If a symbol is not initialized, gcc declares it as a weak. It will be
resolved during the linking time.
Common symbols inside a library are fine, but we don't want them to be
resolved together with common symbols from another library.
For example:
lib/foo/main.c:
int some_variable;
int main(void) {
printf("libfoo: %p\n", some_variable);
}
lib/bar/main.c:
char some_variable;
int main(void) {
printf("libbar: %p\n", some_variable);
}
After linking the final Unikraft image, both libfoo and libbar will
get one address for their some_variable. Even if neither of them was
never declared "extern". Even if they have different types. Even if
some_variable is not listed in exportsyms.uk
The solution is to link library object files (libname.ld.o) with
'-d'. This will force linker to do allocation for common symbols.
Signed-off-by: Yuri Volchkov <yuri.volchkov@xxxxxxxxx>
---
Makefile.uk | 2 +-
lib/ukbus/exportsyms.uk | 1 +
2 files changed, 2 insertions(+), 1 deletion(-)
diff --git a/Makefile.uk b/Makefile.uk
index 0cc6690..289305a 100644
--- a/Makefile.uk
+++ b/Makefile.uk
@@ -20,7 +20,7 @@ CXXINCLUDES += -nostdinc -nostdlib -I$(CONFIG_UK_BASE)/include
# Set the text and data sections to be readable and writable. Also,
# do not page-align the data segment. If the output format supports
# Unix style magic numbers, mark the output as OMAGIC.
-LIBLDFLAGS += -nostdinc -nostdlib -Wl,--omagic -Wl,-r
+LIBLDFLAGS += -nostdinc -nostdlib -Wl,--omagic -Wl,-r -Wl,-d
LDFLAGS += -nostdinc -nostdlib -Wl,--omagic -Wl,--build-id=none
CFLAGS-$(CONFIG_OPTIMIZE_NONE) += -O0 -fno-optimize-sibling-calls -fno-tree-vectorize
diff --git a/lib/ukbus/exportsyms.uk b/lib/ukbus/exportsyms.uk
index db4476d..b202357 100644
--- a/lib/ukbus/exportsyms.uk
+++ b/lib/ukbus/exportsyms.uk
@@ -3,3 +3,4 @@ uk_bus_init
uk_bus_probe
_uk_bus_register
_uk_bus_unregister
+uk_bus_list
