Skip to contentSkip to conversation

package/Makefile.in: Tweak TARGET_ABI for MPC8548

PATCH New Andrey Smirnov 2 participants 5 messages Jul 12, 2017 – Jul 14, 2017

lore
Share & tools
lore

Andrey Smirnov

author
#0 lore raw

PATCH 1/1 package/Makefile.in: Tweak TARGET_ABI for MPC8548

From: Mark Hinds <[email protected]>

Add -mcpu=8548 -mhard-float to TARGET_ABI so that hardware FP is used to build all of the package in the system.

Signed-off-by Mark Hinds <[email protected]>
Signed-off-by Andrey Smirnov <[email protected]>
---
 package/Makefile.in | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
package/Makefile.in +1 -1
index b95e5e3..958d72c 100644
@@ -78,7 +78,7 @@ ifeq ($(BR2_powerpc_8540),y)
 TARGET_ABI += -mabi=spe -mfloat-gprs=single -Wa,-me500
 endif
 ifeq ($(BR2_powerpc_8548),y)
-TARGET_ABI += -mabi=spe -mfloat-gprs=double -Wa,-me500x2
+TARGET_ABI += -mabi=spe -mfloat-gprs=double -Wa,-me500x2 -mcpu=8548 -mhard-float
 endif
 ifeq ($(BR2_powerpc_e500mc),y)
 TARGET_ABI += -mabi=spe -mfloat-gprs=double -Wa,-me500mc
Signature · 1 line
2.9.4
#1 lore raw

PATCH 1/1 package/Makefile.in: Tweak TARGET_ABI for MPC8548

Hello,

Quoted 16 lines · Andrey Smirnov

From: Mark Hinds <[email protected]>

Add -mcpu=8548 -mhard-float to TARGET_ABI so that hardware FP is used to build all of the package in the system.

Signed-off-by Mark Hinds <[email protected]>
Signed-off-by Andrey Smirnov <[email protected]>
---
 package/Makefile.in | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
package/Makefile.in +0 -0
index b95e5e3..958d72c 100644

package/Makefile.in ifeq ($(BR2_powerpc_8540),y) · line 81

Quoted 5 lines
package/Makefile.in +1 -1
@@ -78,7 +78,7 @@ ifeq ($(BR2_powerpc_8540),y)
 TARGET_ABI += -mabi=spe -mfloat-gprs=single -Wa,-me500
 endif
 ifeq ($(BR2_powerpc_8548),y)
-TARGET_ABI += -mabi=spe -mfloat-gprs=double -Wa,-me500x2
+TARGET_ABI += -mabi=spe -mfloat-gprs=double -Wa,-me500x2 -mcpu=8548 -mhard-float

Adding the -mcpu is useless, because it's already passed thanks to BR2_GCC_TARGET_CPU, defined to 8548 when BR2_powerpc_8548=y in arch/Config.in.powerpc.

Unconditionally passing -mhard-float here is wrong, because people may want to use soft-float, which can be selected using the BR2_POWERPC_SOFT_FLOAT option.

When BR2_SOFT_FLOAT=y (which is selected by BR2_POWERPC_SOFT_FLOAT), we:

* Pass --with-float=soft when building gcc (see package/gcc/gcc.mk). This solves the case of internal toolchain being used.

* Add -msoft-float in the toolchain wrapper when an external toolchain is used (toolchain/toolchain-external/pkg-toolchain-external.mk).

However, we indeed never explicitly pass --with-float=hard (when building gcc) or -mhard-float (for external toolchains).

Could you describe more precisely the problem you're seeing? Are you using the internal toolchain backend, or an external toolchain? In the latter case, which external toolchain are you using?

Best regards,

Thomas

Signature · 3 lines
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
author
#2 lore raw

PATCH 1/1 package/Makefile.in: Tweak TARGET_ABI for MPC8548

Quoted 14 lines · Thomas Petazzoni

Hello,

Quoted 11 lines · Andrey Smirnov

From: Mark Hinds <[email protected]>

Add -mcpu=8548 -mhard-float to TARGET_ABI so that hardware FP is used to build all of the package in the system.

