powerpc/vdso: fix unnecessary rebuilds of vgettimeofday.o

vgettimeofday.o is unnecessarily rebuilt. Adding it to 'targets' is not
enough to fix the issue. Kbuild is correctly rebuilding it because the
command line is changed.

PowerPC builds each vdso directory twice; first in vdso_prepare to
generate vdso{32,64}-offsets.h, second as part of the ordinary build
process to embed vdso{32,64}.so.dbg into the kernel.

The problem shows up when CONFIG_PPC_WERROR=y due to the following line
in arch/powerpc/Kbuild:

  subdir-ccflags-$(CONFIG_PPC_WERROR) := -Werror

In the preparation stage, Kbuild directly visits the vdso directories,
hence it does not inherit subdir-ccflags-y. In the second descend,
Kbuild adds -Werror, which results in the command line flipping
with/without -Werror.

It implies a potential danger; if a more critical flag that would impact
the resulted vdso, the offsets recorded in the headers might be different
from real offsets in the embedded vdso images.

Removing the unneeded second descend solves the problem.

Reported-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/linuxppc-dev/87tuslxhry.fsf@mpe.ellerman.id.au/
Link: https://lore.kernel.org/r/20201223171142.707053-1-masahiroy@kernel.org

diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index fe2ef598e2ead0a5f429cd30a90e0edd48e22664..79ee7750937db06bade246afd710016a6fef2f1b 100644 (file)
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -51,7 +51,7 @@ obj-y                         += ptrace/
 obj-$(CONFIG_PPC64)            += setup_64.o \
                                   paca.o nvram_64.o note.o syscall_64.o
 obj-$(CONFIG_COMPAT)           += sys_ppc32.o signal_32.o
-obj-$(CONFIG_VDSO32)           += vdso32/
+obj-$(CONFIG_VDSO32)           += vdso32_wrapper.o
 obj-$(CONFIG_PPC_WATCHDOG)     += watchdog.o
 obj-$(CONFIG_HAVE_HW_BREAKPOINT)       += hw_breakpoint.o
 obj-$(CONFIG_PPC_DAWR)         += dawr.o
@@ -60,7 +60,7 @@ obj-$(CONFIG_PPC_BOOK3S_64)   += cpu_setup_power.o
 obj-$(CONFIG_PPC_BOOK3S_64)    += mce.o mce_power.o
 obj-$(CONFIG_PPC_BOOK3E_64)    += exceptions-64e.o idle_book3e.o
 obj-$(CONFIG_PPC_BARRIER_NOSPEC) += security.o
-obj-$(CONFIG_PPC64)            += vdso64/
+obj-$(CONFIG_PPC64)            += vdso64_wrapper.o
 obj-$(CONFIG_ALTIVEC)          += vecemu.o
 obj-$(CONFIG_PPC_BOOK3S_IDLE)  += idle_book3s.o
 procfs-y                       := proc_powerpc.o

diff --git a/arch/powerpc/kernel/vdso32/Makefile b/arch/powerpc/kernel/vdso32/Makefile
index 9cb6f524854b9d6f480e32f3cf346fe7d7a57071..7d9a6fee0e3dc1a01e066314721f09e732af8ae6 100644 (file)
--- a/arch/powerpc/kernel/vdso32/Makefile
+++ b/arch/powerpc/kernel/vdso32/Makefile
@@ -30,7 +30,7 @@ CC32FLAGS += -m32
 KBUILD_CFLAGS := $(filter-out -mcmodel=medium -mabi=elfv1 -mabi=elfv2 -mcall-aixdesc,$(KBUILD_CFLAGS))
 endif
 
-targets := $(obj-vdso32) vdso32.so.dbg
+targets := $(obj-vdso32) vdso32.so.dbg vgettimeofday.o
 obj-vdso32 := $(addprefix $(obj)/, $(obj-vdso32))
 
 GCOV_PROFILE := n
@@ -46,9 +46,6 @@ obj-y += vdso32_wrapper.o
 targets += vdso32.lds
 CPPFLAGS_vdso32.lds += -P -C -Upowerpc
 
