Re: [PATCH v2 00/20] Introduce common headers

[Andy Lutomirski]

> On Mar 6, 2020, at 5:32 AM, Vincenzo Frascino <vincenzo.frascino@xxxxxxx> wrote:
> 
> ïBack 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 â__tag_setâ:
> ./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 â__tag_setâ:
> ./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/

I really like the approach, but Iâm wondering if âcommonâ is the right name. This directory is headers that arenât stable ABI like uapi but are shared between the kernel and the vDSO. Regular user code should *not* include these, right?

Would âvdsoâ or perhaps âprivate-abiâ be clearer?

>  * 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@xxxxxxxxxxxxxxxxxxxx
> [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@xxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Russell King <linux@xxxxxxxxxxxxxxx>
> Cc: Paul Burton <paul.burton@xxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Stephen Boyd <sboyd@xxxxxxxxxx>
> Cc: Mark Salyzyn <salyzyn@xxxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Peter Collingbourne <pcc@xxxxxxxxxx>
> Cc: Dmitry Safonov <0x7f454c46@xxxxxxxxx>
> Cc: Andrei Vagin <avagin@xxxxxxxxxx>
> Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
> 
> 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
>