Patchwork [U-Boot,v2,2/2] arm: work around assembler bug

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Submitter Allen Martin
Date July 10, 2012, 5 p.m.
Message ID <1341939617-26450-2-git-send-email-amartin@nvidia.com>
Download mbox | patch
Permalink /patch/170252/
State Changes Requested
Headers show

Comments

Allen Martin - July 10, 2012, 5 p.m.
Disable sibling call optimization based on binutils version.  This is
to work around a bug in the assember in binutils versions < 2.22.
Branches to weak symbols can be incorrectly optimized in thumb mode to
a short branch (b.n instruction) that won't reach when the symbol gets
preempted.

http://sourceware.org/bugzilla/show_bug.cgi?id=12532

Signed-off-by: Allen Martin <amartin@nvidia.com>
---
changes for v2:
 -changed GAS_BUG_12532 from yes/no to y/n to be consistent
 -added additional warning about code size increase
---
 arch/arm/config.mk |   21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)
Tom Rini - July 10, 2012, 5:25 p.m.
On Tue, Jul 10, 2012 at 10:00:17AM -0700, Allen Martin wrote:
> Disable sibling call optimization based on binutils version.  This is
> to work around a bug in the assember in binutils versions < 2.22.
> Branches to weak symbols can be incorrectly optimized in thumb mode to
> a short branch (b.n instruction) that won't reach when the symbol gets
> preempted.
> 
> http://sourceware.org/bugzilla/show_bug.cgi?id=12532
> 
> Signed-off-by: Allen Martin <amartin@nvidia.com>
> ---
> changes for v2:
>  -changed GAS_BUG_12532 from yes/no to y/n to be consistent
>  -added additional warning about code size increase
> ---
>  arch/arm/config.mk |   21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/arch/arm/config.mk b/arch/arm/config.mk
> index 3f4453a..bcabf17 100644
> --- a/arch/arm/config.mk
> +++ b/arch/arm/config.mk
> @@ -87,3 +87,24 @@ endif
>  ifndef CONFIG_NAND_SPL
>  LDFLAGS_u-boot += -pie
>  endif
> +
> +#
> +# binutils versions < 2.22 have a bug in the assembler where branches
> +# to weak symbols can be incorrectly optimized in thumb mode to a
> +# short branch (b.n instruction) that won't reach when the symbol
> +# gets preempted
> +#
> +# http://sourceware.org/bugzilla/show_bug.cgi?id=12532
> +#
> +ifeq ($(CONFIG_SYS_THUMB_BUILD),y)
> +ifeq ($(GAS_BUG_12532),)
> +export GAS_BUG_12532:=$(shell if [ $(call binutils-version) -lt 0222 ] ; then echo y; else echo n; fi)

Please don't squash out whitespace, just break this out into a
multi-line test ala the others in the toplevel config.mk.

> +ifeq ($(GAS_BUG_12532),y)
> +$(warning *** disabling sibling call optimzation because binutils version < 2.22)
> +$(warning *** code size may be slightly larger)
> +endif
> +endif
> +ifeq ($(GAS_BUG_12532),y)
> +PLATFORM_RELFLAGS += -fno-optimize-sibling-calls
> +endif
> +endif

This seems a bit longer than needed.  Just check that it's y once and do
both things.  Also, I _think_ we should be able to squish this down to:
ifeq ($(CONFIG_SYS_THUMB_BUILD),y)
GAS_BUG_12532 := $(shell if [ $(call binutils-version) -lt 0222 ] ; \
	then echo y; else echo n; fi)
ifeq ($(GAS_BUG_125320),y)
$(warning ...)
$(warning ...)
PLATFORM_RELFLAGS += ...
endif
endif

