Commit c1a0e9bc authored by Paul Burton's avatar Paul Burton Committed by Ralf Baechle
Browse files

MIPS: Allow compact branch policy to be changed 



When debugging it can be helpful to change the policy for compiler use
of MIPSr6 compact branches, in order to rule out or home in on their
involvement in bugs. Allow the GCC -mcompact-branches= flag to be set
via Kconfig under the "Kernel hacking" menu.

Signed-off-by: default avatarPaul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/11178/


Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
parent 05513992

arch/mips/Kconfig.debug

+36 −0
Original line number Diff line number Diff line
@@ -113,4 +113,40 @@ config SPINLOCK_TEST 
	help

	  Add several files to the debugfs to test spinlock speed.



if CPU_MIPSR6



choice

	prompt "Compact branch policy"

	default MIPS_COMPACT_BRANCHES_OPTIMAL



config MIPS_COMPACT_BRANCHES_NEVER

	bool "Never (force delay slot branches)"

	help

	  Pass the -mcompact-branches=never flag to the compiler in order to

	  force it to always emit branches with delay slots, and make no use

	  of the compact branch instructions introduced by MIPSr6. This is

	  useful if you suspect there may be an issue with compact branches in

	  either the compiler or the CPU.



config MIPS_COMPACT_BRANCHES_OPTIMAL

	bool "Optimal (use where beneficial)"

	help

	  Pass the -mcompact-branches=optimal flag to the compiler in order for

	  it to make use of compact branch instructions where it deems them

	  beneficial, and use branches with delay slots elsewhere. This is the

	  default compiler behaviour, and should be used unless you have a

	  reason to choose otherwise.



config MIPS_COMPACT_BRANCHES_ALWAYS

	bool "Always (force compact branches)"

	help

	  Pass the -mcompact-branches=always flag to the compiler in order to

	  force it to always emit compact branches, making no use of branch

	  instructions with delay slots. This can result in more compact code

	  which may be beneficial in some scenarios.



endchoice



endif # CPU_MIPSR6



endmenu

arch/mips/Makefile

+4 −0
Original line number Diff line number Diff line
@@ -204,6 +204,10 @@ toolchain-msa := $(call cc-option-yn,$(mips-cflags) -mhard-float -mfp64 -Wa$( 
cflags-$(toolchain-msa)			+= -DTOOLCHAIN_SUPPORTS_MSA

endif



cflags-$(CONFIG_MIPS_COMPACT_BRANCHES_NEVER)	+= -mcompact-branches=never

cflags-$(CONFIG_MIPS_COMPACT_BRANCHES_OPTIMAL)	+= -mcompact-branches=optimal

cflags-$(CONFIG_MIPS_COMPACT_BRANCHES_ALWAYS)	+= -mcompact-branches=always



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