linux-kernel - [PATCH 1/2] powerpc/vdso64: link vdso64 with linker

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Date:   Tue,  1 Sep 2020 15:25:22 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Christophe Leroy <christophe.leroy@....fr>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Kees Cook <keescook@...omium.org>,
        Fangrui Song <maskray@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: [PATCH 1/2] powerpc/vdso64: link vdso64 with linker

Rather than invoke the compiler as the driver, use the linker. That way
we can check --orphan-handling=warn support correctly, as cc-ldoption
was removed in
commit 055efab3120b ("kbuild: drop support for cc-ldoption").

Painstakingly compared the output between `objdump -a` before and after
this change. Now function symbols have the correct type of FUNC rather
than NONE, and the entry is slightly different (which doesn't matter for
the vdso). Binary size is the same.

Fixes: commit f2af201002a8 ("powerpc/build: vdso linker warning for orphan sections")
Link: https://lore.kernel.org/lkml/CAKwvOdnn3wxYdJomvnveyD_njwRku3fABWT_bS92duihhywLJQ@mail.gmail.com/
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
 arch/powerpc/include/asm/vdso.h         | 17 ++---------------
 arch/powerpc/kernel/vdso64/Makefile     |  8 ++++++--
 arch/powerpc/kernel/vdso64/vdso64.lds.S |  1 -
 3 files changed, 8 insertions(+), 18 deletions(-)

diff --git a/arch/powerpc/include/asm/vdso.h b/arch/powerpc/include/asm/vdso.h
index 2ff884853f97..11b2ecf49f79 100644
--- a/arch/powerpc/include/asm/vdso.h
+++ b/arch/powerpc/include/asm/vdso.h
@@ -24,19 +24,7 @@ int vdso_getcpu_init(void);
 
 #else /* __ASSEMBLY__ */
 
-#ifdef __VDSO64__
-#define V_FUNCTION_BEGIN(name)		\
-	.globl name;			\
-	name:				\
-
-#define V_FUNCTION_END(name)		\
-	.size name,.-name;
-
-#define V_LOCAL_FUNC(name) (name)
-#endif /* __VDSO64__ */
-
-#ifdef __VDSO32__
-
+#if defined(__VDSO32__) || defined (__VDSO64__)
 #define V_FUNCTION_BEGIN(name)		\
 	.globl name;			\
 	.type name,@function; 		\
@@ -46,8 +34,7 @@ int vdso_getcpu_init(void);
 	.size name,.-name;
 
 #define V_LOCAL_FUNC(name) (name)
-
-#endif /* __VDSO32__ */
+#endif /* __VDSO{32|64}__ */
 
 #endif /* __ASSEMBLY__ */
 
diff --git a/arch/powerpc/kernel/vdso64/Makefile b/arch/powerpc/kernel/vdso64/Makefile
index 38c317f25141..7ea3ce537d0a 100644
--- a/arch/powerpc/kernel/vdso64/Makefile
+++ b/arch/powerpc/kernel/vdso64/Makefile
@@ -32,9 +32,13 @@ $(obj)/%.so: OBJCOPYFLAGS := -S
 $(obj)/%.so: $(obj)/%.so.dbg FORCE
 	$(call if_changed,objcopy)
 
+ldflags-y := -shared -soname linux-vdso64.so.1 \
+	$(call ld-option, --eh-frame-hdr) \
+	$(call ld-option, --orphan-handling=warn) -T
+
 # actual build commands
-quiet_cmd_vdso64ld = VDSO64L $@
-      cmd_vdso64ld = $(CC) $(c_flags) -o $@ -Wl,-T$(filter %.lds,$^) $(filter %.o,$^) $(call cc-ldoption, -Wl$(comma)--orphan-handling=warn)
+quiet_cmd_vdso64ld = LD      $@
+      cmd_vdso64ld = $(cmd_ld)
 
 # install commands for the unstripped file
 quiet_cmd_vdso_install = INSTALL $@
diff --git a/arch/powerpc/kernel/vdso64/vdso64.lds.S b/arch/powerpc/kernel/vdso64/vdso64.lds.S
index 4e3a8d4ee614..58c33b704b6a 100644
--- a/arch/powerpc/kernel/vdso64/vdso64.lds.S
+++ b/arch/powerpc/kernel/vdso64/vdso64.lds.S
@@ -11,7 +11,6 @@ OUTPUT_FORMAT("elf64-powerpcle", "elf64-powerpcle", "elf64-powerpcle")
 OUTPUT_FORMAT("elf64-powerpc", "elf64-powerpc", "elf64-powerpc")
 #endif
 OUTPUT_ARCH(powerpc:common64)
-ENTRY(_start)
 
 SECTIONS
 {
-- 
2.28.0.402.g5ffc5be6b7-goog