linux-kernel - [PATCH 0/6] Don't use BIT() macro in UAPI headers

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Date:   Thu, 20 May 2021 03:43:37 -0700
From:   Joe Richey <joerichey94@...il.com>
To:     trivial@...nel.org
Cc:     Joe Richey <joerichey@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Zhangfei Gao <zhangfei.gao@...aro.org>,
        Zhou Wang <wangzhou1@...ilicon.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-media@...r.kernel.org,
        linux-accelerators@...ts.ozlabs.org
Subject: [PATCH 0/6] Don't use BIT() macro in UAPI headers

From: Joe Richey <joerichey@...gle.com>

The BIT(n) macro is used in the kernel as an alias for (1 << n).
However, it is not defined in the UAPI headers, which means that any
UAPI header files must be careful not to use it, or else the user
will get a linker error. For example, compiling the following program:

    #include <sys/auxv.h>
    #include <asm/hwcap2.h>

    // Detect if FSGSBASE instructions are enabled
    int main() {
        unsigned long val = getauxval(AT_HWCAP2);
        return !(val & HWCAP2_FSGSBASE);
    }

Results in the following likner error:

    /usr/bin/ld: /tmp/cceFpAdR.o: in function `main':
    gs.c:(.text+0x21): undefined reference to `BIT'

This patch series changes all UAPI uses of BIT() to just be open-coded.
However, there really should be a check for this in checkpatch.pl
Currently, the script actually _encourages_ users to use the BIT macro
even if adding things to UAPI.

Running `rg "BIT\(" **/uapi/**` shows no more usage of BIT() in any
UAPI headers. Tested by building a basic kernel. Changes are trivial.

Joe Richey (6):
  x86/elf: Don't use BIT() macro in UAPI headers
  KVM: X86: Don't use BIT() macro in UAPI headers
  drivers: firmware: psci: Don't use BIT() macro in UAPI headers
  uacce: Don't use BIT() macro in UAPI headers
  media: vicodec: Don't use BIT() macro in UAPI headers
  tools headers UAPI: Sync pkt_sched.h with the kernel sources

 arch/x86/include/uapi/asm/hwcap2.h   |   2 +-
 include/uapi/linux/kvm.h             |   4 +-
 include/uapi/linux/psci.h            |   2 +-
 include/uapi/linux/v4l2-controls.h   |  22 ++---
 include/uapi/misc/uacce/uacce.h      |   2 +-
 tools/include/uapi/linux/kvm.h       |   4 +-
 tools/include/uapi/linux/pkt_sched.h | 122 ++++++++++++++++++++++++---
 7 files changed, 130 insertions(+), 28 deletions(-)

-- 
2.31.1