[PATCH 3/4] kbuild: Allow LD_DEAD_CODE_DATA_ELIMINATION to be selectable if enabled

Nicholas Piggin
2018-04-20T07:34:42Z

Architectures that are capable can select
HAVE_LD_DEAD_CODE_DATA_ELIMINATION to enable selection of that
option (as an EXPERT kernel option).

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
arch/Kconfig | 15 ---------------
init/Kconfig | 27 +++++++++++++++++++++++++++
2 files changed, 27 insertions(+), 15 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 8e0d665c8d53..3234b73d4626 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -596,21 +596,6 @@ config CC_STACKPROTECTOR_AUTO

endchoice

-config LD_DEAD_CODE_DATA_ELIMINATION
- bool
- help
- Select this if the architecture wants to do dead code and
- data elimination with the linker by compiling with
- -ffunction-sections -fdata-sections and linking with
- --gc-sections.
-
- This requires that the arch annotates or otherwise protects
- its external entry points from being discarded. Linker scripts
- must also merge .text.*, .data.*, and .bss.* correctly into
- output sections. Care must be taken not to pull in unrelated
- sections (e.g., '.text.init'). Typically '.' in section names
- is used to distinguish them from label names / C identifiers.
-
config HAVE_ARCH_WITHIN_STACK_FRAMES
bool
help
diff --git a/init/Kconfig b/init/Kconfig
index f013afc74b11..1706d963766b 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1038,6 +1038,33 @@ config CC_OPTIMIZE_FOR_SIZE

endchoice

+config HAVE_LD_DEAD_CODE_DATA_ELIMINATION
+ bool
+ help
+ This requires that the arch annotates or otherwise protects
+ its external entry points from being discarded. Linker scripts
+ must also merge .text.*, .data.*, and .bss.* correctly into
+ output sections. Care must be taken not to pull in unrelated
+ sections (e.g., '.text.init'). Typically '.' in section names
+ is used to distinguish them from label names / C identifiers.
+
+config LD_DEAD_CODE_DATA_ELIMINATION
+ bool "Dead code and data elimination (EXPERIMENTAL)"
+ depends on HAVE_LD_DEAD_CODE_DATA_ELIMINATION
+ depends on EXPERT
+ help
+ Select this if the architecture wants to do dead code and
+ data elimination with the linker by compiling with
+ -ffunction-sections -fdata-sections, and linking with
+ --gc-sections.
+
+ This can reduce on disk and in-memory size of the kernel
+ code and static data, particularly for small configs and
+ on small systems. This has the possibility of introducing
+ silently broken kernel if the required annotations are not
+ present. This option is not well tested yet, so use at your
+ own risk.
+
config SYSCTL
bool

--
2.17.0