kbuild: lto: merge module sections

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

diff --git a/scripts/module.lds.S b/scripts/module.lds.S
index 69b9b71..18d5b84 100644 (file)
--- a/scripts/module.lds.S
+++ b/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 */