[Buildroot] [PATCH 1/1] [1/1] package/uclibc: Enable compile in thumb mode when selected

[Buildroot] [PATCH 1/1] [1/1] package/uclibc: Enable compile in thumb mode when selected

[penman]

Signed-off-by: penman <paul.enman@gmail.com>
---
 package/uclibc/uclibc.mk | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/package/uclibc/uclibc.mk b/package/uclibc/uclibc.mk
index c62a40f..4f5c605 100644
--- a/package/uclibc/uclibc.mk
+++ b/package/uclibc/uclibc.mk
@@ -86,9 +86,15 @@ define UCLIBC_ARM_ABI_CONFIG
 	$(call KCONFIG_ENABLE_OPT,CONFIG_ARM_EABI,$(@D)/.config)
 endef
 
-# Thumb build is broken with threads, build in ARM mode
-ifeq ($(BR2_ARM_INSTRUCTIONS_THUMB)$(BR2_TOOLCHAIN_HAS_THREADS),yy)
-UCLIBC_EXTRA_CFLAGS += -marm
+ifeq ($(BR2_ARM_INSTRUCTIONS_THUMB)$(BR2_ARM_INSTRUCTIONS_THUMB2),y)
+define UCLIBC_ARM_THUMB_CONFIG
+	$(call KCONFIG_ENABLE_OPT,COMPILE_IN_THUMB_MODE,$(@D)/.config)
+	$(call KCONFIG_DISABLE_OPT,UCLIBC_HAS_CONTEXT_FUNCS,$(@D)/.config)
+endef
+else
+define UCLIBC_ARM_THUMB_CONFIG
+	$(call KCONFIG_DISABLE_OPT,COMPILE_IN_THUMB_MODE,$(@D)/.config)
+endef
 endif
 
 ifeq ($(BR2_UCLIBC_ARM_BX),y)
@@ -373,6 +379,7 @@ define UCLIBC_KCONFIG_FIXUP_CMDS
 	$(UCLIBC_ARC_TYPE_CONFIG)
 	$(UCLIBC_ARC_PAGE_SIZE_CONFIG)
 	$(UCLIBC_ARM_ABI_CONFIG)
+	$(UCLIBC_ARM_THUMB_CONFIG)
 	$(UCLIBC_ARM_BX_CONFIG)
 	$(UCLIBC_MIPS_ABI_CONFIG)
 	$(UCLIBC_MIPS_ISA_CONFIG)
-- 
1.9.1

[Buildroot] [PATCH 1/1] [1/1] package/uclibc: Enable compile in thumb mode when selected

[Arnout Vandecappelle]

 Hi penman,

On 04-12-15 23:56, penman wrote:
> Signed-off-by: penman <paul.enman@gmail.com>

 Please use your full real name in the Sob (I guess that's Paul Enman).

> ---
>  package/uclibc/uclibc.mk | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/package/uclibc/uclibc.mk b/package/uclibc/uclibc.mk
> index c62a40f..4f5c605 100644
> --- a/package/uclibc/uclibc.mk
> +++ b/package/uclibc/uclibc.mk
> @@ -86,9 +86,15 @@ define UCLIBC_ARM_ABI_CONFIG
>  	$(call KCONFIG_ENABLE_OPT,CONFIG_ARM_EABI,$(@D)/.config)
>  endef
>  
> -# Thumb build is broken with threads, build in ARM mode

 Can you explain what changed in the last two years since this fix was
introduced in commit d244782ca? It might have been fixed in -ng, but 0.9.33.2
hasn't changed in a very long time so I guess it's still broken there. You'll
need to add a condition on -NG.

 Or it could be gcc that has been fixed, but in that case please verify that it
works with gcc-4.7

 Regards,
 Arnout

> -ifeq ($(BR2_ARM_INSTRUCTIONS_THUMB)$(BR2_TOOLCHAIN_HAS_THREADS),yy)
> -UCLIBC_EXTRA_CFLAGS += -marm
> +ifeq ($(BR2_ARM_INSTRUCTIONS_THUMB)$(BR2_ARM_INSTRUCTIONS_THUMB2),y)
> +define UCLIBC_ARM_THUMB_CONFIG
> +	$(call KCONFIG_ENABLE_OPT,COMPILE_IN_THUMB_MODE,$(@D)/.config)
> +	$(call KCONFIG_DISABLE_OPT,UCLIBC_HAS_CONTEXT_FUNCS,$(@D)/.config)
> +endef
> +else
> +define UCLIBC_ARM_THUMB_CONFIG
> +	$(call KCONFIG_DISABLE_OPT,COMPILE_IN_THUMB_MODE,$(@D)/.config)
> +endef
>  endif
>  
>  ifeq ($(BR2_UCLIBC_ARM_BX),y)
> @@ -373,6 +379,7 @@ define UCLIBC_KCONFIG_FIXUP_CMDS
>  	$(UCLIBC_ARC_TYPE_CONFIG)
>  	$(UCLIBC_ARC_PAGE_SIZE_CONFIG)
>  	$(UCLIBC_ARM_ABI_CONFIG)
> +	$(UCLIBC_ARM_THUMB_CONFIG)
>  	$(UCLIBC_ARM_BX_CONFIG)
>  	$(UCLIBC_MIPS_ABI_CONFIG)
>  	$(UCLIBC_MIPS_ISA_CONFIG)
> 


