[PATCH v1 6/7] DCE/DSE: riscv: add HAVE_TRIM_UNUSED_SYSCALLS support

[Zhangjin Wu]

For HAVE_TRIM_UNUSED_SYSCALLS, the syscall tables are hacked with the
inputing unused_syscalls.

Firstly, the intermediate preprocessed .i files are generated from the
original C version of syscall tables respectively, and named with a
'used' suffix: syscall_table_used.i, compat_syscall_table_used.i.

Secondly, all of the unused syscalls are commented.

At last, two new objective files sufixed with 'used' are generated from
the hacked .i files and they are linked into the eventual kernel image.

Signed-off-by: Zhangjin Wu <falcon@xxxxxxxxxxx>
---
 arch/riscv/Kconfig                  |  1 +
 arch/riscv/kernel/syscalls/Makefile | 37 +++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index d607ab0f7c6d..b5e726b49a6f 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -140,6 +140,7 @@ config RISCV
 	select HAVE_RSEQ
 	select HAVE_STACKPROTECTOR
 	select HAVE_SYSCALL_TRACEPOINTS
+	select HAVE_TRIM_UNUSED_SYSCALLS if HAVE_LD_DEAD_CODE_DATA_ELIMINATION
 	select HOTPLUG_CORE_SYNC_DEAD if HOTPLUG_CPU
 	select IRQ_DOMAIN
 	select IRQ_FORCED_THREADING
diff --git a/arch/riscv/kernel/syscalls/Makefile b/arch/riscv/kernel/syscalls/Makefile
index 65abd0871ee5..3b5969aaa9e8 100644
--- a/arch/riscv/kernel/syscalls/Makefile
+++ b/arch/riscv/kernel/syscalls/Makefile
@@ -3,8 +3,45 @@
 # Makefile for the RISC-V syscall tables
 #
 
+ifndef CONFIG_TRIM_UNUSED_SYSCALLS
+
 CFLAGS_syscall_table.o        += $(call cc-option,-Wno-override-init,)
 CFLAGS_compat_syscall_table.o += $(call cc-option,-Wno-override-init,)
 
 obj-y                += syscall_table.o
 obj-$(CONFIG_COMPAT) += compat_syscall_table.o
+else # CONFIG_TRIM_UNUSED_SYSCALLS
+
+include $(srctree)/scripts/Makefile.syscalls
+
+CFLAGS_syscall_table_used.o        += $(call cc-option,-Wno-override-init,)
+CFLAGS_compat_syscall_table_used.o += $(call cc-option,-Wno-override-init,)
+
+obj-y                += syscall_table_used.o
+obj-$(CONFIG_COMPAT) += compat_syscall_table_used.o
+
+# comment the unused syscalls
+quiet_cmd_used = USED    $@
+      cmd_used = sed -E -e '/^\[([0-9]+|\([0-9]+ \+ [0-9]+\))\] = /{/= *__riscv_(__sys_|sys_|compat_)*($(used_syscalls)),/!{s%^%/* %g;s%$$% */%g}}' -i $@;
+
+$(obj)/syscall_table_used.c: $(src)/syscall_table.c
+	$(Q)cp $< $@
+
+$(obj)/syscall_table_used.i: $(src)/syscall_table_used.c $(used_syscalls_deps) FORCE
+	$(call if_changed_dep,cpp_i_c)
+	$(call cmd,used)
+
+$(obj)/syscall_table_used.o: $(obj)/syscall_table_used.i FORCE
+	$(call if_changed,cc_o_c)
+
+$(obj)/compat_syscall_table_used.c: $(src)/compat_syscall_table.c
+	$(Q)cp $< $@
+
+$(obj)/compat_syscall_table_used.i: $(src)/compat_syscall_table_used.c $(used_syscalls_deps) FORCE
+	$(call if_changed_dep,cpp_i_c)
+	$(call cmd,used)
+
+$(obj)/compat_syscall_table_used.o: $(obj)/compat_syscall_table_used.i FORCE
+	$(call if_changed,cc_o_c)
+
+endif # CONFIG_TRIM_UNUSED_SYSCALLS
-- 
2.25.1