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MIPS: Allow compact branch policy to be changed

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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: Paul 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: Ralf Baechle <ralf@linux-mips.org>
This commit is contained in:
Paul Burton 2015-09-22 10:07:41 -07:00 committed by Ralf Baechle
parent 05513992c6
commit c1a0e9bc88
2 changed files with 40 additions and 0 deletions
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36
arch/mips/Kconfig.debug
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@ -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

4
arch/mips/Makefile
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@ -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
#
# Firmware support
#