Signed-off-by Mark Hinds <[email protected]>
Signed-off-by Andrey Smirnov <[email protected]>
---
 package/Makefile.in | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
Quoted 15 lines

package/Makefile.in ifeq ($(BR2_powerpc_8540),y) · line 81

Quoted 10 lines
package/Makefile.in +1 -1
index b95e5e3..958d72c 100644
@@ -78,7 +78,7 @@ ifeq ($(BR2_powerpc_8540),y)
 TARGET_ABI += -mabi=spe -mfloat-gprs=single -Wa,-me500
 endif
 ifeq ($(BR2_powerpc_8548),y)
-TARGET_ABI += -mabi=spe -mfloat-gprs=double -Wa,-me500x2
+TARGET_ABI += -mabi=spe -mfloat-gprs=double -Wa,-me500x2 -mcpu=8548 -mhard-float

Adding the -mcpu is useless, because it's already passed thanks to BR2_GCC_TARGET_CPU, defined to 8548 when BR2_powerpc_8548=y in arch/Config.in.powerpc.

Oh! Missed that, my bad.

Quoted 4 lines

Unconditionally passing -mhard-float here is wrong, because people may want to use soft-float, which can be selected using the BR2_POWERPC_SOFT_FLOAT option.

Good point, haven't thought about that.

Quoted 8 lines

When BR2_SOFT_FLOAT=y (which is selected by BR2_POWERPC_SOFT_FLOAT), we:

* Pass --with-float=soft when building gcc (see package/gcc/gcc.mk). This solves the case of internal toolchain being used.

* Add -msoft-float in the toolchain wrapper when an external toolchain is used (toolchain/toolchain-external/pkg-toolchain-external.mk).

Quoted 7 lines

However, we indeed never explicitly pass --with-float=hard (when building gcc) or -mhard-float (for external toolchains).

Could you describe more precisely the problem you're seeing? Are you using the internal toolchain backend, or an external toolchain? In the latter case, which external toolchain are you using?

It's been a while, since I investigated this patch, but I believe we were seeing performance improvements on heavily numerical application on our system with "-mhard-float" while using custom built crosstools-ng e500 toolchain. But given how I didn't notice two significant problems with this patch and it is clearly not ready for prime time, let me go back and do more research/double check that I wasn't doing something dumb and missing the obvious.

I'll follow up with a separate patch if it's truly useful.

Thanks,
Andrey Smirnov

#3 lore raw

PATCH 1/1 package/Makefile.in: Tweak TARGET_ABI for MPC8548

Hello,

Quoted 9 lines · Andrey Smirnov

It's been a while, since I investigated this patch, but I believe we were seeing performance improvements on heavily numerical application on our system with "-mhard-float" while using custom built crosstools-ng e500 toolchain. But given how I didn't notice two significant problems with this patch and it is clearly not ready for prime time, let me go back and do more research/double check that I wasn't doing something dumb and missing the obvious.

I'll follow up with a separate patch if it's truly useful.

I think it definitely makes sense to continue work on this patch. PowerPC is not the most well maintained architecture in Buildroot, so it's very good to get contributions from our PowerPC users to improve the support for this architecture.

If indeed PowerPC needs an explicit -mhard-float to use the FPU, we'll have to fix Buildroot. Could you investigate this a little bit more?

Thanks!

Thomas

Signature · 3 lines
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
author
#4 lore raw

PATCH 1/1 package/Makefile.in: Tweak TARGET_ABI for MPC8548

Quoted 14 lines · Thomas Petazzoni

Hello,

Quoted 9 lines · Andrey Smirnov

It's been a while, since I investigated this patch, but I believe we were seeing performance improvements on heavily numerical application on our system with "-mhard-float" while using custom built crosstools-ng e500 toolchain. But given how I didn't notice two significant problems with this patch and it is clearly not ready for prime time, let me go back and do more research/double check that I wasn't doing something dumb and missing the obvious.

I'll follow up with a separate patch if it's truly useful.

Quoted 8 lines

I think it definitely makes sense to continue work on this patch. PowerPC is not the most well maintained architecture in Buildroot, so it's very good to get contributions from our PowerPC users to improve the support for this architecture.

If indeed PowerPC needs an explicit -mhard-float to use the FPU, we'll have to fix Buildroot. Could you investigate this a little bit more?

Absolutely. Sorry for not being very clear, what I was trying to say
is: I just lost a bit of confidence that this patch is truly needed(I've been confuse by simpler things before), so I'll go back and investigate more to either build a better case for it or discover what I missed.

Thanks,
Andrey Smirnov