-# Force dependency (incbin is bad)
-$(obj)/vdso32_wrapper.o : $(obj)/vdso32.so.dbg
-
 # link rule for the .so file, .lds has to be first
 $(obj)/vdso32.so.dbg: $(src)/vdso32.lds $(obj-vdso32) $(obj)/vgettimeofday.o FORCE
        $(call if_changed,vdso32ld_and_check)

diff --git a/arch/powerpc/kernel/vdso32/vdso32_wrapper.S b/arch/powerpc/kernel/vdso32/vdso32_wrapper.S
deleted file mode 100644 (file)
index 3f5ef03..0000000
--- a/arch/powerpc/kernel/vdso32/vdso32_wrapper.S
+++ /dev/null
@@ -1,14 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-#include <linux/linkage.h>
-#include <asm/page.h>
-
-       __PAGE_ALIGNED_DATA
-
-       .globl vdso32_start, vdso32_end
-       .balign PAGE_SIZE
-vdso32_start:
-       .incbin "arch/powerpc/kernel/vdso32/vdso32.so.dbg"
-       .balign PAGE_SIZE
-vdso32_end:
-
-       .previous

diff --git a/arch/powerpc/kernel/vdso32_wrapper.S b/arch/powerpc/kernel/vdso32_wrapper.S
new file mode 100644 (file)
index 0000000..3f5ef03
--- /dev/null
+++ b/arch/powerpc/kernel/vdso32_wrapper.S
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <linux/linkage.h>
+#include <asm/page.h>
+
+       __PAGE_ALIGNED_DATA
+
+       .globl vdso32_start, vdso32_end
+       .balign PAGE_SIZE
+vdso32_start:
+       .incbin "arch/powerpc/kernel/vdso32/vdso32.so.dbg"
+       .balign PAGE_SIZE
+vdso32_end:
+
+       .previous

diff --git a/arch/powerpc/kernel/vdso64/Makefile b/arch/powerpc/kernel/vdso64/Makefile
index bf363ff371521c65477853f89c8f4a16d3a0d3de..a06fb9b461fc776d08e0a9696756af4555fdb585 100644 (file)
--- a/arch/powerpc/kernel/vdso64/Makefile
+++ b/arch/powerpc/kernel/vdso64/Makefile
@@ -17,7 +17,7 @@ endif
 
 # Build rules
 
-targets := $(obj-vdso64) vdso64.so.dbg
+targets := $(obj-vdso64) vdso64.so.dbg vgettimeofday.o
 obj-vdso64 := $(addprefix $(obj)/, $(obj-vdso64))
 
 GCOV_PROFILE := n
@@ -29,15 +29,11 @@ ccflags-y := -shared -fno-common -fno-builtin -nostdlib \
        -Wl,-soname=linux-vdso64.so.1 -Wl,--hash-style=both
 asflags-y := -D__VDSO64__ -s
 
-obj-y += vdso64_wrapper.o
 targets += vdso64.lds
 CPPFLAGS_vdso64.lds += -P -C -U$(ARCH)
 
 $(obj)/vgettimeofday.o: %.o: %.c FORCE
 
-# Force dependency (incbin is bad)
-$(obj)/vdso64_wrapper.o : $(obj)/vdso64.so.dbg
-
 # link rule for the .so file, .lds has to be first
 $(obj)/vdso64.so.dbg: $(src)/vdso64.lds $(obj-vdso64) $(obj)/vgettimeofday.o FORCE
        $(call if_changed,vdso64ld_and_check)

diff --git a/arch/powerpc/kernel/vdso64/vdso64_wrapper.S b/arch/powerpc/kernel/vdso64/vdso64_wrapper.S
deleted file mode 100644 (file)
index 1d56d81..0000000
--- a/arch/powerpc/kernel/vdso64/vdso64_wrapper.S
+++ /dev/null
@@ -1,14 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-#include <linux/linkage.h>
-#include <asm/page.h>
-
-       __PAGE_ALIGNED_DATA
-
-       .globl vdso64_start, vdso64_end
-       .balign PAGE_SIZE
-vdso64_start:
-       .incbin "arch/powerpc/kernel/vdso64/vdso64.so.dbg"
-       .balign PAGE_SIZE
-vdso64_end:
-
-       .previous

diff --git a/arch/powerpc/kernel/vdso64_wrapper.S b/arch/powerpc/kernel/vdso64_wrapper.S
new file mode 100644 (file)
index 0000000..1d56d81
--- /dev/null
+++ b/arch/powerpc/kernel/vdso64_wrapper.S
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <linux/linkage.h>
+#include <asm/page.h>
+
+       __PAGE_ALIGNED_DATA
+
+       .globl vdso64_start, vdso64_end
+       .balign PAGE_SIZE
+vdso64_start:
+       .incbin "arch/powerpc/kernel/vdso64/vdso64.so.dbg"
+       .balign PAGE_SIZE
+vdso64_end:
+
+       .previous