But I haven't tested it.
Allen Martin - July 10, 2012, 5:44 p.m.
On Tue, Jul 10, 2012 at 10:25:05AM -0700, Tom Rini wrote:
> * PGP Signed by an unknown key
> 
> On Tue, Jul 10, 2012 at 10:00:17AM -0700, Allen Martin wrote:
> > Disable sibling call optimization based on binutils version.  This is
> > to work around a bug in the assember in binutils versions < 2.22.
> > Branches to weak symbols can be incorrectly optimized in thumb mode to
> > a short branch (b.n instruction) that won't reach when the symbol gets
> > preempted.
> > 
> > http://sourceware.org/bugzilla/show_bug.cgi?id=12532
> > 
> > Signed-off-by: Allen Martin <amartin@nvidia.com>
> > ---
> > changes for v2:
> >  -changed GAS_BUG_12532 from yes/no to y/n to be consistent
> >  -added additional warning about code size increase
> > ---
> >  arch/arm/config.mk |   21 +++++++++++++++++++++
> >  1 file changed, 21 insertions(+)
> > 
> > diff --git a/arch/arm/config.mk b/arch/arm/config.mk
> > index 3f4453a..bcabf17 100644
> > --- a/arch/arm/config.mk
> > +++ b/arch/arm/config.mk
> > @@ -87,3 +87,24 @@ endif
> >  ifndef CONFIG_NAND_SPL
> >  LDFLAGS_u-boot += -pie
> >  endif
> > +
> > +#
> > +# binutils versions < 2.22 have a bug in the assembler where branches
> > +# to weak symbols can be incorrectly optimized in thumb mode to a
> > +# short branch (b.n instruction) that won't reach when the symbol
> > +# gets preempted
> > +#
> > +# http://sourceware.org/bugzilla/show_bug.cgi?id=12532
> > +#
> > +ifeq ($(CONFIG_SYS_THUMB_BUILD),y)
> > +ifeq ($(GAS_BUG_12532),)
> > +export GAS_BUG_12532:=$(shell if [ $(call binutils-version) -lt 0222 ] ; then echo y; else echo n; fi)
> 
> Please don't squash out whitespace, just break this out into a
> multi-line test ala the others in the toplevel config.mk.

Ok

> > +ifeq ($(GAS_BUG_12532),y)
> > +$(warning *** disabling sibling call optimzation because binutils version < 2.22)
> > +$(warning *** code size may be slightly larger)
> > +endif
> > +endif
> > +ifeq ($(GAS_BUG_12532),y)
> > +PLATFORM_RELFLAGS += -fno-optimize-sibling-calls
> > +endif
> > +endif
> 
> This seems a bit longer than needed.  Just check that it's y once and do
> both things.  Also, I _think_ we should be able to squish this down to:
> ifeq ($(CONFIG_SYS_THUMB_BUILD),y)
> GAS_BUG_12532 := $(shell if [ $(call binutils-version) -lt 0222 ] ; \
> 	then echo y; else echo n; fi)
> ifeq ($(GAS_BUG_125320),y)
> $(warning ...)
> $(warning ...)
> PLATFORM_RELFLAGS += ...
> endif
> endif
> 
> But I haven't tested it.

I wrote it the way I did because I only want the expensive
shell/binutils-version to get evaluated once per "make".  I think what
you proposed would cause it to get re-evaluated every time the build
goes down into a subdir.

