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* [PATCH 1/2] powerpc/vdso: fix unnecessary rebuilds of vgettimeofday.o
@ 2020-12-23 17:11 Masahiro Yamada
  2020-12-23 17:11 ` [PATCH 2/2] powerpc/vdso64: remove meaningless vgettimeofday.o build rule Masahiro Yamada
                   ` (2 more replies)
  0 siblings, 3 replies; 7+ messages in thread
From: Masahiro Yamada @ 2020-12-23 17:11 UTC (permalink / raw)
  To: Michael Ellerman, Benjamin Herrenschmidt, Paul Mackerras,
	linuxppc-dev
  Cc: Ravi Bangoria, Masahiro Yamada, Nicholas Piggin, linux-kernel,
	Oliver O'Halloran, Greentime Hu, Michal Suchanek,
	Ard Biesheuvel, Daniel Axtens

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.

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

 arch/powerpc/kernel/Makefile                      | 4 ++--
 arch/powerpc/kernel/vdso32/Makefile               | 5 +----
 arch/powerpc/kernel/{vdso32 => }/vdso32_wrapper.S | 0
 arch/powerpc/kernel/vdso64/Makefile               | 6 +-----
 arch/powerpc/kernel/{vdso64 => }/vdso64_wrapper.S | 0
 5 files changed, 4 insertions(+), 11 deletions(-)
 rename arch/powerpc/kernel/{vdso32 => }/vdso32_wrapper.S (100%)
 rename arch/powerpc/kernel/{vdso64 => }/vdso64_wrapper.S (100%)

diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index fe2ef598e2ea..79ee7750937d 100644
--- 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 59aa2944ecae..42fc3de89b39 100644
--- a/arch/powerpc/kernel/vdso32/Makefile
+++ b/arch/powerpc/kernel/vdso32/Makefile
@@ -30,7 +30,7 @@ CC32FLAGS += -m32
 KBUILD_CFLAGS := $(filter-out -mcmodel=medium,$(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_wrapper.S
similarity index 100%
rename from arch/powerpc/kernel/vdso32/vdso32_wrapper.S
rename to arch/powerpc/kernel/vdso32_wrapper.S
diff --git a/arch/powerpc/kernel/vdso64/Makefile b/arch/powerpc/kernel/vdso64/Makefile
index d365810a689a..b50b39fedf74 100644
--- 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_wrapper.S
similarity index 100%
rename from arch/powerpc/kernel/vdso64/vdso64_wrapper.S
rename to arch/powerpc/kernel/vdso64_wrapper.S
-- 
2.27.0


^ permalink raw reply related	[flat|nested] 7+ messages in thread
end of thread, other threads:[~2021-03-31  9:03 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2020-12-23 17:11 [PATCH 1/2] powerpc/vdso: fix unnecessary rebuilds of vgettimeofday.o Masahiro Yamada
2020-12-23 17:11 ` [PATCH 2/2] powerpc/vdso64: remove meaningless vgettimeofday.o build rule Masahiro Yamada
2021-01-28  4:01   ` Masahiro Yamada
2021-01-28  4:01 ` [PATCH 1/2] powerpc/vdso: fix unnecessary rebuilds of vgettimeofday.o Masahiro Yamada
2021-01-29 11:41   ` Michael Ellerman
2021-03-31  9:03   ` Christophe Leroy
2021-02-03 11:46 ` Michael Ellerman

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