kbuild: lto: merge module sections

commit dd27762 upstream.

LLD always splits sections with LTO, which increases module sizes. This
change adds linker script rules to merge the split sections in the final
module.

Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20201211184633.3213045-6-samitolvanen@google.com
Cc: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

scripts/module.lds.S

@@ -23,6 +23,30 @@ SECTIONS {
 	.init_array		0 : ALIGN(8) { *(SORT(.init_array.*)) *(.init_array) }
 
 	__jump_table		0 : ALIGN(8) { KEEP(*(__jump_table)) }
+
+	__patchable_function_entries : { *(__patchable_function_entries) }
+
+	/*
+	 * 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.
+	 */
+	.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_]*) }
 }
 
 /* bring in arch-specific sections */