-Allen
Tom Rini - July 10, 2012, 5:50 p.m.
On Tue, Jul 10, 2012 at 10:44:33AM -0700, Allen Martin wrote:
> On Tue, Jul 10, 2012 at 10:25:05AM -0700, Tom Rini wrote:
> > * PGP Signed by an unknown key
> > 
> > On Tue, Jul 10, 2012 at 10:00:17AM -0700, Allen Martin wrote:
> > > Disable sibling call optimization based on binutils version.  This is
> > > to work around a bug in the assember in binutils versions < 2.22.
> > > Branches to weak symbols can be incorrectly optimized in thumb mode to
> > > a short branch (b.n instruction) that won't reach when the symbol gets
> > > preempted.
> > > 
> > > http://sourceware.org/bugzilla/show_bug.cgi?id=12532
> > > 
> > > Signed-off-by: Allen Martin <amartin@nvidia.com>
> > > ---
> > > changes for v2:
> > >  -changed GAS_BUG_12532 from yes/no to y/n to be consistent
> > >  -added additional warning about code size increase
> > > ---
> > >  arch/arm/config.mk |   21 +++++++++++++++++++++
> > >  1 file changed, 21 insertions(+)
> > > 
> > > diff --git a/arch/arm/config.mk b/arch/arm/config.mk
> > > index 3f4453a..bcabf17 100644
> > > --- a/arch/arm/config.mk
> > > +++ b/arch/arm/config.mk
> > > @@ -87,3 +87,24 @@ endif
> > >  ifndef CONFIG_NAND_SPL
> > >  LDFLAGS_u-boot += -pie
> > >  endif
> > > +
> > > +#
> > > +# binutils versions < 2.22 have a bug in the assembler where branches
> > > +# to weak symbols can be incorrectly optimized in thumb mode to a
> > > +# short branch (b.n instruction) that won't reach when the symbol
> > > +# gets preempted
> > > +#
> > > +# http://sourceware.org/bugzilla/show_bug.cgi?id=12532
> > > +#
> > > +ifeq ($(CONFIG_SYS_THUMB_BUILD),y)
> > > +ifeq ($(GAS_BUG_12532),)
> > > +export GAS_BUG_12532:=$(shell if [ $(call binutils-version) -lt 0222 ] ; then echo y; else echo n; fi)
> > 
> > Please don't squash out whitespace, just break this out into a
> > multi-line test ala the others in the toplevel config.mk.
> 
> Ok
> 
> > > +ifeq ($(GAS_BUG_12532),y)
> > > +$(warning *** disabling sibling call optimzation because binutils version < 2.22)
> > > +$(warning *** code size may be slightly larger)
> > > +endif
> > > +endif
> > > +ifeq ($(GAS_BUG_12532),y)
> > > +PLATFORM_RELFLAGS += -fno-optimize-sibling-calls
> > > +endif
> > > +endif
> > 
> > This seems a bit longer than needed.  Just check that it's y once and do
> > both things.  Also, I _think_ we should be able to squish this down to:
> > ifeq ($(CONFIG_SYS_THUMB_BUILD),y)
> > GAS_BUG_12532 := $(shell if [ $(call binutils-version) -lt 0222 ] ; \
> > 	then echo y; else echo n; fi)
> > ifeq ($(GAS_BUG_125320),y)
> > $(warning ...)
> > $(warning ...)
> > PLATFORM_RELFLAGS += ...
> > endif
> > endif
> > 
> > But I haven't tested it.
> 
> I wrote it the way I did because I only want the expensive
> shell/binutils-version to get evaluated once per "make".  I think what
> you proposed would cause it to get re-evaluated every time the build
> goes down into a subdir.

