[XEN][PATCH v2] coverage: extend coverage on .init and lib code

[Grygorii Strashko <grygorii_strashko@xxxxxxxx>]

From: Grygorii Strashko <grygorii_strashko@xxxxxxxx>

Extend coverage support on .init and lib code.
Add two hidden Kconfig options:
- RELAX_INIT_CHECK "Relax strict check for .init sections only in %.init.o
files"
- DO_NOT_FREE_INIT_MEMORY "Prevent freeing of .init sections at the end of
Xen boot."

Both selected selected when COVERAGE=y, as getting coverage report for
".init" code is required:
- to bypass strict check for .init sections only in %.init.o files;
- the .init code stay in memory after Xen boot.

RELAX_INIT_CHECK/DO_NOT_FREE_INIT_MEMORY could be used by other debug
features in the future.

Signed-off-by: Grygorii Strashko <grygorii_strashko@xxxxxxxx>
---
changes in v2:
 - add RELAX_INIT_CHECK and DO_NOT_FREE_INIT_MEMORY, those are two different 
things,
   both potentially reusable
 - enable coverage for libfdt/libelf always
 - enable colverage for .init always
 
v1: 
https://patchwork.kernel.org/project/xen-devel/patch/20251203222436.660044-1-grygorii_strashko@xxxxxxxx/

 xen/Kconfig.debug          | 12 ++++++++++++
 xen/Rules.mk               | 10 ++++++++--
 xen/arch/arm/setup.c       |  2 ++
 xen/arch/x86/setup.c       |  4 ++++
 xen/common/libelf/Makefile |  1 -
 xen/common/libfdt/Makefile |  1 -
 6 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/xen/Kconfig.debug b/xen/Kconfig.debug
index d900d926c555..8fc201d12c2c 100644
--- a/xen/Kconfig.debug
+++ b/xen/Kconfig.debug
@@ -39,11 +39,23 @@ config COVERAGE
        bool "Code coverage support"
        depends on SYSCTL && !LIVEPATCH
        select SUPPRESS_DUPLICATE_SYMBOL_WARNINGS if !ENFORCE_UNIQUE_SYMBOLS
+       select RELAX_INIT_CHECK
+       select DO_NOT_FREE_INIT_MEMORY
        help
          Enable code coverage support.
 
          If unsure, say N here.
 
+config RELAX_INIT_CHECK
+    bool
+    help
+      Relax strict check for .init sections only in %.init.o files.
+
+config DO_NOT_FREE_INIT_MEMORY
+    bool
+    help
+      Prevent freeing of .init sections at the end of Xen boot.
+
 config CONDITION_COVERAGE
        bool "Condition coverage support"
        depends on COVERAGE && CC_HAS_MCDC
diff --git a/xen/Rules.mk b/xen/Rules.mk
index 24f447b95734..c884a4199dc2 100644
--- a/xen/Rules.mk
+++ b/xen/Rules.mk
@@ -145,10 +145,10 @@ endif
 $(call cc-option-add,cov-cflags-$(CONFIG_COVERAGE),CC,-fprofile-update=atomic)
 
 # Reset cov-cflags-y in cases where an objects has another one as prerequisite
-$(nocov-y) $(filter %.init.o, $(obj-y) $(obj-bin-y) $(extra-y)): \
+$(nocov-y) $(extra-y): \
     cov-cflags-y :=
 
-$(non-init-objects): _c_flags += $(cov-cflags-y)
+$(obj-y) $(obj-bin-y) $(extra-y) $(lib-y): _c_flags += $(cov-cflags-y)
 
 ifeq ($(CONFIG_UBSAN),y)
 # Any -fno-sanitize= options need to come after any -fsanitize= options
@@ -259,6 +259,7 @@ $(obj)/%.o: $(src)/%.S FORCE
 
 
 quiet_cmd_obj_init_o = INIT_O  $@
+ifneq ($(CONFIG_RELAX_INIT_CHECK),y)
 define cmd_obj_init_o
     $(OBJDUMP) -h $< | while read idx name sz rest; do \
         case "$$name" in \
@@ -271,6 +272,11 @@ define cmd_obj_init_o
     done || exit $$?; \
     $(OBJCOPY) $(foreach s,$(SPECIAL_DATA_SECTIONS),--rename-section 
.$(s)=.init.$(s)) $< $@
 endef
+else
+define cmd_obj_init_o
+    $(OBJCOPY) $(foreach s,$(SPECIAL_DATA_SECTIONS),--rename-section 
.$(s)=.init.$(s)) $< $@
+endef
+endif
 
 $(filter %.init.o,$(obj-y) $(obj-bin-y) $(extra-y)): $(obj)/%.init.o: 
$(obj)/%.o FORCE
        $(call if_changed,obj_init_o)
diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
index 22e929aac778..2a0b322445cd 100644
--- a/xen/arch/arm/setup.c
+++ b/xen/arch/arm/setup.c
@@ -69,10 +69,12 @@ static __used void noreturn init_done(void)
 {
     int rc;
 
+#ifndef CONFIG_DO_NOT_FREE_INIT_MEMORY
     /* Must be done past setting system_state. */
     unregister_init_virtual_region();
 
     free_init_memory();
+#endif
 
     /*
      * We have finished booting. Mark the section .data.ro_after_init
diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 7bbba76a92f8..280085c206a7 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -815,6 +815,7 @@ static void noreturn init_done(void)
     for ( unsigned int i = 0; i < bi->nr_domains; i++ )
         domain_unpause_by_systemcontroller(bi->domains[i].d);
 
+#ifndef CONFIG_DO_NOT_FREE_INIT_MEMORY
     /* MUST be done prior to removing .init data. */
     unregister_init_virtual_region();
 
@@ -837,6 +838,9 @@ static void noreturn init_done(void)
     destroy_xen_mappings(start, end);
     init_xenheap_pages(__pa(start), __pa(end));
     printk("Freed %lukB init memory\n", (end - start) >> 10);
+#else
+    (void) end, (void) start, (void)va;
+#endif
 
     /* Mark .rodata/ro_after_init as RO.  Maybe reform the superpage. */
     modify_xen_mappings((unsigned long)&__2M_rodata_start,
diff --git a/xen/common/libelf/Makefile b/xen/common/libelf/Makefile
index 917d12b006f7..60b3ae40728f 100644
--- a/xen/common/libelf/Makefile
+++ b/xen/common/libelf/Makefile
@@ -1,5 +1,4 @@
 obj-bin-y := libelf.o
-nocov-y += libelf.o
 libelf-objs := libelf-tools.o libelf-loader.o libelf-dominfo.o
 
 SECTIONS := text data $(SPECIAL_DATA_SECTIONS)
diff --git a/xen/common/libfdt/Makefile b/xen/common/libfdt/Makefile
index 6ce679f98f47..ae0f69c01373 100644
--- a/xen/common/libfdt/Makefile
+++ b/xen/common/libfdt/Makefile
@@ -5,7 +5,6 @@ SECTIONS := text data $(SPECIAL_DATA_SECTIONS)
 # For CONFIG_OVERLAY_DTB, libfdt functionalities will be needed during runtime.
 ifneq ($(CONFIG_OVERLAY_DTB),y)
 OBJCOPYFLAGS := $(foreach s,$(SECTIONS),--rename-section .$(s)=.init.$(s))
-nocov-y += libfdt.o
 endif
 
 obj-y += libfdt.o
-- 
2.34.1