-- 
Arnout Vandecappelle                          arnout at mind be
Senior Embedded Software Architect            +32-16-286500
Essensium/Mind                                http://www.mind.be
G.Geenslaan 9, 3001 Leuven, Belgium           BE 872 984 063 RPR Leuven
LinkedIn profile: http://www.linkedin.com/in/arnoutvandecappelle
GPG fingerprint:  7493 020B C7E3 8618 8DEC 222C 82EB F404 F9AC 0DDF

[Buildroot] [PATCH 1/1] [1/1] package/uclibc: Enable compile in thumb mode when selected

[Paul Enman]

Hi Arnout,
Thanks, I checked the old commit and tested with both uClibc-0.9.33 and
uClibc-ng and older gcc; I was suprised to discover updated gcc versions
resolve the issue (uclibc/arm: doesn't build in thumb(1) mode with threads).

With this existing (v1) patch, for example:
Config: arm926t, thumb1; builds only with gcc-4.9 or better
Config: cortex-a5, thumb2; builds with all configuration options gcc-4.7
through gcc-5.x
Config: cortex-m3, thumb1 or thumb2; builds with all configuration options
gcc-4.7 though gcc-5.x

Since uclibc has some unresolved cases building with older gcc using
thumb1, I'll limit the scope and prepare a v2 patch that will pass the
thumb config option to uclibc when using thumb2 instruction set and not
interfere with the existing thumb1 workaround that relies on interworking
between arm and thumb instructions.

On Sat, Dec 5, 2015 at 9:08 AM, Arnout Vandecappelle <arnout@mind.be> wrote:

>  Hi penman,
>
> On 04-12-15 23:56, penman wrote:
> > Signed-off-by: penman <paul.enman@gmail.com>
>
>  Please use your full real name in the Sob (I guess that's Paul Enman).
>
> > ---
> >  package/uclibc/uclibc.mk | 13 ++++++++++---
> >  1 file changed, 10 insertions(+), 3 deletions(-)
> >
> > diff --git a/package/uclibc/uclibc.mk b/package/uclibc/uclibc.mk
> > index c62a40f..4f5c605 100644
> > --- a/package/uclibc/uclibc.mk
> > +++ b/package/uclibc/uclibc.mk
> > @@ -86,9 +86,15 @@ define UCLIBC_ARM_ABI_CONFIG
> >       $(call KCONFIG_ENABLE_OPT,CONFIG_ARM_EABI,$(@D)/.config)
> >  endef
> >
> > -# Thumb build is broken with threads, build in ARM mode
>
>  Can you explain what changed in the last two years since this fix was
> introduced in commit d244782ca? It might have been fixed in -ng, but
> 0.9.33.2
> hasn't changed in a very long time so I guess it's still broken there.
> You'll
> need to add a condition on -NG.
>
>  Or it could be gcc that has been fixed, but in that case please verify
> that it
> works with gcc-4.7
>
>  Regards,
>  Arnout
>
> > -ifeq ($(BR2_ARM_INSTRUCTIONS_THUMB)$(BR2_TOOLCHAIN_HAS_THREADS),yy)
> > -UCLIBC_EXTRA_CFLAGS += -marm
> > +ifeq ($(BR2_ARM_INSTRUCTIONS_THUMB)$(BR2_ARM_INSTRUCTIONS_THUMB2),y)
> > +define UCLIBC_ARM_THUMB_CONFIG
> > +     $(call KCONFIG_ENABLE_OPT,COMPILE_IN_THUMB_MODE,$(@D)/.config)
> > +     $(call KCONFIG_DISABLE_OPT,UCLIBC_HAS_CONTEXT_FUNCS,$(@D)/.config)
> > +endef
> > +else
> > +define UCLIBC_ARM_THUMB_CONFIG
> > +     $(call KCONFIG_DISABLE_OPT,COMPILE_IN_THUMB_MODE,$(@D)/.config)
> > +endef
> >  endif
> >
> >  ifeq ($(BR2_UCLIBC_ARM_BX),y)
> > @@ -373,6 +379,7 @@ define UCLIBC_KCONFIG_FIXUP_CMDS
> >       $(UCLIBC_ARC_TYPE_CONFIG)
> >       $(UCLIBC_ARC_PAGE_SIZE_CONFIG)
> >       $(UCLIBC_ARM_ABI_CONFIG)
> > +     $(UCLIBC_ARM_THUMB_CONFIG)
> >       $(UCLIBC_ARM_BX_CONFIG)
> >       $(UCLIBC_MIPS_ABI_CONFIG)
> >       $(UCLIBC_MIPS_ISA_CONFIG)
> >
>
>
> --
> Arnout Vandecappelle                          arnout at mind be
> Senior Embedded Software Architect            +32-16-286500
> Essensium/Mind                                http://www.mind.be
> G.Geenslaan 9, 3001 Leuven, Belgium           BE 872 984 063 RPR Leuven
> LinkedIn profile: http://www.linkedin.com/in/arnoutvandecappelle
> GPG fingerprint:  7493 020B C7E3 8618 8DEC 222C 82EB F404 F9AC 0DDF
>
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[Buildroot] [PATCH v2] package/uclibc: Enable compile in thumb mode configuration option

