at codesourcery.com