Hi Jason,
On 09.12.25 23:47, Jason Andryuk wrote:
Add a new Kconfig CONFIG_GC_SECTIONS to control linking with
--gc-sections. --gc-sections witll garbage collect unused sections.
Combined with CONFIG_CC_SPLIT_SECTIONS, this will remove unreachable
code and data.
Linker scripts need to add KEEP() assorted places to retain
appropriate data - especially the arrays created by the linker script.
This has some affect, but it is inomplete. In a test where memory_add()
is unreachable, it is still included. I'm not sure, but it seems that
alternatives keep a relocation reference to it.
Only ELF xen is supported. xen.efi fails to link with many undefined
references when using --gc-sections.
Signed-off-by: Jason Andryuk <[email protected]>
---
v1:
Add Kconfig
select CC_SPLIT_SECTIONS
remove KEEP from .fixup
Add KEEP to .text.entry.* (Only needed with Jan's "common: honor
CONFIG_CC_SPLIT_SECTIONS also for assembly functions" ?)
Add ARM, RISC-V and PPC
Pipeline passes:
https://gitlab.com/xen-project/people/jandryuk-amd/xen/-/pipelines/2205223331
It defaults CONFIG_GC_SECTIONS=y and adds --print-gc-sections
[...]
---
xen/Makefile | 3 +++
xen/arch/arm/Makefile | 6 +++---
xen/arch/arm/xen.lds.S | 22 +++++++++++-----------
xen/arch/ppc/Makefile | 6 +++---
xen/arch/ppc/xen.lds.S | 14 +++++++-------
xen/arch/riscv/Makefile | 6 +++---
xen/arch/riscv/xen.lds.S | 14 +++++++-------
xen/arch/x86/Makefile | 6 +++---
xen/arch/x86/xen.lds.S | 34 +++++++++++++++++-----------------
xen/common/Kconfig | 9 +++++++++
xen/include/xen/xen.lds.h | 20 ++++++++++----------
11 files changed, 76 insertions(+), 64 deletions(-)
diff --git a/xen/Makefile b/xen/Makefile
index e6cf287425..aeb5dcf2ee 100644
--- a/xen/Makefile
+++ b/xen/Makefile
@@ -469,10 +469,13 @@ all-symbols-$(CONFIG_FAST_SYMBOL_LOOKUP) += --sort-by-name
include $(srctree)/arch/$(SRCARCH)/arch.mk
+XEN_FINAL_LDFLAGS-$(CONFIG_GC_SECTIONS) := --gc-sections
+
# define new variables to avoid the ones defined in Config.mk
export XEN_CFLAGS := $(CFLAGS)
export XEN_AFLAGS := $(AFLAGS)
export XEN_LDFLAGS := $(LDFLAGS)
+export XEN_FINAL_LDFLAGS := $(LDFLAGS) $(XEN_FINAL_LDFLAGS-y)
export CFLAGS_UBSAN
endif # need-config
[...]
diff --git a/xen/arch/arm/xen.lds.S b/xen/arch/arm/xen.lds.S
index 2d5f1c516d..178af612a2 100644
--- a/xen/arch/arm/xen.lds.S
+++ b/xen/arch/arm/xen.lds.S
@@ -63,7 +63,7 @@ SECTIONS
. = ALIGN(4);
__proc_info_start = .;
- *(.proc.info)
+ KEEP(*(.proc.info))
__proc_info_end = .;
} :text
@@ -103,7 +103,7 @@ SECTIONS
. = ALIGN(8);
.arch.info : {
_splatform = .;
- *(.arch.info)
+ KEEP(*(.arch.info))
_eplatform = .;
} :text
@@ -116,7 +116,7 @@ SECTIONS
. = ALIGN(8);
.teemediator.info : {
_steemediator = .;
- *(.teemediator.info)
+ KEEP(*(.teemediator.info))
_eteemediator = .;
} :text
@@ -127,7 +127,7 @@ SECTIONS
*(.init.text)
_einittext = .;
. = ALIGN(PAGE_SIZE); /* Avoid mapping alt insns executable */
- *(.altinstr_replacement)
+ KEEP(*(.altinstr_replacement))
} :text
. = ALIGN(PAGE_SIZE);
__init_data_begin = .;
@@ -137,18 +137,18 @@ SECTIONS
. = ALIGN(POINTER_ALIGN);
__setup_start = .;
- *(.init.setup)
+ KEEP(*(.init.setup))
__setup_end = .;
__initcall_start = .;
- *(.initcallpresmp.init)
+ KEEP(*(.initcallpresmp.init))
__presmp_initcall_end = .;
- *(.initcall1.init)
+ KEEP(*(.initcall1.init))
__initcall_end = .;
Wouldn't it be reasonable to do the same here for "initcall/setup" as was done
for
"schedulers_array"?
[...]
--
Best regards,
-grygorii