It should still get evaluated once, I think.  Kluding the
binutils-version script to echo 1 >> /tmp/test every time it's run would
tell tho for sure :)
Allen Martin - July 10, 2012, 6:04 p.m.
On Tue, Jul 10, 2012 at 10:50:34AM -0700, Tom Rini wrote:
> On Tue, Jul 10, 2012 at 10:44:33AM -0700, Allen Martin wrote:
> > On Tue, Jul 10, 2012 at 10:25:05AM -0700, Tom Rini wrote:
> > > * PGP Signed by an unknown key
> > > 
> > > On Tue, Jul 10, 2012 at 10:00:17AM -0700, Allen Martin wrote:
> > > > Disable sibling call optimization based on binutils version.  This is
> > > > to work around a bug in the assember in binutils versions < 2.22.
> > > > Branches to weak symbols can be incorrectly optimized in thumb mode to
> > > > a short branch (b.n instruction) that won't reach when the symbol gets
> > > > preempted.
> > > > 
> > > > http://sourceware.org/bugzilla/show_bug.cgi?id=12532
> > > > 
> > > > Signed-off-by: Allen Martin <amartin@nvidia.com>
> > > > ---
> > > > changes for v2:
> > > >  -changed GAS_BUG_12532 from yes/no to y/n to be consistent
> > > >  -added additional warning about code size increase
> > > > ---
> > > >  arch/arm/config.mk |   21 +++++++++++++++++++++
> > > >  1 file changed, 21 insertions(+)
> > > > 
> > > > diff --git a/arch/arm/config.mk b/arch/arm/config.mk
> > > > index 3f4453a..bcabf17 100644
> > > > --- a/arch/arm/config.mk
> > > > +++ b/arch/arm/config.mk
> > > > @@ -87,3 +87,24 @@ endif
> > > >  ifndef CONFIG_NAND_SPL
> > > >  LDFLAGS_u-boot += -pie
> > > >  endif
> > > > +
> > > > +#
> > > > +# binutils versions < 2.22 have a bug in the assembler where branches
> > > > +# to weak symbols can be incorrectly optimized in thumb mode to a
> > > > +# short branch (b.n instruction) that won't reach when the symbol
> > > > +# gets preempted
> > > > +#
> > > > +# http://sourceware.org/bugzilla/show_bug.cgi?id=12532
> > > > +#
> > > > +ifeq ($(CONFIG_SYS_THUMB_BUILD),y)
> > > > +ifeq ($(GAS_BUG_12532),)
> > > > +export GAS_BUG_12532:=$(shell if [ $(call binutils-version) -lt 0222 ] ; then echo y; else echo n; fi)
> > > 
> > > Please don't squash out whitespace, just break this out into a
> > > multi-line test ala the others in the toplevel config.mk.
> > 
> > Ok
> > 
> > > > +ifeq ($(GAS_BUG_12532),y)
> > > > +$(warning *** disabling sibling call optimzation because binutils version < 2.22)
> > > > +$(warning *** code size may be slightly larger)
> > > > +endif
> > > > +endif
> > > > +ifeq ($(GAS_BUG_12532),y)
> > > > +PLATFORM_RELFLAGS += -fno-optimize-sibling-calls
> > > > +endif
> > > > +endif
> > > 
> > > This seems a bit longer than needed.  Just check that it's y once and do
> > > both things.  Also, I _think_ we should be able to squish this down to:
> > > ifeq ($(CONFIG_SYS_THUMB_BUILD),y)
> > > GAS_BUG_12532 := $(shell if [ $(call binutils-version) -lt 0222 ] ; \
> > > 	then echo y; else echo n; fi)
> > > ifeq ($(GAS_BUG_125320),y)
> > > $(warning ...)
> > > $(warning ...)
> > > PLATFORM_RELFLAGS += ...
> > > endif
> > > endif
> > > 
> > > But I haven't tested it.
> > 
> > I wrote it the way I did because I only want the expensive
> > shell/binutils-version to get evaluated once per "make".  I think what
> > you proposed would cause it to get re-evaluated every time the build
> > goes down into a subdir.
> 
> It should still get evaluated once, I think.  Kluding the
> binutils-version script to echo 1 >> /tmp/test every time it's run would
> tell tho for sure :)

I tried it out, it's obvious from the $(warning) it's getting
reevaluated:

$ ./MAKEALL -s tegra20
/home/arm/u-boot/arch/arm/config.mk:102: *** disabling sibling call optimzation because binutils version < 2.22
/home/arm/u-boot/arch/arm/config.mk:103: *** code size may be slightly larger
Configuring for harmony board...
   text    data     bss     dec     hex filename
 170334    4284  278352  452970   6e96a ./u-boot
  11676     161      36   11873    2e61 ./spl/u-boot-spl
/home/arm/u-boot/arch/arm/config.mk:102: *** disabling sibling call optimzation because binutils version < 2.22
/home/arm/u-boot/arch/arm/config.mk:103: *** code size may be slightly larger
/home/arm/u-boot/arch/arm/config.mk:102: *** disabling sibling call optimzation because binutils version < 2.22
/home/arm/u-boot/arch/arm/config.mk:103: *** code size may be slightly larger
/home/arm/u-boot/arch/arm/config.mk:102: *** disabling sibling call optimzation because binutils version < 2.22
/home/arm/u-boot/arch/arm/config.mk:103: *** code size may be slightly larger
/home/arm/u-boot/arch/arm/config.mk:102: *** disabling sibling call optimzation because binutils version < 2.22
/home/arm/u-boot/arch/arm/config.mk:103: *** code size may be slightly larger
/home/arm/u-boot/arch/arm/config.mk:102: *** disabling sibling call optimzation because binutils version < 2.22
/home/arm/u-boot/arch/arm/config.mk:103: *** code size may be slightly larger
/home/arm/u-boot/arch/arm/config.mk:102: *** disabling sibling call optimzation because binutils version < 2.22
/home/arm/u-boot/arch/arm/config.mk:103: *** code size may be slightly larger
... and on and on