[Paul Enman]

From: penman <paul.enman@gmail.com>

Signed-off-by: Paul Enman <paul.enman@gmail.com>
---

When buildroot is configured to build uClibc with thumb, it uses a workaround
 for that relies on interworking between arm and thumb instructions and does
 not set the config file to enable compile in thumb mode.

This patch enables buildroot to configure and compile uClibc in thumb mode.

 arch/Config.in.arm       | 18 +++++++++---------
 package/uclibc/uclibc.mk | 12 ++++++++++++
 2 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/arch/Config.in.arm b/arch/Config.in.arm
index 67ff384..2d318f2 100644
--- a/arch/Config.in.arm
+++ b/arch/Config.in.arm
@@ -374,6 +374,15 @@ config BR2_ARM_INSTRUCTIONS_ARM
 	  This option instructs the compiler to generate regular ARM
 	  instructions, that are all 32 bits wide.
 
+config BR2_ARM_INSTRUCTIONS_THUMB2
+	bool "Thumb2"
+	depends on BR2_ARM_CPU_HAS_THUMB2
+	help
+	  This option instructions the compiler to generate Thumb2
+	  instructions, which allows to mix 16 bits instructions and
+	  32 bits instructions. This generally provides a much smaller
+	  compiled binary size.
+
 config BR2_ARM_INSTRUCTIONS_THUMB
 	bool "Thumb"
 	depends on BR2_ARM_CPU_HAS_THUMB
@@ -389,15 +398,6 @@ comment "Thumb1 is not compatible with VFP"
 	depends on BR2_ARM_CPU_HAS_THUMB
 	depends on !BR2_ARM_SOFT_FLOAT
 
-config BR2_ARM_INSTRUCTIONS_THUMB2
-	bool "Thumb2"
-	depends on BR2_ARM_CPU_HAS_THUMB2
-	help
-	  This option instructions the compiler to generate Thumb2
-	  instructions, which allows to mix 16 bits instructions and
-	  32 bits instructions. This generally provides a much smaller
-	  compiled binary size.
-
 endchoice
 
 config BR2_ARCH
diff --git a/package/uclibc/uclibc.mk b/package/uclibc/uclibc.mk
index c62a40f..6685325 100644
--- a/package/uclibc/uclibc.mk
+++ b/package/uclibc/uclibc.mk
@@ -91,6 +91,17 @@ ifeq ($(BR2_ARM_INSTRUCTIONS_THUMB)$(BR2_TOOLCHAIN_HAS_THREADS),yy)
 UCLIBC_EXTRA_CFLAGS += -marm
 endif
 
+ifeq ($(BR2_ARM_INSTRUCTIONS_THUMB2),y)
+define UCLIBC_ARM_THUMB_CONFIG
+	$(call KCONFIG_ENABLE_OPT,COMPILE_IN_THUMB_MODE,$(@D)/.config)
+	$(call KCONFIG_DISABLE_OPT,UCLIBC_HAS_CONTEXT_FUNCS,$(@D)/.config)
+endef
+else
+define UCLIBC_ARM_THUMB_CONFIG
+	$(call KCONFIG_DISABLE_OPT,COMPILE_IN_THUMB_MODE,$(@D)/.config)
+endef
+endif
+
 ifeq ($(BR2_UCLIBC_ARM_BX),y)
 define UCLIBC_ARM_BX_CONFIG
 	$(call KCONFIG_ENABLE_OPT,USE_BX,$(@D)/.config)
@@ -373,6 +384,7 @@ define UCLIBC_KCONFIG_FIXUP_CMDS
 	$(UCLIBC_ARC_TYPE_CONFIG)
 	$(UCLIBC_ARC_PAGE_SIZE_CONFIG)
 	$(UCLIBC_ARM_ABI_CONFIG)
+	$(UCLIBC_ARM_THUMB_CONFIG)
 	$(UCLIBC_ARM_BX_CONFIG)
 	$(UCLIBC_MIPS_ABI_CONFIG)
 	$(UCLIBC_MIPS_ISA_CONFIG)
-- 
1.9.1

[Buildroot] [PATCH v2] package/uclibc: Enable compile in thumb mode configuration option

[Thomas Petazzoni]

Paul,

On Sun, 13 Dec 2015 19:28:40 -0600, Paul Enman wrote:
> From: penman <paul.enman@gmail.com>

This is still not good, it should be your full name here as well.

