[PATCH v2 13/28] kbuild: lto: merge module sections

Sami Tolvanen
2020-09-03T20:38:04Z

LLD always splits sections with LTO, which increases module sizes. This
change adds a linker script that merges the split sections in the final
module.

Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
Makefile | 2 ++
scripts/module-lto.lds | 26 ++++++++++++++++++++++++++
2 files changed, 28 insertions(+)
create mode 100644 scripts/module-lto.lds

diff --git a/Makefile b/Makefile
index c69e07bd506a..bb82a4323f1d 100644
--- a/Makefile
+++ b/Makefile
@@ -921,6 +921,8 @@ CC_FLAGS_LTO_CLANG += -fvisibility=default
# Limit inlining across translation units to reduce binary size
LD_FLAGS_LTO_CLANG := -mllvm -import-instr-limit=5
KBUILD_LDFLAGS += $(LD_FLAGS_LTO_CLANG)
+
+KBUILD_LDS_MODULE += $(srctree)/scripts/module-lto.lds
endif

ifdef CONFIG_LTO
diff --git a/scripts/module-lto.lds b/scripts/module-lto.lds
new file mode 100644
index 000000000000..cbb11dc3639a
--- /dev/null
+++ b/scripts/module-lto.lds
@@ -0,0 +1,26 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * With CONFIG_LTO_CLANG, LLD always enables -fdata-sections and
+ * -ffunction-sections, which increases the size of the final module.
+ * Merge the split sections in the final binary.
+ */
+SECTIONS {
+ __patchable_function_entries : { *(__patchable_function_entries) }
+
+ .bss : {
+ *(.bss .bss.[0-9a-zA-Z_]*)
+ *(.bss..L*)
+ }
+
+ .data : {
+ *(.data .data.[0-9a-zA-Z_]*)
+ *(.data..L*)
+ }
+
+ .rodata : {
+ *(.rodata .rodata.[0-9a-zA-Z_]*)
+ *(.rodata..L*)
+ }
+
+ .text : { *(.text .text.[0-9a-zA-Z_]*) }
+}
--
2.28.0.402.g5ffc5be6b7-goog