[PATCH v2 00/20] Introduce common headers

Vincenzo Frascino
2020-03-06T13:32:54Z

Back in July last year we started having a problem in building compat
vDSOs on arm64 [1] [2] that was not present when the arm64 porting to
the Unified vDSO was done. In particular when the compat vDSO on such
architecture is built with gcc it generates the warning below:

In file included from ./arch/arm64/include/asm/thread_info.h:17:0,
from ./include/linux/thread_info.h:38,
from ./arch/arm64/include/asm/preempt.h:5,
from ./include/linux/preempt.h:78,
from ./include/linux/spinlock.h:51,
from ./include/linux/seqlock.h:36,
from ./include/linux/time.h:6,
from ./lib/vdso/gettimeofday.c:7,
from <command-line>:0:
./arch/arm64/include/asm/memory.h: In function ‘__tag_set’:
./arch/arm64/include/asm/memory.h:233:15: warning: cast from pointer
to integer of different size [-Wpointer-to-int-cast]
u64 __addr = (u64)addr & ~__tag_shifted(0xff);
^
In file included from ./arch/arm64/include/asm/pgtable-hwdef.h:8:0,
from ./arch/arm64/include/asm/processor.h:34,
from ./arch/arm64/include/asm/elf.h:118,
from ./include/linux/elf.h:5,
from ./include/linux/elfnote.h:62,
from arch/arm64/kernel/vdso32/note.c:11:
./arch/arm64/include/asm/memory.h: In function ‘__tag_set’:
./arch/arm64/include/asm/memory.h:233:15: warning: cast from pointer
to integer of different size [-Wpointer-to-int-cast]
u64 __addr = (u64)addr & ~__tag_shifted(0xff);

The same porting does not build at all when the selected compiler is
clang.

I started an investigation to try to understand better the problem and
after various discussions at Plumbers and Recipes last year the
conclusion was that the vDSO library as it stands it is including more
headers that it needs. In particular, being a user-space library, it
should require only the UAPI and a minimal vDSO kernel interface instead
of all the kernel-related inline functions which are not directly used
and in some cases can have side effects.

To solve the problem, I decided to use the approach below:
* Extract from include/linux/ the vDSO required kernel interface
and place it in include/common/
* Make sure that where meaningful the kernel includes "common"
* Limit the vDSO library to include headers coming only from UAPI
and "common" (with 2 exceptions compiler.h for barriers and
param.h for HZ).
* Adapt all the architectures that support the unified vDSO library
to use "common" headers.

According to me this approach allows up to exercise a better control on
what the vDSO library can include and to prevent potential issues in
future.

This patch series contains the implementation of the described approach.

The "common" headers have been verified on all the architectures that support
unified vDSO using the vdsotest [3] testsuite for what concerns the vDSO part
and randconfig to verify that they are included in the correct places.

To simplify the testing, a copy of the patchset on top of a recent linux
tree can be found at [4].

[1] https://github.com/ClangBuiltLinux/linux/issues/595
[2] https://lore.kernel.org/lkml/20190926151704.GH9689@arrakis.emea.arm.com
[3] https://github.com/nathanlynch/vdsotest
[4] git://linux-arm.org/linux-vf.git common-headers/v2

Changes:
--------
v2:
- Addressed review comments for clang support.
- Rebased on 5.6-rc4.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Paul Burton <paul.burton@mips.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: Mark Salyzyn <salyzyn@android.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: Andrei Vagin <avagin@openvz.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>

Vincenzo Frascino (20):
linux/const.h: Extract common header for vDSO
linux/bits.h: Extract common header for vDSO
linux/limits.h: Extract common header for vDSO
linux/math64.h: Extract common header for vDSO
linux/time.h: Extract common header for vDSO
linux/time32.h: Extract common header for vDSO
linux/time64.h: Extract common header for vDSO
linux/jiffies.h: Extract common header for vDSO
linux/ktime.h: Extract common header for vDSO
common: Introduce processor.h
linux/elfnote.h: Replace elf.h with UAPI equivalent
arm64: Introduce asm/common/processor.h
arm64: vdso: Include common headers in the vdso library
arm64: vdso32: Include common headers in the vdso library
arm64: Introduce asm/common/arch_timer.h
mips: vdso: Enable mips to use common headers
x86: vdso: Enable x86 to use common headers
arm: vdso: Enable arm to use common headers
lib: vdso: Enable common headers
arm64: vdso32: Enable Clang Compilation

arch/arm/include/asm/common/cp15.h | 38 +++++++++++++++++++
arch/arm/include/asm/common/processor.h | 22 +++++++++++
arch/arm/include/asm/cp15.h | 20 +---------
arch/arm/include/asm/processor.h | 11 +-----
arch/arm/include/asm/vdso/gettimeofday.h | 4 +-
arch/arm64/include/asm/arch_timer.h | 29 +++-----------
arch/arm64/include/asm/common/arch_timer.h | 33 ++++++++++++++++
arch/arm64/include/asm/common/processor.h | 31 +++++++++++++++
arch/arm64/include/asm/processor.h | 16 +-------
.../include/asm/vdso/compat_gettimeofday.h | 2 +-
arch/arm64/include/asm/vdso/gettimeofday.h | 8 ++--
arch/arm64/kernel/vdso/vgettimeofday.c | 2 -
arch/arm64/kernel/vdso32/Makefile | 13 ++++++-
arch/arm64/kernel/vdso32/vgettimeofday.c | 3 --
arch/mips/include/asm/common/processor.h | 27 +++++++++++++
arch/mips/include/asm/processor.h | 16 +-------
arch/mips/include/asm/vdso/gettimeofday.h | 4 --
arch/x86/include/asm/common/processor.h | 23 +++++++++++
arch/x86/include/asm/processor.h | 12 +-----
include/common/bits.h | 9 +++++
include/common/const.h | 10 +++++
include/common/jiffies.h | 11 ++++++
include/common/ktime.h | 16 ++++++++
include/common/limits.h | 18 +++++++++
include/common/math64.h | 24 ++++++++++++
include/common/processor.h | 14 +++++++
include/common/time.h | 12 ++++++
include/common/time32.h | 17 +++++++++
include/common/time64.h | 14 +++++++
include/linux/bits.h | 2 +-
include/linux/const.h | 5 +--
include/linux/elfnote.h | 2 +-
include/linux/jiffies.h | 4 +-
include/linux/ktime.h | 9 +----
include/linux/limits.h | 13 +------
include/linux/math64.h | 20 +---------
include/linux/time.h | 5 +--
include/linux/time32.h | 13 +------
include/linux/time64.h | 10 +----
include/vdso/datapage.h | 32 ++++++++++++++--
lib/vdso/gettimeofday.c | 21 ----------
41 files changed, 388 insertions(+), 207 deletions(-)
create mode 100644 arch/arm/include/asm/common/cp15.h
create mode 100644 arch/arm/include/asm/common/processor.h
create mode 100644 arch/arm64/include/asm/common/arch_timer.h
create mode 100644 arch/arm64/include/asm/common/processor.h
create mode 100644 arch/mips/include/asm/common/processor.h
create mode 100644 arch/x86/include/asm/common/processor.h
create mode 100644 include/common/bits.h
create mode 100644 include/common/const.h
create mode 100644 include/common/jiffies.h
create mode 100644 include/common/ktime.h
create mode 100644 include/common/limits.h
create mode 100644 include/common/math64.h
create mode 100644 include/common/processor.h
create mode 100644 include/common/time.h
create mode 100644 include/common/time32.h
create mode 100644 include/common/time64.h

--
2.25.1