ANDROID: kbuild: merge module sections with LTO

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.

Bug: 145297228
Change-Id: I247e8bd029bd0f98a4fa1cd4db7f6398467b8e55
Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>

Makefile

@@ -839,6 +839,8 @@ lto-clang-flags	:= -flto
 endif
 lto-clang-flags += -fvisibility=default $(call cc-option, -fsplit-lto-unit)
 
+KBUILD_LDS_MODULE += $(srctree)/scripts/module-lto.lds
+
 # allow disabling only clang LTO where needed
 DISABLE_LTO_CLANG := -fno-lto
 export DISABLE_LTO_CLANG

scripts/module-lto.lds

@@ -0,0 +1,22 @@
+/*
+ * 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 {
+	/*
+	 * LLVM may emit .eh_frame with CONFIG_CFI_CLANG despite
+	 * -fno-asynchronous-unwind-tables. Discard the section.
+	 */
+	/DISCARD/ : {
+		*(.eh_frame)
+	}
+
+	.bss : { *(.bss .bss[.0-9a-zA-Z_]*) }
+	.data : { *(.data .data[.0-9a-zA-Z_]*) }
+	.rela.data : { *(.rela.data .rela.data[.0-9a-zA-Z_]*) }
+	.rela.rodata : { *(.rela.rodata .rela.rodata[.0-9a-zA-Z_]*) }
+	.rela.text : { *(.rela.text .rela.text[.0-9a-zA-Z_]*) }
+	.rodata : { *(.rodata .rodata[.0-9a-zA-Z_]*) }
+	.text : { *(.text .text[.0-9a-zA-Z_]*) }
+}