It makes sense since unless GAS_BUG_125320 is "export"ed to the new
make, it's going to be unset again each the build starts a new
"make -C" 

-Allen
Tom Rini - July 10, 2012, 6:11 p.m.
On Tue, Jul 10, 2012 at 11:04:50AM -0700, Allen Martin wrote:
> On Tue, Jul 10, 2012 at 10:50:34AM -0700, Tom Rini wrote:
> > On Tue, Jul 10, 2012 at 10:44:33AM -0700, Allen Martin wrote:
> > > On Tue, Jul 10, 2012 at 10:25:05AM -0700, Tom Rini wrote:
> > > > * PGP Signed by an unknown key
> > > > 
> > > > On Tue, Jul 10, 2012 at 10:00:17AM -0700, Allen Martin wrote:
> > > > > Disable sibling call optimization based on binutils version.  This is
> > > > > to work around a bug in the assember in binutils versions < 2.22.
> > > > > Branches to weak symbols can be incorrectly optimized in thumb mode to
> > > > > a short branch (b.n instruction) that won't reach when the symbol gets
> > > > > preempted.
> > > > > 
> > > > > http://sourceware.org/bugzilla/show_bug.cgi?id=12532
> > > > > 
> > > > > Signed-off-by: Allen Martin <amartin@nvidia.com>
> > > > > ---
> > > > > changes for v2:
> > > > >  -changed GAS_BUG_12532 from yes/no to y/n to be consistent
> > > > >  -added additional warning about code size increase
> > > > > ---
> > > > >  arch/arm/config.mk |   21 +++++++++++++++++++++
> > > > >  1 file changed, 21 insertions(+)
> > > > > 
> > > > > diff --git a/arch/arm/config.mk b/arch/arm/config.mk
> > > > > index 3f4453a..bcabf17 100644
> > > > > --- a/arch/arm/config.mk
> > > > > +++ b/arch/arm/config.mk
> > > > > @@ -87,3 +87,24 @@ endif
> > > > >  ifndef CONFIG_NAND_SPL
> > > > >  LDFLAGS_u-boot += -pie
> > > > >  endif
> > > > > +
> > > > > +#
> > > > > +# binutils versions < 2.22 have a bug in the assembler where branches
> > > > > +# to weak symbols can be incorrectly optimized in thumb mode to a
> > > > > +# short branch (b.n instruction) that won't reach when the symbol
> > > > > +# gets preempted
> > > > > +#
> > > > > +# http://sourceware.org/bugzilla/show_bug.cgi?id=12532
> > > > > +#
> > > > > +ifeq ($(CONFIG_SYS_THUMB_BUILD),y)
> > > > > +ifeq ($(GAS_BUG_12532),)
> > > > > +export GAS_BUG_12532:=$(shell if [ $(call binutils-version) -lt 0222 ] ; then echo y; else echo n; fi)
> > > > 
> > > > Please don't squash out whitespace, just break this out into a
> > > > multi-line test ala the others in the toplevel config.mk.
> > > 
> > > Ok
> > > 
> > > > > +ifeq ($(GAS_BUG_12532),y)
> > > > > +$(warning *** disabling sibling call optimzation because binutils version < 2.22)
> > > > > +$(warning *** code size may be slightly larger)
> > > > > +endif
> > > > > +endif
> > > > > +ifeq ($(GAS_BUG_12532),y)
> > > > > +PLATFORM_RELFLAGS += -fno-optimize-sibling-calls
> > > > > +endif
> > > > > +endif
> > > > 
> > > > This seems a bit longer than needed.  Just check that it's y once and do
> > > > both things.  Also, I _think_ we should be able to squish this down to:
> > > > ifeq ($(CONFIG_SYS_THUMB_BUILD),y)
> > > > GAS_BUG_12532 := $(shell if [ $(call binutils-version) -lt 0222 ] ; \
> > > > 	then echo y; else echo n; fi)
> > > > ifeq ($(GAS_BUG_125320),y)
> > > > $(warning ...)
> > > > $(warning ...)
> > > > PLATFORM_RELFLAGS += ...
> > > > endif
> > > > endif
> > > > 
> > > > But I haven't tested it.
> > > 
> > > I wrote it the way I did because I only want the expensive
> > > shell/binutils-version to get evaluated once per "make".  I think what
> > > you proposed would cause it to get re-evaluated every time the build
> > > goes down into a subdir.
> > 
> > It should still get evaluated once, I think.  Kluding the
> > binutils-version script to echo 1 >> /tmp/test every time it's run would
> > tell tho for sure :)
> 
> I tried it out, it's obvious from the $(warning) it's getting
> reevaluated:
> 
> $ ./MAKEALL -s tegra20
> /home/arm/u-boot/arch/arm/config.mk:102: *** disabling sibling call optimzation because binutils version < 2.22
> /home/arm/u-boot/arch/arm/config.mk:103: *** code size may be slightly larger
> Configuring for harmony board...
>    text    data     bss     dec     hex filename
>  170334    4284  278352  452970   6e96a ./u-boot
>   11676     161      36   11873    2e61 ./spl/u-boot-spl
> /home/arm/u-boot/arch/arm/config.mk:102: *** disabling sibling call optimzation because binutils version < 2.22
> /home/arm/u-boot/arch/arm/config.mk:103: *** code size may be slightly larger
> /home/arm/u-boot/arch/arm/config.mk:102: *** disabling sibling call optimzation because binutils version < 2.22
> /home/arm/u-boot/arch/arm/config.mk:103: *** code size may be slightly larger
> /home/arm/u-boot/arch/arm/config.mk:102: *** disabling sibling call optimzation because binutils version < 2.22
> /home/arm/u-boot/arch/arm/config.mk:103: *** code size may be slightly larger
> /home/arm/u-boot/arch/arm/config.mk:102: *** disabling sibling call optimzation because binutils version < 2.22
> /home/arm/u-boot/arch/arm/config.mk:103: *** code size may be slightly larger
> /home/arm/u-boot/arch/arm/config.mk:102: *** disabling sibling call optimzation because binutils version < 2.22
> /home/arm/u-boot/arch/arm/config.mk:103: *** code size may be slightly larger
> /home/arm/u-boot/arch/arm/config.mk:102: *** disabling sibling call optimzation because binutils version < 2.22
> /home/arm/u-boot/arch/arm/config.mk:103: *** code size may be slightly larger
> ... and on and on
> 
> 
> It makes sense since unless GAS_BUG_125320 is "export"ed to the new
> make, it's going to be unset again each the build starts a new
> "make -C" 

