On 14/11/2025 6:01 pm, Grygorii Strashko wrote:
From: Grygorii Strashko <[email protected]>
Now all libfdt features are built-it unconditionally, but...
X86: The libfdt is used on x86 only to parse Hyperlaunch/dom0less Xen
nodes, so full libfdt is not needed in this case and minimal, RO
configuration can be used.
ARM - situation is more complicated:
1) ARM reads Host DT (fdt.c RO)
2) ARM reads passthrough DT (RO)
3) ARM generates dom0/hwdom DT from Host DT (there is a mix of WIP and
SW APIs)
4) ARM generates domU DT (there is a mix of WIP and SW APIs)
4) With EFI enabled - ARM needs RW API and fdt_empty_tree
5) With CONFIG_OVERLAY_DTB - ARM needs RW and fdt_overlay API
Hence, add possibility for optimizing libfdt usage by introducing
separate
Kconfig options for each libfdt feature and select them where needed.
Following libfdt modules are not used after this change:
Makefile.libfdt
fdt_addresses.c
fdt_strerror.c
fdt_check.c
Signed-off-by: Grygorii Strashko <[email protected]>
---
Not sure about using DOMAIN_BUILD_HELPERS for selecting
LIBFDT features, as DOMAIN_BUILD_HELPERS doesn't exactly
says that domain's DT will be generated when selected.
xen/arch/arm/Kconfig | 4 ++++
xen/common/Kconfig | 4 ++++
xen/common/libfdt/Kconfig | 14 ++++++++++++++
xen/common/libfdt/Makefile | 12 +++++++++---
4 files changed, 31 insertions(+), 3 deletions(-)
create mode 100644 xen/common/libfdt/Kconfig
diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
index cf6af68299f6..f10cd3d7effc 100644
--- a/xen/arch/arm/Kconfig
+++ b/xen/arch/arm/Kconfig
@@ -111,6 +111,8 @@ config ARM_EFI
bool "UEFI boot service support"
depends on ARM_64 && !MPU
default y
+ select LIBFDT_RW
+ select LIBFDT_EMPTY_TREE
help
This option provides support for boot services through
UEFI firmware. A UEFI stub is provided to allow Xen to
@@ -149,6 +151,8 @@ config HAS_ITS
config OVERLAY_DTB
bool "DTB overlay support (UNSUPPORTED)" if UNSUPPORTED
depends on SYSCTL
+ select LIBFDT_RW
+ select LIBFDT_OVERLAY
help
Dynamic addition/removal of Xen device tree nodes using a dtbo.
diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index 401d5046f6f5..256aff269c3b 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -28,6 +28,8 @@ config DOM0LESS_BOOT
config DOMAIN_BUILD_HELPERS
bool
+ select LIBFDT_WIP
+ select LIBFDT_SW
config GRANT_TABLE
bool "Grant table support" if EXPERT
@@ -680,4 +682,6 @@ config PM_STATS
Enable collection of performance management statistics to aid in
analyzing and tuning power/performance characteristics of the
system
+source "common/libfdt/Kconfig"
+
endmenu
diff --git a/xen/common/libfdt/Kconfig b/xen/common/libfdt/Kconfig
new file mode 100644
index 000000000000..3abd904b2969
--- /dev/null
+++ b/xen/common/libfdt/Kconfig
@@ -0,0 +1,14 @@
+config LIBFDT_WIP
+ bool
+
+config LIBFDT_SW
+ bool
+
+config LIBFDT_RW
+ bool
+
+config LIBFDT_EMPTY_TREE
+ bool
+
+config LIBFDT_OVERLAY
+ bool
diff --git a/xen/common/libfdt/Makefile b/xen/common/libfdt/Makefile
index 6ce679f98f47..c832d1849a5c 100644
--- a/xen/common/libfdt/Makefile
+++ b/xen/common/libfdt/Makefile
@@ -1,7 +1,13 @@
-include $(src)/Makefile.libfdt
SECTIONS := text data $(SPECIAL_DATA_SECTIONS)
+obj-libfdt-y := fdt.o fdt_ro.o
+obj-libfdt-$(CONFIG_LIBFDT_WIP) += fdt_wip.o
+obj-libfdt-$(CONFIG_LIBFDT_SW) += fdt_sw.o
+obj-libfdt-$(CONFIG_LIBFDT_RW) += fdt_rw.o
+obj-libfdt-$(CONFIG_LIBFDT_EMPTY_TREE) += fdt_empty_tree.o
+obj-libfdt-$(CONFIG_LIBFDT_OVERLAY) += fdt_overlay.o
+
# For CONFIG_OVERLAY_DTB, libfdt functionalities will be needed
during runtime.
ifneq ($(CONFIG_OVERLAY_DTB),y)
OBJCOPYFLAGS := $(foreach s,$(SECTIONS),--rename-section
.$(s)=.init.$(s))
@@ -15,7 +21,7 @@ CFLAGS-y += -I$(srctree)/include/xen/libfdt/
$(obj)/libfdt.o: $(obj)/libfdt-temp.o FORCE
$(call if_changed,objcopy)
-$(obj)/libfdt-temp.o: $(addprefix $(obj)/,$(LIBFDT_OBJS)) FORCE
+$(obj)/libfdt-temp.o: $(addprefix $(obj)/,$(obj-libfdt-y)) FORCE
$(call if_changed,ld)
-targets += libfdt-temp.o $(LIBFDT_OBJS)
+targets += libfdt-temp.o $(obj-libfdt-y)
Pulling together several aspects.
Now that we have xen/lib, library stuff should be in it, including this
libfdt. I suggest moving it to xen/lib/fdt.
The build system problems are created by using non-standard rules to
bodge the init-ness. For livepatches, we have `init_or_livepatch` as
friends to do conditional init-ness. I'd suggest a similar approach
here.
You might want a prompt-less CONFIG_LIBFDT_NONINIT which can be
selected
by CONFIG_DTB_OVERLAY, because that's going to be better than trying to
make an implication directly about DTB_OVERLAY.
As to other issues hinted at:
* Init coverage. The only reason we don't have init coverage is
because
of the overly-restrictive SPECIAL_DATA_SECTIONS check, and while it
serves a purpose, it does a lot of harm too. It should be disabled by
things like CONFIG_COVERAGE so that we can retrieve coverage of boot
time paths, and because data placement is not interesting for these
types of builds.
* -f{function,data}-sections and --gc-sections. This gets dead
code/data elimination with better granularity than the translation
unit,
and removes the need for interior ifdefary to achieve the same
savings.
We already have -f*-sections for livepatching, so this is really just
using --gc-sections and will probably net a good win in one fell swoop.
~Andrew
