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Date: Wed, 14 Dec 2016 11:53:06 +0100
From: Szabolcs Nagy <>
Subject: Re: musl + PowerPC + GCC 5

* A. Wilcox <> [2016-12-14 04:02:39 -0600]:
> Compiler output is:
> powerpc-foxkit-linux-musl-gcc   -g -O2 -mlong-double-64 -ggdb
> - -fno-omit-frame-pointer -pipe -O2  -g -O2 -mlong-double-64 -ggdb
> - -fno-omit-frame-pointer -pipe -DIN_GCC    -W -Wall -Wno-narrowing
> - -Wwrite-strings -Wcast-qual -Wstrict-prototypes -Wmissing-prototypes
> - -Wold-style-definition  -isystem ./include   -fPIC -mlong-double-128
> - -mno-minimal-toc -g -DIN_LIBGCC2 -fbuilding-libgcc
> - -fno-stack-protector   -fPIC -mlong-double-128 -mno-minimal-toc -I.
> - -I. -I../.././gcc
> - -I/usr/src/sys-devel/gcc-5.4.0-r2/work/gcc-5.4.0/libgcc
> - -I/usr/src/sys-devel/gcc-5.4.0-r2/work/gcc-5.4.0/libgcc/.
> - -I/usr/src/sys-devel/gcc-5.4.0-r2/work/gcc-5.4.0/libgcc/../gcc
> - -I/usr/src/sys-devel/gcc-5.4.0-r2/work/gcc-5.4.0/libgcc/../include
> - -I/usr/src/sys-devel/gcc-5.4.0-r2/work/gcc-5.4.0/libgcc/../libdecnumber/
> dpd
> - -I/usr/src/sys-devel/gcc-5.4.0-r2/work/gcc-5.4.0/libgcc/../libdecnumber
>  -o _sd_to_tf.o -MT _sd_to_tf.o -MD -MP -MF _sd_to_tf.dep
> /usr/src/sys-devel/gcc-5.4.0-r2/work/gcc-5.4.0/libgcc/dfp-bit.c
> In file included from
> /usr/src/sys-devel/gcc-5.4.0-r2/work/gcc-5.4.0/libgcc/dfp-bit.c:40:0:
> /usr/src/sys-devel/gcc-5.4.0-r2/work/gcc-5.4.0/libgcc/dfp-bit.h:288:2:
> error: #error "unknown long double size, cannot define BFP_FMT"
>  #error "unknown long double size, cannot define BFP_FMT"
>   ^
> make[2]: *** [Makefile:684: _sd_to_tf.o] Error 1

this happens when 128bit float to decimal float conversion code
is compiled: then libc sprintf with BFP_FMT is used to do the
conversion and for that libc LDBL_MANT_DIG is checked and musl
has no support for this.

i think the simplest fix is to config with --disable-decimal-float

the second simplest fix is to patch the ifdef logic (e.g. define
BFP_FMT "%Le") but then the conversion code would be broken at
runtime: the code is compiled with -mlong-double-128 and musl
expects 64 bit long double. (most likely the bootstrap process
does not depend on this to work so this is a workaround hack
that only breaks 128bit float to decimal conversion.)

the correct way on musl is to build libgcc without -mlong-double-128
and without all the 128bit (TF mode) float stuff, but this may need
some configure and build system changes as i don't immediately see
an option to turn tf mode things off.

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