[PATCH] MIPS: microMIPS: Work around an assembler bug.

[PATCH] MIPS: microMIPS: Work around an assembler bug.

[Steven J. Hill]

From: "Steven J. Hill" <Steven.Hill@imgtec.com>

In newer toolchains, the 16-bit branch delay slot instruction
calculation is wrong. We get a message very similar to:

   {standard input}: Assembler messages:
   {standard input}:7035: Warning: wrong size instruction
   in a 16-bit branch delay slot

This corner case only occurs in 'arch/mips/kernel/traps.c' and
we add the '-fno-delayed-branch' option when compiling it.

Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com>
---
 arch/mips/kernel/Makefile |    8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
index 66c6705..76c8638 100644
--- a/arch/mips/kernel/Makefile
+++ b/arch/mips/kernel/Makefile
@@ -116,4 +116,12 @@ CFLAGS_branch.o			= $(CFLAGS_DSP)
 CFLAGS_ptrace.o			= $(CFLAGS_DSP)
 endif
 
+#
+# Workaround for newer toolchains when building microMIPS kernels.
+#
+ifeq ($(CONFIG_CPU_MICROMIPS), y)
+CFLAGS_traps.o    = $(shell if [ $(call cc-version) -gt 0407 ]; then \
+			echo $(call cc-option, -fno-delayed-branch); fi)
+endif
+
 CPPFLAGS_vmlinux.lds		:= $(KBUILD_CFLAGS)
-- 
1.7.10.4

Re: [PATCH] MIPS: microMIPS: Work around an assembler bug.

[Steven J. Hill]

On 04/07/2014 12:40 PM, Steven J. Hill wrote:
> From: "Steven J. Hill" <Steven.Hill@imgtec.com>
> 
> In newer toolchains, the 16-bit branch delay slot instruction
> calculation is wrong. We get a message very similar to:
> 
>    {standard input}: Assembler messages:
>    {standard input}:7035: Warning: wrong size instruction
>    in a 16-bit branch delay slot
> 
> This corner case only occurs in 'arch/mips/kernel/traps.c' and
> we add the '-fno-delayed-branch' option when compiling it.
> 
> Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com>
>
I rejected this in patchwork. Just making sure you do not use it.

Re: [PATCH] MIPS: microMIPS: Work around an assembler bug.

[Steven J. Hill]

On 04/07/2014 12:40 PM, Steven J. Hill wrote:
> From: "Steven J. Hill" <Steven.Hill@imgtec.com>
> 
> In newer toolchains, the 16-bit branch delay slot instruction
> calculation is wrong. We get a message very similar to:
> 
>    {standard input}: Assembler messages:
>    {standard input}:7035: Warning: wrong size instruction
>    in a 16-bit branch delay slot
> 
> This corner case only occurs in 'arch/mips/kernel/traps.c' and
> we add the '-fno-delayed-branch' option when compiling it.
> 
> Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com>
>
I rejected this in patchwork. Just making sure you do not use it.

Re: [PATCH] MIPS: microMIPS: Work around an assembler bug.

[Maciej W. Rozycki]

On Wed, 9 Apr 2014, Steven J. Hill wrote:

> > In newer toolchains, the 16-bit branch delay slot instruction
> > calculation is wrong. We get a message very similar to:
> > 
> >    {standard input}: Assembler messages:
> >    {standard input}:7035: Warning: wrong size instruction
> >    in a 16-bit branch delay slot
> > 
> > This corner case only occurs in 'arch/mips/kernel/traps.c' and
> > we add the '-fno-delayed-branch' option when compiling it.
> > 
> > Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com>
> >
> I rejected this in patchwork. Just making sure you do not use it.

 In any case I think using -mno-jals rather than -fno-delayed-branch would 
be a better workaround, wouldn't it?

  Maciej