[Buildroot] [PATCH 1/2] powerpc/spe: tweak glibc/eglibc/uclibc combinations

[Buildroot] [PATCH 1/2] powerpc/spe: tweak glibc/eglibc/uclibc combinations

[Gustavo Zacarias]

Since (e)glibc 2.19+ PowerPC SPE changed ABI conventions for sanity.
In the good old days hard-float was used, it sounds good on paper until
you account for the e500v1/v2 differences, with v1 being a fpu that does
only single-precision math.

So the ABI changed to make it soft-float and the libc (or libm) handle
that deficiency in software if required, making old precompiled binaries
incompatible (of no concern for buildroot since we've got no precompiled
binary blobs for SPE in packages).

For uClibc the support is for hard-float so disable it for soft since it
doesn't do the fallback trickery.

So do what's appropiate for each combination:

               H-F   S-F

eglibc 2.18     x
eglibc 2.19           x
glibc 2.19            x
glibc 2.20            x
uclibc          x

Eventually hard-float should just go away, i'm keeping it for
compatibility purposes.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
---
 package/glibc/Config.in                 | 4 ++--
 toolchain/toolchain-buildroot/Config.in | 3 ++-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/package/glibc/Config.in b/package/glibc/Config.in
index 8c033f2..748ff44 100644
--- a/package/glibc/Config.in
+++ b/package/glibc/Config.in
@@ -11,11 +11,11 @@ choice
 
 config BR2_EGLIBC_VERSION_2_18
 	bool "2.18-svnr23787"
+	depends on !BR2_POWERPC_SOFT_FLOAT
 
 config BR2_EGLIBC_VERSION_2_19
 	bool "2.19-svnr25243"
-	# Build breakage
-	depends on !BR2_powerpc_SPE
+	depends on !BR2_powerpc_SPE || (BR2_powerpc_SPE && BR2_POWERPC_SOFT_FLOAT)
 
 endchoice
 
diff --git a/toolchain/toolchain-buildroot/Config.in b/toolchain/toolchain-buildroot/Config.in
index 53d86dd..9a711c0 100644
--- a/toolchain/toolchain-buildroot/Config.in
+++ b/toolchain/toolchain-buildroot/Config.in
@@ -33,6 +33,7 @@ config BR2_TOOLCHAIN_BUILDROOT_UCLIBC
 		   BR2_mips    || BR2_mipsel || BR2_mips64 || BR2_mips64el || \
 		   BR2_powerpc || BR2_sh     || BR2_sparc  || BR2_xtensa   || \
 		   BR2_x86_64
+	depends on !BR2_powerpc_SPE || (BR2_powerpc_SPE && !BR2_POWERPC_SOFT_FLOAT)
 	help
 	  This option selects uClibc as the C library for the
 	  cross-compilation toolchain.
@@ -67,7 +68,7 @@ config BR2_TOOLCHAIN_BUILDROOT_GLIBC
 		   BR2_microblaze
 	depends on BR2_USE_MMU
 	depends on !BR2_PREFER_STATIC_LIB
-	depends on !BR2_powerpc_SPE
+	depends on !BR2_powerpc_SPE || (BR2_powerpc_SPE && BR2_POWERPC_SOFT_FLOAT)
 	select BR2_TOOLCHAIN_USES_GLIBC
 	# our glibc.mk enables RPC support
 	select BR2_TOOLCHAIN_HAS_NATIVE_RPC
-- 
1.8.5.5

[Buildroot] [PATCH 2/2] arch/powerpc: default to soft-float for SPE ABI

[Gustavo Zacarias]

It really is the way forward so switch the default.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
---
 arch/Config.in.powerpc | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/Config.in.powerpc b/arch/Config.in.powerpc
index 239f5dc..4c21739 100644
--- a/arch/Config.in.powerpc
+++ b/arch/Config.in.powerpc
@@ -141,6 +141,7 @@ endchoice
 
 config BR2_POWERPC_SOFT_FLOAT
 	bool "Use soft-float"
+	default y if BR2_powerpc_SPE
 	select BR2_SOFT_FLOAT
 	help
 	  If your target CPU does not have a Floating Point Unit (FPU)
-- 
1.8.5.5

[Buildroot] [PATCH 1/2] powerpc/spe: tweak glibc/eglibc/uclibc combinations

[Thomas Petazzoni]

Dear Gustavo Zacarias,

On Thu, 11 Sep 2014 08:56:31 -0300, Gustavo Zacarias wrote:
> Since (e)glibc 2.19+ PowerPC SPE changed ABI conventions for sanity.
> In the good old days hard-float was used, it sounds good on paper until
> you account for the e500v1/v2 differences, with v1 being a fpu that does
> only single-precision math.
> 
> So the ABI changed to make it soft-float and the libc (or libm) handle
> that deficiency in software if required, making old precompiled binaries
> incompatible (of no concern for buildroot since we've got no precompiled
> binary blobs for SPE in packages).

I'm not sure to fully understand: is PowerPC really using *soft-float*
as in all floating point operations are emulated in software? Or is it
a difference similar to the difference between hardfp and softfp on ARM
(both use the FPU and floating point instructions, it's only a
different ABI, where hardfp passes floating point arguments in floating
point registers, while softfp passes floating point arguments in
integer registers).

Thanks,

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

[Buildroot] [PATCH 1/2] powerpc/spe: tweak glibc/eglibc/uclibc combinations

[Gustavo Zacarias]

On 09/11/2014 05:57 PM, Thomas Petazzoni wrote:

> I'm not sure to fully understand: is PowerPC really using *soft-float*
> as in all floating point operations are emulated in software? Or is it
> a difference similar to the difference between hardfp and softfp on ARM
> (both use the FPU and floating point instructions, it's only a
> different ABI, where hardfp passes floating point arguments in floating
> point registers, while softfp passes floating point arguments in
> integer registers).

It's similar to the ARM scenario, yes.
In the SPE ABI there are no FPU registers at all, it's just an extension
of GP-ones (say 32+32 bit for DP/E500v2).
In libc-land uclibc uses the 'old' ABI (direct hard float), and so did
eglibc <= 2.18 (glibc i think never got that part officially).
To avoid re-explaining: http://www.eglibc.org/archives/patches/msg01291.html
I hope it's clear enough :)
Regards.