https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61796
Bug ID: 61796
Summary: gcc arm hardfloat
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: other
Assignee: unassigned at gcc dot gnu.org
Reporter: luka.perkov at sartura dot hr
When building crosscompile toolchain for arm with hardware floating point
support toolchain is built with software floating point or at least that seems
to be the case. The flags passed include:
-pipe -march=armv7-a -mtune=cortex-a9 -mfpu=neon -mfloat-abi=hard
I've noticed this behaviour while building eglibc. The relevant code for this
seems to be located in the following files:
gcc/config/arm/arm.h
gcc/config/arm/arm-opts.h
gcc/gcc/config/arm/arm.opt
Regardles of the -mfloat-abi=hard flag being passed the gcc ends up setting
__SOFTFP__ which is only set if -mfloat-abi=soft is passed. Command below shows
how I tested this:
$ arm-openwrt-linux-gnueabi-gcc -x c - -E -dM </dev/null 2>/dev/null | fgrep
SOFT
#define __SOFTFP__ 1
The following hack seems to fix the problem:
--- a/gcc/config/arm/arm.opt
+++ b/gcc/config/arm/arm.opt
@@ -106,7 +106,7 @@ Target RejectNegative Joined Enum(proces
Specify the name of the target CPU
mfloat-abi=
-Target RejectNegative Joined Enum(float_abi_type) Var(arm_float_abi)
Init(TARGET_DEFAULT_FLOAT_ABI)
+Target RejectNegative Joined Enum(float_abi_type) Var(arm_float_abi)
Init(ARM_FLOAT_ABI_HARD)
Specify if floating point hardware should be used
Enum
Because of the check in eglibc (paste below) compilation fails because
__ARM_PCS_VFP is not set. The __ARM_PCS_VFP is only set if the hardware float
is used - and that should be the case, here is the relevant chunk from
gcc/config/arm/arm.c:
else if (arm_float_abi == ARM_FLOAT_ABI_HARD
&& TARGET_HARD_FLOAT
&& TARGET_VFP)
arm_pcs_default = ARM_PCS_AAPCS_VFP;
And the eglibc code refered to in the last section (libc/scripts/config.guess):
if echo __ARM_PCS_VFP | $CC_FOR_BUILD -E - 2>/dev/null \
| grep -q __ARM_PCS_VFP
then
echo ${UNAME_MACHINE}-unknown-linux-${LIBC}eabi
else
echo ${UNAME_MACHINE}-unknown-linux-${LIBC}eabihf
fi
Even though I've managed to compile eglibc successfully and entire system
without issue I didn't manage to boot it. That might be a different problem but
I'd like to hear your opinion about this bug first.
Luka