Thanks for proving me wrong.  Just the white-space / multi line thing
please, thanks :)

Patch

diff --git a/arch/arm/config.mk b/arch/arm/config.mk
index 3f4453a..bcabf17 100644
--- a/arch/arm/config.mk
+++ b/arch/arm/config.mk
@@ -87,3 +87,24 @@  endif
 ifndef CONFIG_NAND_SPL
 LDFLAGS_u-boot += -pie
 endif
+
+#
+# binutils versions < 2.22 have a bug in the assembler where branches
+# to weak symbols can be incorrectly optimized in thumb mode to a
+# short branch (b.n instruction) that won't reach when the symbol
+# gets preempted
+#
+# http://sourceware.org/bugzilla/show_bug.cgi?id=12532
+#
+ifeq ($(CONFIG_SYS_THUMB_BUILD),y)
+ifeq ($(GAS_BUG_12532),)
+export GAS_BUG_12532:=$(shell if [ $(call binutils-version) -lt 0222 ] ; then echo y; else echo n; fi)
+ifeq ($(GAS_BUG_12532),y)
+$(warning *** disabling sibling call optimzation because binutils version < 2.22)
+$(warning *** code size may be slightly larger)
+endif
+endif
+ifeq ($(GAS_BUG_12532),y)
+PLATFORM_RELFLAGS += -fno-optimize-sibling-calls
+endif
+endif