diff mbox series

[v6,13/25] kbuild: lto: merge module sections

Message ID 20201013003203.4168817-14-samitolvanen@google.com (mailing list archive)
State New, archived
Headers show
Series Add support for Clang LTO | expand

Commit Message

Sami Tolvanen Oct. 13, 2020, 12:31 a.m. UTC 
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>
---
 scripts/module.lds.S | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

Comments

Kees Cook Oct. 14, 2020, 10:49 p.m. UTC | #1 
On Mon, Oct 12, 2020 at 05:31:51PM -0700, Sami Tolvanen wrote:
> 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>
> ---
>  scripts/module.lds.S | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> diff --git a/scripts/module.lds.S b/scripts/module.lds.S
> index 69b9b71a6a47..037120173a22 100644
> --- a/scripts/module.lds.S
> +++ b/scripts/module.lds.S
> @@ -25,5 +25,33 @@ SECTIONS {
>  	__jump_table		0 : ALIGN(8) { KEEP(*(__jump_table)) }
>  }
>  
> +#ifdef CONFIG_LTO_CLANG

In looking at this again -- is this ifdef needed? Couldn't this be done
unconditionally? (Which would make it an independent change...)

-Kees

> +/*
> + * 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_]*) }
> +}
> +#endif
> +
>  /* bring in arch-specific sections */
>  #include <asm/module.lds.h>
> -- 
> 2.28.0.1011.ga647a8990f-goog
>
Sami Tolvanen Oct. 20, 2020, 4:42 p.m. UTC | #2 
On Wed, Oct 14, 2020 at 3:49 PM Kees Cook <keescook@chromium.org> wrote:
> In looking at this again -- is this ifdef needed? Couldn't this be done
> unconditionally? (Which would make it an independent change...)

No, I suppose it's not needed. I can drop the ifdef from the next version.

Sami
diff mbox series

Patch

diff --git a/scripts/module.lds.S b/scripts/module.lds.S
index 69b9b71a6a47..037120173a22 100644
--- a/scripts/module.lds.S
+++ b/scripts/module.lds.S
@@ -25,5 +25,33 @@  SECTIONS {
 	__jump_table		0 : ALIGN(8) { KEEP(*(__jump_table)) }
 }
 
+#ifdef CONFIG_LTO_CLANG
+/*
+ * 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_]*) }
+}
+#endif
+
 /* bring in arch-specific sections */
 #include <asm/module.lds.h>