> 
> Signed-off-by: Paul Enman <paul.enman@gmail.com>
> ---
> 
> When buildroot is configured to build uClibc with thumb, it uses a workaround
>  for that relies on interworking between arm and thumb instructions and does
>  not set the config file to enable compile in thumb mode.
> 
> This patch enables buildroot to configure and compile uClibc in thumb mode.

Why do you put all these explanations after the "---" sign? They should
really be part of the commit log.

> 
>  arch/Config.in.arm       | 18 +++++++++---------
>  package/uclibc/uclibc.mk | 12 ++++++++++++
>  2 files changed, 21 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/Config.in.arm b/arch/Config.in.arm
> index 67ff384..2d318f2 100644
> --- a/arch/Config.in.arm
> +++ b/arch/Config.in.arm
> @@ -374,6 +374,15 @@ config BR2_ARM_INSTRUCTIONS_ARM
>  	  This option instructs the compiler to generate regular ARM
>  	  instructions, that are all 32 bits wide.
>  
> +config BR2_ARM_INSTRUCTIONS_THUMB2
> +	bool "Thumb2"
> +	depends on BR2_ARM_CPU_HAS_THUMB2
> +	help
> +	  This option instructions the compiler to generate Thumb2
> +	  instructions, which allows to mix 16 bits instructions and
> +	  32 bits instructions. This generally provides a much smaller
> +	  compiled binary size.
> +
>  config BR2_ARM_INSTRUCTIONS_THUMB
>  	bool "Thumb"
>  	depends on BR2_ARM_CPU_HAS_THUMB
> @@ -389,15 +398,6 @@ comment "Thumb1 is not compatible with VFP"
>  	depends on BR2_ARM_CPU_HAS_THUMB
>  	depends on !BR2_ARM_SOFT_FLOAT
>  
> -config BR2_ARM_INSTRUCTIONS_THUMB2
> -	bool "Thumb2"
> -	depends on BR2_ARM_CPU_HAS_THUMB2
> -	help
> -	  This option instructions the compiler to generate Thumb2
> -	  instructions, which allows to mix 16 bits instructions and
> -	  32 bits instructions. This generally provides a much smaller
> -	  compiled binary size.

I don't understand why you are re-ordering the options here. Why are
you doing this?

> +ifeq ($(BR2_ARM_INSTRUCTIONS_THUMB2),y)
> +define UCLIBC_ARM_THUMB_CONFIG
> +	$(call KCONFIG_ENABLE_OPT,COMPILE_IN_THUMB_MODE,$(@D)/.config)

According to the help text of this uClibc option:

          Say 'y' here to force building uClibc in thumb mode.
          Say 'n' to use your compiler's default mode.

When you have BR2_ARM_INSTRUCTIONS_THUMB2, the compiler already
produces Thumb2 code by default, because the compiler is built with
--with-mode=thumb.

So could you be more specific on which cases this patch is fixing by
expanding the commit log?

> +	$(call KCONFIG_DISABLE_OPT,UCLIBC_HAS_CONTEXT_FUNCS,$(@D)/.config)

What is the relation between this and Thumb ?

Also, note that there is already some Thumb-related stuff in uclibc.mk,
which precisely forces to *not* use Thumb (1):

# Thumb build is broken with threads, build in ARM mode
ifeq ($(BR2_ARM_INSTRUCTIONS_THUMB)$(BR2_TOOLCHAIN_HAS_THREADS),yy)
UCLIBC_EXTRA_CFLAGS += -marm
endif

Thanks,

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

[Buildroot] [PATCH v2] package/uclibc: Enable compile in thumb mode configuration option

[Waldemar Brodkorb]

Hi,
Thomas Petazzoni wrote,
> Paul,
> 
> > +	$(call KCONFIG_DISABLE_OPT,UCLIBC_HAS_CONTEXT_FUNCS,$(@D)/.config)
> 
> What is the relation between this and Thumb ?

The user context manipulation functions in uClibc are using
non-thumb instructions and result in a compile failure.
 
> Also, note that there is already some Thumb-related stuff in uclibc.mk,
> which precisely forces to *not* use Thumb (1):
> 
> # Thumb build is broken with threads, build in ARM mode
> ifeq ($(BR2_ARM_INSTRUCTIONS_THUMB)$(BR2_TOOLCHAIN_HAS_THREADS),yy)
> UCLIBC_EXTRA_CFLAGS += -marm
> endif

This is no longer the case for uClibc-ng. There where fixes made,
even in uClibc master to allow building thumb-only builds with
threads enabled.

