[Xen-devel] [PATCH v3 07/17] livepatch/arm/x86: Strip note_depends symbol from test-cases.

[Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>]

This surfaced due to "xen/livepatch/x86/arm32: Force
.livepatch.depends section to be uint32_t aligned." which switched
to a different way of including the build-id.

Each livepatch ends with a global:

    30: 00000000     1 OBJECT  GLOBAL HIDDEN     7 note_depends

which will cause collision when loading.

One attempted solution was to add in the Makefile stanza:
 @sed -i '/unsigned/static unsinged/' $@

But that resulted in the note_depends being omitted from the livepatch
(as it was static and not used) which meant we would not have an
.livepatch_depends section which we require.

The solution to this is to remove the symbol via the --strip-symbols
after generating the livepatch.

However that fails as note_depends is in use by .rel.debug_info:
Relocation section '.rel.debug_info' at offset 0x151c contains 113 entries:
 Offset     Info    Type            Sym.Value  Sym. Name
..
00000625  00001e02 R_ARM_ABS32       00000000   note_depends

And the solution to that is to also slap on --strip-debug which removes
various .debug* sections (which livepatch ignores anyhow):
.debug_aranges, .debug_info, .debug_abbrev, .debug_line, .debug_frame,
.debug_str, and their .rel.* sections. And that will remove that.

Alternatively we could also use --localize-symbol so that note_depends
is not globally visible. But that won't help as hypervisor treats
both local and global symbols as global when resolving them.
(This is fixed in "livepatch: Add local and global symbol resolution."
but that patch is stuck in limbo).

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
v3: First version
---
 xen/test/livepatch/Makefile | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/xen/test/livepatch/Makefile b/xen/test/livepatch/Makefile
index 89ad89dfd5..9e73861732 100644
--- a/xen/test/livepatch/Makefile
+++ b/xen/test/livepatch/Makefile
@@ -53,6 +53,7 @@ xen_hello_world.o: config.h livepatch_depends.h
 .PHONY: $(LIVEPATCH)
 $(LIVEPATCH): xen_hello_world_func.o xen_hello_world.o
        $(LD) $(LDFLAGS) $(build_id_linker) -r -o $(LIVEPATCH) $^
+       $(OBJCOPY) --strip-debug --strip-symbol=$(NOTE_SYMBOL) $@
 
 #
 # This target is only accessible if CONFIG_LIVEPATCH is defined, which
@@ -88,18 +89,21 @@ xen_bye_world.o: config.h hello_world_livepatch_depends.h
 .PHONY: $(LIVEPATCH_BYE)
 $(LIVEPATCH_BYE): xen_bye_world_func.o xen_bye_world.o
        $(LD) $(LDFLAGS) $(build_id_linker) -r -o $(LIVEPATCH_BYE) $^
+       $(OBJCOPY) --strip-debug --strip-symbol=$(NOTE_SYMBOL) $@
 
 xen_replace_world.o: config.h livepatch_depends.h
 
 .PHONY: $(LIVEPATCH_REPLACE)
 $(LIVEPATCH_REPLACE): xen_replace_world_func.o xen_replace_world.o
        $(LD) $(LDFLAGS) $(build_id_linker) -r -o $(LIVEPATCH_REPLACE) $^
+       $(OBJCOPY) --strip-debug --strip-symbol=$(NOTE_SYMBOL) $@
 
 xen_nop.o: config.h livepatch_depends.h
 
 .PHONY: $(LIVEPATCH_NOP)
 $(LIVEPATCH_NOP): xen_nop.o
        $(LD) $(LDFLAGS) $(build_id_linker) -r -o $(LIVEPATCH_NOP) $^
+       $(OBJCOPY) --strip-debug --strip-symbol=$(NOTE_SYMBOL) $@
 
 .PHONY: livepatch
 livepatch: $(LIVEPATCH) $(LIVEPATCH_BYE) $(LIVEPATCH_REPLACE) $(LIVEPATCH_NOP)
-- 
2.13.3


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