riscv: Gate FUNCTION_ALIGNMENT_4B on DYNAMIC_FTRACE

The FUNCTION_ALIGNMENT_4B select forces the whole kernel to be built
with -fmin-function-alignment=4. This alignment is only needed so the
patchable-function-entry NOPs, which arch/riscv/Makefile emits under
CONFIG_DYNAMIC_FTRACE, can be patched reliably on RISCV_ISA_C=y builds
where compressed instructions otherwise allow 2-byte function
alignment.

The select is currently gated on HAVE_DYNAMIC_FTRACE, a capability bit
that is selected whenever the toolchain supports dynamic ftrace, rather
than on whether tracing is actually enabled. As a result every
RISCV_ISA_C=y build gets 4-byte function alignment across the entire
kernel even when function tracing is disabled, needlessly growing the
kernel image and wasting instruction cache for a feature that is not
in use.

Gate the select on DYNAMIC_FTRACE instead, matching the condition under
which arch/riscv/Makefile emits -fpatchable-function-entry, so the
alignment is only applied when it is actually needed.

Fixes: c41bf4326c7b ("riscv: ftrace: align patchable functions to 4 Byte boundary")
Signed-off-by: Rui Qi <qirui.001@bytedance.com>
Link: https://patch.msgid.link/20260706130415.463682-1-qirui.001@bytedance.com
Signed-off-by: Paul Walmsley <pjw@kernel.org>

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index c0a6992933e411f745ef113df84a00ff7cf4a800..f7028caaeae06e093cb2b7e2f4733dfaf01af6ac 100644 (file)
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -157,7 +157,7 @@ config RISCV
        select HAVE_DEBUG_KMEMLEAK
        select HAVE_DMA_CONTIGUOUS if MMU
        select HAVE_DYNAMIC_FTRACE if MMU && (CLANG_SUPPORTS_DYNAMIC_FTRACE || GCC_SUPPORTS_DYNAMIC_FTRACE)
-       select FUNCTION_ALIGNMENT_4B if HAVE_DYNAMIC_FTRACE && RISCV_ISA_C
+       select FUNCTION_ALIGNMENT_4B if DYNAMIC_FTRACE && RISCV_ISA_C
        select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS if HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS
        select HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS if (DYNAMIC_FTRACE_WITH_ARGS && !CFI)
        select HAVE_DYNAMIC_FTRACE_WITH_ARGS if HAVE_DYNAMIC_FTRACE