I can just not recall, if Linuxthreads or NPTL must be used for
that, or if both are working. May be Paul can check it? 
Paul, do you have a embedded system, where you test this?
Is it a noMMU cortex-m3/cortex-m4 or some MMU system?

best regards
 Waldemar

[Buildroot] [PATCH v2] package/uclibc: Enable compile in thumb mode configuration option

[Arnout Vandecappelle]

On 16-12-15 08:10, Waldemar Brodkorb wrote:
> Hi,
> Thomas Petazzoni wrote,
>> Paul,
>>
>>> +	$(call KCONFIG_DISABLE_OPT,UCLIBC_HAS_CONTEXT_FUNCS,$(@D)/.config)
>>
>> What is the relation between this and Thumb ?
> 
> The user context manipulation functions in uClibc are using
> non-thumb instructions and result in a compile failure.

 Some packages need context functions, that's why they are enabled in our
default uClibc config. Cfr. d01aaa7 (by you, Waldemar).

 So if you do this, you'll need to make some packages depend on !THUMB. While
they actually did work before this commit.

 Can't uClibc be fixed to enable interworking for the context functions so they
will work even if the rest of the library is compiled in thumb mode?


>> Also, note that there is already some Thumb-related stuff in uclibc.mk,
>> which precisely forces to *not* use Thumb (1):

 But this patch is only concerned with thumb2, not thumb1. This patch will
actually explicitly disable the COMPILE_IN_THUMB uClibc option for thumb1 (which
is usually no difference with the current situation, since it is not enabled in
the default config). So this looks OK to me.

>>
>> # Thumb build is broken with threads, build in ARM mode
>> ifeq ($(BR2_ARM_INSTRUCTIONS_THUMB)$(BR2_TOOLCHAIN_HAS_THREADS),yy)
>> UCLIBC_EXTRA_CFLAGS += -marm
>> endif
> 
> This is no longer the case for uClibc-ng. There where fixes made,
> even in uClibc master to allow building thumb-only builds with
> threads enabled.

 As I commented in v1 of this patch, as long as 0.9.33 is not killed, we can't
do this. We could however add a condition on -ng.


 Regards,
 Arnout

> I can just not recall, if Linuxthreads or NPTL must be used for
> that, or if both are working. May be Paul can check it? 
> Paul, do you have a embedded system, where you test this?
> Is it a noMMU cortex-m3/cortex-m4 or some MMU system?
> 
> best regards
>  Waldemar
> _______________________________________________
> buildroot mailing list
> buildroot at busybox.net
> http://lists.busybox.net/mailman/listinfo/buildroot
> 


-- 
Arnout Vandecappelle                          arnout at mind be
Senior Embedded Software Architect            +32-16-286500
Essensium/Mind                                http://www.mind.be
G.Geenslaan 9, 3001 Leuven, Belgium           BE 872 984 063 RPR Leuven
LinkedIn profile: http://www.linkedin.com/in/arnoutvandecappelle
GPG fingerprint:  7493 020B C7E3 8618 8DEC 222C 82EB F404 F9AC 0DDF

[Buildroot] [PATCH v2] package/uclibc: Enable compile in thumb mode configuration option

[Arnout Vandecappelle]

On 15-12-15 23:03, Thomas Petazzoni wrote:
> Paul,
> 
> On Sun, 13 Dec 2015 19:28:40 -0600, Paul Enman wrote:
[snip]
>> +ifeq ($(BR2_ARM_INSTRUCTIONS_THUMB2),y)
>> +define UCLIBC_ARM_THUMB_CONFIG
>> +	$(call KCONFIG_ENABLE_OPT,COMPILE_IN_THUMB_MODE,$(@D)/.config)
> 
> According to the help text of this uClibc option:
> 
>           Say 'y' here to force building uClibc in thumb mode.
>           Say 'n' to use your compiler's default mode.
> 
> When you have BR2_ARM_INSTRUCTIONS_THUMB2, the compiler already
> produces Thumb2 code by default, because the compiler is built with
> --with-mode=thumb.

 And in fact, the only thing that this option does is add -mthumb to CFLAGS,
which is indeed quite useless for our internal compiler.

 Or actually, it's not, because it also selects USE_BX and USE_LDREXSTREX.
USE_BX is currently handled by BR2_UCLIBC_ARM_BX but this is a cleaner way I
think. USE_LDREXSTREX is a better alternative to the SWP instruction so that's
interesting as well.

 Hm, looking at the uClibc code, there's something I don't quite understand.
USE_LDREXSTREX is selected by COMPILE_IN_THUMB_MODE, but in fact ldrex/strex are
only available on ARMv6+, so won't this break down on ARMv5?


 Regards,
 Arnout


> 
> So could you be more specific on which cases this patch is fixing by
> expanding the commit log?

[snip]



-- 
Arnout Vandecappelle                          arnout at mind be
Senior Embedded Software Architect            +32-16-286500
Essensium/Mind                                http://www.mind.be
G.Geenslaan 9, 3001 Leuven, Belgium           BE 872 984 063 RPR Leuven
LinkedIn profile: http://www.linkedin.com/in/arnoutvandecappelle
GPG fingerprint:  7493 020B C7E3 8618 8DEC 222C 82EB F404 F9AC 0DDF

[Buildroot] [PATCH v2] package/uclibc: Enable compile in thumb mode configuration option

[Paul Enman]

Hi All,
Thanks for your feedback and insight. Buildroot does build a working
Cortex-M (thumb instructions only) uClibc toolchain by touching up the
uClibc(-ng) config file with

Enable COMPILE_IN_THUMB_MODE
and
Disable UCLIBC_HAS_CONTEXT_FUNCS

ARMv5 and thumb1 targets shouldn't be effected by this patch; I'll look
into guarding packages that depend on (obsolescent?) context control
functions and prepare an updated version for review.

