[PATCH] riscv: ftrace: select HAVE_BUILDTIME_MCOUNT_SORT

[cp0613@linux.alibaba.com]

From: Chen Pei <cp0613@linux.alibaba.com>

RISC-V already satisfies all prerequisites for build-time mcount sorting:
the sorttable host tool handles EM_RISCV in its machine-type dispatch, and
the __mcount_loc section entries are stored as direct virtual addresses in
the final vmlinux binary, so no relocation processing is required during
the sort step.

Select HAVE_BUILDTIME_MCOUNT_SORT so that BUILDTIME_MCOUNT_SORT is
automatically enabled when DYNAMIC_FTRACE is configured.  This allows
sorttable to sort the __mcount_loc section at link time, making the
run-time ftrace initialisation path skip the software sort and reducing
kernel startup overhead.

Verified with CONFIG_FTRACE_SORT_STARTUP_TEST=y, which confirms that
the section produced by the build is already in ascending order:

  [    0.000000] ftrace section at ffffffff81015a60 sorted properly

Signed-off-by: Chen Pei <cp0613@linux.alibaba.com>
---
 arch/riscv/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 90c531e6abf5..6fe90591a274 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -151,6 +151,7 @@ config RISCV
 	select HAVE_ARCH_USERFAULTFD_WP if 64BIT && MMU && USERFAULTFD && RISCV_ISA_SVRSW60T59B
 	select HAVE_ARCH_VMAP_STACK if MMU && 64BIT
 	select HAVE_ASM_MODVERSIONS
+	select HAVE_BUILDTIME_MCOUNT_SORT
 	select HAVE_CONTEXT_TRACKING_USER
 	select HAVE_DEBUG_KMEMLEAK
 	select HAVE_DMA_CONTIGUOUS if MMU
-- 
2.50.1


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