[Xen-devel] [PATCH v4 08/11] livepatch/arm/x86: Rename 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.

One solution 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 patch decides to pick an easier path, just rename the symbol
by prefixing it with the name of the livepatch:

$ nm *.livepatch | grep depend
0000000000000000 R xen_bye_world.livepatch_note_depends
0000000000000000 R xen_hello_world.livepatch_note_depends
0000000000000000 R xen_local_symbols.livepatch_note_depends
0000000000000000 R xen_nop.livepatch_note_depends
0000000000000000 R xen_replace_world.livepatch_note_depends

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
Cc: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>

v3: First posting.
v4: Instead of stripping the symbol (and also using --strip-debug),
    just rename the symbol.
---
 xen/test/livepatch/Makefile | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/xen/test/livepatch/Makefile b/xen/test/livepatch/Makefile
index d23833e36f..b48669cc13 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) --redefine-sym $(NOTE_SYMBOL)=$@_$(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) --redefine-sym $(NOTE_SYMBOL)=$@_$(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) --redefine-sym $(NOTE_SYMBOL)=$@_$(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) --redefine-sym $(NOTE_SYMBOL)=$@_$(NOTE_SYMBOL) $@
 
 .PHONY: livepatch
 livepatch: $(LIVEPATCH) $(LIVEPATCH_BYE) $(LIVEPATCH_REPLACE) $(LIVEPATCH_NOP)
-- 
2.13.3


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