The toolchain compiles a bootable kernel and both Linuxthreads and NPTL
build without error, however I am looking into why flthdr shows busybox
bFLT flags are set to 0x2 (Has-PIC-GOT).

On Wed, Dec 16, 2015 at 4:08 PM, Arnout Vandecappelle <arnout@mind.be>
wrote:

> On 15-12-15 23:03, Thomas Petazzoni wrote:
> > Paul,
> >
> > On Sun, 13 Dec 2015 19:28:40 -0600, Paul Enman wrote:
> [snip]
> >> +ifeq ($(BR2_ARM_INSTRUCTIONS_THUMB2),y)
> >> +define UCLIBC_ARM_THUMB_CONFIG
> >> +    $(call KCONFIG_ENABLE_OPT,COMPILE_IN_THUMB_MODE,$(@D)/.config)
> >
> > According to the help text of this uClibc option:
> >
> >           Say 'y' here to force building uClibc in thumb mode.
> >           Say 'n' to use your compiler's default mode.
> >
> > When you have BR2_ARM_INSTRUCTIONS_THUMB2, the compiler already
> > produces Thumb2 code by default, because the compiler is built with
> > --with-mode=thumb.
>
>  And in fact, the only thing that this option does is add -mthumb to
> CFLAGS,
> which is indeed quite useless for our internal compiler.
>
>  Or actually, it's not, because it also selects USE_BX and USE_LDREXSTREX.
> USE_BX is currently handled by BR2_UCLIBC_ARM_BX but this is a cleaner way
> I
> think. USE_LDREXSTREX is a better alternative to the SWP instruction so
> that's
> interesting as well.
>
>  Hm, looking at the uClibc code, there's something I don't quite
> understand.
> USE_LDREXSTREX is selected by COMPILE_IN_THUMB_MODE, but in fact
> ldrex/strex are
> only available on ARMv6+, so won't this break down on ARMv5?
>
>
>  Regards,
>  Arnout
>
>
> >
> > So could you be more specific on which cases this patch is fixing by
> > expanding the commit log?
>
> [snip]
>
>
>
> --
> Arnout Vandecappelle                          arnout at mind be
> Senior Embedded Software Architect            +32-16-286500
> Essensium/Mind                                http://www.mind.be
> G.Geenslaan 9, 3001 Leuven, Belgium           BE 872 984 063 RPR Leuven
> LinkedIn profile: http://www.linkedin.com/in/arnoutvandecappelle
> GPG fingerprint:  7493 020B C7E3 8618 8DEC 222C 82EB F404 F9AC 0DDF
>
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[Buildroot] [PATCH v2] package/uclibc: Enable compile in thumb mode configuration option

[Arnout Vandecappelle]

 Hi Paul,

 [Please don't top-post, but reply inline like I do below.]

On 18-12-15 01:11, Paul Enman wrote:
> Hi All,
> Thanks for your feedback and insight. Buildroot does build a working Cortex-M
> (thumb instructions only) uClibc toolchain by touching up the uClibc(-ng) config
> file with
> 
> Enable COMPILE_IN_THUMB_MODE
> and
> Disable UCLIBC_HAS_CONTEXT_FUNCS
> 
> ARMv5 and thumb1 targets shouldn't be effected by this patch; I'll look into
> guarding packages that depend on (obsolescent?) context control functions and
> prepare an updated version for review.

 It will be quite hard to find such packages - especially longer term. There
probably should be a thumb2 toolchain added to the autobuilders to cover this case.

 Also, finding a good explanation for the comment is going to be difficult...
Something like "foo needs ARM instructions or a (e)glibc or musl toolchain".


 Regards,
 Arnout


> The toolchain compiles a bootable kernel and both Linuxthreads and NPTL build
> without error, however I am looking into why flthdr shows busybox bFLT flags are
> set to 0x2 (Has-PIC-GOT).

