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Subject[PATCH] x86/vdso: drop implicit common-page-size linker flag
From
These are implied by the target architecture and for x86_64 match the
max-page-size. The default for non-NaCl x86_64 is 0x1000 (4096).

In bfd the common page size is defined as 0x1000 (4096) for non-NaCl
x86_64 targets:

bfd/elf64-x86-64.c:
4998:#define ELF_COMMONPAGESIZE 0x1000

For gold, the common page size is defined as 0x1000 (4096) for non-NaCl
x86_64 targets:

gold/x86_64.cc:
1413: 0x1000, // common_pagesize (overridable by -z common-page-size)
1442: 0x1000, // common_pagesize (overridable by -z common-page-size)

(ELF_COMMONPAGESIZE also defaults to ELF_MAXPAGESIZE when not set
explicitly for a target architecture in bfd/elfxx-target.h, but that's
not relevant for x86_64).

Because it's implied by the target architecture, it's of questionable
use to implement in LLD. This patch resolves one of the issues towards
using LLD to link an x86_64 kernel.

Fixes commit 2aae950b21e4 ("x86_64: Add vDSO for x86-64 with
gettimeofday/clock_gettime/getcpu")

Link: https://bugs.llvm.org/show_bug.cgi?id=38774
Link: https://github.com/ClangBuiltLinux/linux/issues/31
Cc: Fangrui Song <maskray@google.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Reported-by: Dmitry Golovin <dima@golovin.in>
Reported-by: Bill Wendling <morbo@google.com>
Suggested-by: Dmitry Golovin <dima@golovin.in>
Suggested-by: Rui Ueyama <ruiu@google.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
arch/x86/entry/vdso/Makefile | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
index 141d415a8c80..0624bf2266fd 100644
--- a/arch/x86/entry/vdso/Makefile
+++ b/arch/x86/entry/vdso/Makefile
@@ -47,7 +47,7 @@ targets += $(vdso_img_sodbg) $(vdso_img-y:%=vdso%.so)
CPPFLAGS_vdso.lds += -P -C

VDSO_LDFLAGS_vdso.lds = -m elf_x86_64 -soname linux-vdso.so.1 --no-undefined \
- -z max-page-size=4096 -z common-page-size=4096
+ -z max-page-size=4096

$(obj)/vdso64.so.dbg: $(obj)/vdso.lds $(vobjs) FORCE
$(call if_changed,vdso)
@@ -98,7 +98,7 @@ CFLAGS_REMOVE_vvar.o = -pg

CPPFLAGS_vdsox32.lds = $(CPPFLAGS_vdso.lds)
VDSO_LDFLAGS_vdsox32.lds = -m elf32_x86_64 -soname linux-vdso.so.1 \
- -z max-page-size=4096 -z common-page-size=4096
+ -z max-page-size=4096

# x32-rebranded versions
vobjx32s-y := $(vobjs-y:.o=-x32.o)
--
2.20.0.rc1.387.gf8505762e3-goog
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