From e564ee0c20100a1064bbdead1a4d674f916721b7 Mon Sep 17 00:00:00 2001 From: David Matlack Date: Fri, 20 May 2022 23:32:46 +0000 Subject: [PATCH] KVM: selftests: Link selftests directly with lib object files The linker does obey strong/weak symbols when linking static libraries, it simply resolves an undefined symbol to the first-encountered symbol. This means that defining __weak arch-generic functions and then defining arch-specific strong functions to override them in libkvm will not always work. More specifically, if we have: lib/generic.c: void __weak foo(void) { pr_info("weak\n"); } void bar(void) { foo(); } lib/x86_64/arch.c: void foo(void) { pr_info("strong\n"); } And a selftest that calls bar(), it will print "weak". Now if you make generic.o explicitly depend on arch.o (e.g. add function to arch.c that is called directly from generic.c) it will print "strong". In other words, it seems that the linker is free to throw out arch.o when linking because generic.o does not explicitly depend on it, which causes the linker to lose the strong symbol. One solution is to link libkvm.a with --whole-archive so that the linker doesn't throw away object files it thinks are unnecessary. However that is a bit difficult to plumb since we are using the common selftests makefile rules. An easier solution is to drop libkvm.a just link selftests with all the .o files that were originally in libkvm.a. Reviewed-by: Peter Xu Signed-off-by: David Matlack Message-Id: <20220520233249.3776001-9-dmatlack@google.com> Signed-off-by: Paolo Bonzini --- tools/testing/selftests/kvm/Makefile | 11 ++++------- 1 file changed, 4 insertions(+), 7 deletions(-) diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile index e7d65e04b16a9..804bf927618a1 100644 --- a/tools/testing/selftests/kvm/Makefile +++ b/tools/testing/selftests/kvm/Makefile @@ -173,12 +173,13 @@ LDFLAGS += -pthread $(no-pie-option) $(pgste-option) # $(TEST_GEN_PROGS) starts with $(OUTPUT)/ include ../lib.mk -STATIC_LIBS := $(OUTPUT)/libkvm.a LIBKVM_C := $(filter %.c,$(LIBKVM)) LIBKVM_S := $(filter %.S,$(LIBKVM)) LIBKVM_C_OBJ := $(patsubst %.c, $(OUTPUT)/%.o, $(LIBKVM_C)) LIBKVM_S_OBJ := $(patsubst %.S, $(OUTPUT)/%.o, $(LIBKVM_S)) -EXTRA_CLEAN += $(LIBKVM_C_OBJ) $(LIBKVM_S_OBJ) $(STATIC_LIBS) cscope.* +LIBKVM_OBJS = $(LIBKVM_C_OBJ) $(LIBKVM_S_OBJ) + +EXTRA_CLEAN += $(LIBKVM_OBJS) cscope.* x := $(shell mkdir -p $(sort $(dir $(LIBKVM_C_OBJ) $(LIBKVM_S_OBJ)))) $(LIBKVM_C_OBJ): $(OUTPUT)/%.o: %.c @@ -187,12 +188,8 @@ $(LIBKVM_C_OBJ): $(OUTPUT)/%.o: %.c $(LIBKVM_S_OBJ): $(OUTPUT)/%.o: %.S $(CC) $(CFLAGS) $(CPPFLAGS) $(TARGET_ARCH) -c $< -o $@ -LIBKVM_OBJS = $(LIBKVM_C_OBJ) $(LIBKVM_S_OBJ) -$(OUTPUT)/libkvm.a: $(LIBKVM_OBJS) - $(AR) crs $@ $^ - x := $(shell mkdir -p $(sort $(dir $(TEST_GEN_PROGS)))) -$(TEST_GEN_PROGS): $(STATIC_LIBS) +$(TEST_GEN_PROGS): $(LIBKVM_OBJS) cscope: include_paths = $(LINUX_TOOL_INCLUDE) $(LINUX_HDR_PATH) include lib .. cscope: -- 2.39.5