[snip]


-- 
Arnout Vandecappelle                          arnout at mind be
Senior Embedded Software Architect            +32-16-286500
Essensium/Mind                                http://www.mind.be
G.Geenslaan 9, 3001 Leuven, Belgium           BE 872 984 063 RPR Leuven
LinkedIn profile: http://www.linkedin.com/in/arnoutvandecappelle
GPG fingerprint:  7493 020B C7E3 8618 8DEC 222C 82EB F404 F9AC 0DDF

[Buildroot] [PATCH v2] package/uclibc: Enable compile in thumb mode configuration option

[Waldemar Brodkorb]

Hi Arnout,
Arnout Vandecappelle wrote,

> On 16-12-15 08:10, Waldemar Brodkorb wrote:
> > Hi,
> > Thomas Petazzoni wrote,
> >> Paul,
> >>
> >>> +	$(call KCONFIG_DISABLE_OPT,UCLIBC_HAS_CONTEXT_FUNCS,$(@D)/.config)
> >>
> >> What is the relation between this and Thumb ?
> > 
> > The user context manipulation functions in uClibc are using
> > non-thumb instructions and result in a compile failure.
> 
>  Some packages need context functions, that's why they are enabled in our
> default uClibc config. Cfr. d01aaa7 (by you, Waldemar).

Yeah. But the context functions are deprecated and POSIX suggests
not to use them. Unfortunately they are only implemented for
arm/mips/x86/x86_64 in uClibc. Someone could port the implementation
for other architectures from GNU libc. But then still all noMMU
architectures would be missing. Furthermore the GNU libc
implementation does not work for THUMB only builds.
 
>  So if you do this, you'll need to make some packages depend on !THUMB. While
> they actually did work before this commit.

They did work before for people trying to run thumb code on a ARM
core which allows both modes. (arm and thumb)
But without this patch people can not use it to do a thumb2-only
build, which is a requirement to support ARM noMMU processors like
Cortex-M3 and Cortex-M4.
 
>  Can't uClibc be fixed to enable interworking for the context functions so they
> will work even if the rest of the library is compiled in thumb mode?

I think the intention of this patch is to support thumb2 only
builds. There is no interworking support for Cortex-M3/Cortex-M4.
 
>  As I commented in v1 of this patch, as long as 0.9.33 is not killed, we can't
> do this. We could however add a condition on -ng.

Then I would suggest to add a condition on -ng.

I think there is some userbase for it, because I remember seeing the
third person trying to get something similar committed.

Best regards
 Waldemar

[Buildroot] [PATCH v2] package/uclibc: Enable compile in thumb mode configuration option

[Waldemar Brodkorb]

Hi Paul,
Paul Enman wrote,

> Hi All,
> Thanks for your feedback and insight. Buildroot does build a working Cortex-M
> (thumb instructions only) uClibc toolchain by touching up the uClibc(-ng)
> config file with
> 
> Enable COMPILE_IN_THUMB_MODE
> and
> Disable UCLIBC_HAS_CONTEXT_FUNCS
> 
> ARMv5 and thumb1 targets shouldn't be effected by this patch; I'll look into
> guarding packages that depend on (obsolescent?) context control functions and
> prepare an updated version for review.

I think some general symbol like BR2_ARCH_HAS_CONTEXT_FUNCS might be
useful, as other architectures like ARC/Xtensa do have the same
problem here.
 
> The toolchain compiles a bootable kernel and both Linuxthreads and NPTL build
> without error, however I am looking into why flthdr shows busybox bFLT flags
> are set to 0x2 (Has-PIC-GOT).

Is this a problem? What target do you use and did you do some
runtime testing on real hardware?

best regards
 Waldemar

[Buildroot] [PATCH v2] package/uclibc: Enable compile in thumb mode configuration option

[Waldemar Brodkorb]

Hi Arnout,
Arnout Vandecappelle wrote,

>  Hi Paul,
> 
>  [Please don't top-post, but reply inline like I do below.]
> 
> On 18-12-15 01:11, Paul Enman wrote:
> > Hi All,
> > Thanks for your feedback and insight. Buildroot does build a working Cortex-M
> > (thumb instructions only) uClibc toolchain by touching up the uClibc(-ng) config
> > file with
> > 
> > Enable COMPILE_IN_THUMB_MODE
> > and
> > Disable UCLIBC_HAS_CONTEXT_FUNCS
> > 
> > ARMv5 and thumb1 targets shouldn't be effected by this patch; I'll look into
> > guarding packages that depend on (obsolescent?) context control functions and
> > prepare an updated version for review.
> 
>  It will be quite hard to find such packages - especially longer term. There
> probably should be a thumb2 toolchain added to the autobuilders to cover this case.
> 
>  Also, finding a good explanation for the comment is going to be difficult...
> Something like "foo needs ARM instructions or a (e)glibc or musl toolchain".

Other architectures also have no support for context functions.
So a more general solution would be better. What packages use
context functions anyway?

best regards
 Waldemar

[Buildroot] [PATCH v2] package/uclibc: Enable compile in thumb mode configuration option

[Paul Enman]

Hi Thomas

On Tue, Dec 15, 2015 at 4:03 PM, Thomas Petazzoni <
thomas.petazzoni@free-electrons.com> wrote:

> Paul,
>
> On Sun, 13 Dec 2015 19:28:40 -0600, Paul Enman wrote:
> > From: penman <paul.enman@gmail.com>
>
> This is still not good, it should be your full name here as well.
>
Ok


>
> >
> > Signed-off-by: Paul Enman <paul.enman@gmail.com>
> > ---
> >
> > When buildroot is configured to build uClibc with thumb, it uses a
> workaround
> >  for that relies on interworking between arm and thumb instructions and
> does
> >  not set the config file to enable compile in thumb mode.
> >
> > This patch enables buildroot to configure and compile uClibc in thumb
> mode.
>
> Why do you put all these explanations after the "---" sign? They should
> really be part of the commit log.
>

The docs/manual/contribute.txt, Line 252 indicate this; I'll add to the
commit log.


