[PATCH] livepatch: set -f{function,data}-sections compiler option

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

If livepatching support is enabled build the hypervisor with
-f{function,data}-sections compiler options, which is required by the
livepatching tools to detect changes and create livepatches.

This shouldn't result in any functional change on the hypervisor
binary image, but does however require some changes in the linker
script in order to handle that each function and data item will now be
placed into its own section in object files. As a result add catch-all
for .text, .data and .bss in order to merge each individual item
section into the final image.

The main difference will be that .text.startup will end up being part
of .text rather than .init, and thus won't be freed. Such section only
seems to appear when using -Os, which not the default for debug or
production binaries.

The benefit of having CONFIG_LIVEPATCH enable those compiler options
is that the livepatch build tools no longer need to fiddle with the
build system in order to enable them. Note the current livepatch tools
are broken after the recent build changes due to the way they
attempt to set  -f{function,data}-sections.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/Makefile           | 4 ++++
 xen/arch/arm/xen.lds.S | 9 +++++++++
 xen/arch/x86/xen.lds.S | 9 +++++++++
 xen/common/Kconfig     | 4 +++-
 4 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/xen/Makefile b/xen/Makefile
index ed4891daf1..bf14a9bdd2 100644
--- a/xen/Makefile
+++ b/xen/Makefile
@@ -269,6 +269,10 @@ else
 CFLAGS += -fomit-frame-pointer
 endif
 
+ifeq ($(CONFIG_LIVEPATCH),y)
+CFLAGS += -ffunction-sections -fdata-sections
+endif
+
 CFLAGS += -nostdinc -fno-builtin -fno-common
 CFLAGS += -Werror -Wredundant-decls -Wno-pointer-arith
 $(call cc-option-add,CFLAGS,CC,-Wvla)
diff --git a/xen/arch/arm/xen.lds.S b/xen/arch/arm/xen.lds.S
index 08016948ab..1c7c7d5469 100644
--- a/xen/arch/arm/xen.lds.S
+++ b/xen/arch/arm/xen.lds.S
@@ -33,6 +33,9 @@ SECTIONS
        *(.text)
        *(.text.cold)
        *(.text.unlikely)
+#ifdef CONFIG_LIVEPATCH
+       *(.text.*)
+#endif
        *(.fixup)
        *(.gnu.warning)
        _etext = .;             /* End of text section */
@@ -96,6 +99,9 @@ SECTIONS
 
        *(.data.rel)
        *(.data.rel.*)
+#ifdef CONFIG_LIVEPATCH
+       *(.data.*)
+#endif
        CONSTRUCTORS
   } :text
 
@@ -208,6 +214,9 @@ SECTIONS
        . = ALIGN(SMP_CACHE_BYTES);
        __per_cpu_data_end = .;
        *(.bss)
+#ifdef CONFIG_LIVEPATCH
+       *(.bss.*)
+#endif
        . = ALIGN(POINTER_ALIGN);
        __bss_end = .;
   } :text
diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
index 83def6541e..81bb608151 100644
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -88,6 +88,9 @@ SECTIONS
 
        *(.text.cold)
        *(.text.unlikely)
+#ifdef CONFIG_LIVEPATCH
+       *(.text.*)
+#endif
        *(.fixup)
        *(.gnu.warning)
        _etext = .;             /* End of text section */
@@ -292,6 +295,9 @@ SECTIONS
        *(.data)
        *(.data.rel)
        *(.data.rel.*)
+#ifdef CONFIG_LIVEPATCH
+       *(.data.*)
+#endif
        CONSTRUCTORS
   } PHDR(text)
 
@@ -308,6 +314,9 @@ SECTIONS
        . = ALIGN(SMP_CACHE_BYTES);
        __per_cpu_data_end = .;
        *(.bss)
+#ifdef CONFIG_LIVEPATCH
+       *(.bss.*)
+#endif
        . = ALIGN(POINTER_ALIGN);
        __bss_end = .;
   } PHDR(text)
diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index 6443943889..2423d9f490 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -353,7 +353,9 @@ config CRYPTO
 config LIVEPATCH
        bool "Live patching support"
        default X86
-       depends on "$(XEN_HAS_BUILD_ID)" = "y"
+       depends on "$(XEN_HAS_BUILD_ID)" = "y" && \
+                  $(cc-option,-ffunction-sections) && \
+                  $(cc-option,-fdata-sections)
        ---help---
          Allows a running Xen hypervisor to be dynamically patched using
          binary patches without rebooting. This is primarily used to binarily
-- 
2.34.1