>
> >
> >  arch/Config.in.arm       | 18 +++++++++---------
> >  package/uclibc/uclibc.mk | 12 ++++++++++++
> >  2 files changed, 21 insertions(+), 9 deletions(-)
> >
> > diff --git a/arch/Config.in.arm b/arch/Config.in.arm
> > index 67ff384..2d318f2 100644
> > --- a/arch/Config.in.arm
> > +++ b/arch/Config.in.arm
> > @@ -374,6 +374,15 @@ config BR2_ARM_INSTRUCTIONS_ARM
> >         This option instructs the compiler to generate regular ARM
> >         instructions, that are all 32 bits wide.
> >
> > +config BR2_ARM_INSTRUCTIONS_THUMB2
> > +     bool "Thumb2"
> > +     depends on BR2_ARM_CPU_HAS_THUMB2
> > +     help
> > +       This option instructions the compiler to generate Thumb2
> > +       instructions, which allows to mix 16 bits instructions and
> > +       32 bits instructions. This generally provides a much smaller
> > +       compiled binary size.
> > +
> >  config BR2_ARM_INSTRUCTIONS_THUMB
> >       bool "Thumb"
> >       depends on BR2_ARM_CPU_HAS_THUMB
> > @@ -389,15 +398,6 @@ comment "Thumb1 is not compatible with VFP"
> >       depends on BR2_ARM_CPU_HAS_THUMB
> >       depends on !BR2_ARM_SOFT_FLOAT
> >
> > -config BR2_ARM_INSTRUCTIONS_THUMB2
> > -     bool "Thumb2"
> > -     depends on BR2_ARM_CPU_HAS_THUMB2
> > -     help
> > -       This option instructions the compiler to generate Thumb2
> > -       instructions, which allows to mix 16 bits instructions and
> > -       32 bits instructions. This generally provides a much smaller
> > -       compiled binary size.
>
> I don't understand why you are re-ordering the options here. Why are
> you doing this?
>

I observed the default order of precedence for targets that support both
Thumb and Thumb2 (currently only Cortex-M3) is to default to Thumb(1), by
reordering, the default order would be ARM->Thumb2->Thumb as available.
This reordering is not necessary.
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[Buildroot] [PATCH v2] package/uclibc: Enable compile in thumb mode configuration option

[Paul Enman]

Hi Waldemar,

On Sat, Dec 19, 2015 at 3:13 AM, Waldemar Brodkorb <wbx@openadk.org> wrote:

> Hi Arnout,
> Arnout Vandecappelle wrote,
>
> > On 16-12-15 08:10, Waldemar Brodkorb wrote:
> > > Hi,
> > > Thomas Petazzoni wrote,
> > >> Paul,
> > >>
> > >>> + $(call KCONFIG_DISABLE_OPT,UCLIBC_HAS_CONTEXT_FUNCS,$(@D)/.config)
> > >>
> > >> What is the relation between this and Thumb ?
> > >
> > > The user context manipulation functions in uClibc are using
> > > non-thumb instructions and result in a compile failure.
> >
> >  Some packages need context functions, that's why they are enabled in our
> > default uClibc config. Cfr. d01aaa7 (by you, Waldemar).
>
> Yeah. But the context functions are deprecated and POSIX suggests
> not to use them. Unfortunately they are only implemented for
> arm/mips/x86/x86_64 in uClibc. Someone could port the implementation
> for other architectures from GNU libc. But then still all noMMU
> architectures would be missing. Furthermore the GNU libc
> implementation does not work for THUMB only builds.
>
> >  So if you do this, you'll need to make some packages depend on !THUMB.
> While
> > they actually did work before this commit.
>
> They did work before for people trying to run thumb code on a ARM
> core which allows both modes. (arm and thumb)
> But without this patch people can not use it to do a thumb2-only
> build, which is a requirement to support ARM noMMU processors like
> Cortex-M3 and Cortex-M4.
>
> >  Can't uClibc be fixed to enable interworking for the context functions
> so they
> > will work even if the rest of the library is compiled in thumb mode?
>
> I think the intention of this patch is to support thumb2 only
> builds. There is no interworking support for Cortex-M3/Cortex-M4.
>


> Best regards
>  Waldemar
>

Thanks for your insight, if I understand this correctly, context functions
are presently supported by toolchains using (e)glibc, musl and uClibc only
for architectures arm(with interworking)/mips/x86/x86_64 instructions (and
not thumb, thumb2, ARC, Xtensa, others)?
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