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    SubjectRe: [PATCH] arm64: Fix off-by-one vdso trampoline return value
    On Wed, Nov 11, 2020 at 4:14 PM Will McVicker <willmcvicker@google.com> wrote:
    >
    > Depending on your host nm version, the generated header
    > `include/generated/vdso32-offsets.h` may have the bottom bit set for the
    > thumb vdso offset addresses (as observed when using llvm-nm). This

    Sorry, the commit message seems to imply a bug in llvm-nm, but I don't
    think that's the case. If it is, please, send us a bugreport.

    $ aarch64-linux-gnu-nm arch/arm64/kernel/vdso32/vdso.so.raw | grep thumb
    00000968 T __kernel_rt_sigreturn_thumb
    00000960 T __kernel_sigreturn_thumb
    00000968 t VDSO_compat_rt_sigreturn_thumb
    00000960 t VDSO_compat_sigreturn_thumb
    $ llvm-nm arch/arm64/kernel/vdso32/vdso.so.raw | grep thumb
    00000968 t VDSO_compat_rt_sigreturn_thumb
    00000960 t VDSO_compat_sigreturn_thumb
    00000968 T __kernel_rt_sigreturn_thumb
    00000960 T __kernel_sigreturn_thumb
    $ /usr/bin/nm arch/arm64/kernel/vdso32/vdso.so.raw | grep thumb
    00000969 T __kernel_rt_sigreturn_thumb
    00000961 T __kernel_sigreturn_thumb
    00000969 t VDSO_compat_rt_sigreturn_thumb
    00000961 t VDSO_compat_sigreturn_thumb
    $ /usr/bin/nm --version
    GNU nm (GNU Binutils for Debian) 2.35.1

    Would you mind amending the commit message to not imply that llvm-nm is broken?

    It might be of interest to find out why the host `nm` was invoked,
    rather than $(NM)/$(CROSS_COMPILE)nm.

    > results in an additional +1 for thumb vdso trampoline return values
    > since compat_setup_return() already includes `vdso_trampoline + thumb`.
    > As a result, I see a SIGBUS error when running the LTP test
    > syscalls.rt_sigaction01. To fix this, let's clear the bottom bit of the
    > vdso_offset in the VDSO_SYMBOL macro.
    >
    > Test: LTP test syscalls.rt_sigaction01
    > Fixes: f01703b3d2e6 ("arm64: compat: Get sigreturn trampolines from vDSO")
    > Signed-off-by: Will McVicker <willmcvicker@google.com>
    > ---
    > arch/arm64/include/asm/vdso.h | 2 +-
    > 1 file changed, 1 insertion(+), 1 deletion(-)
    >
    > diff --git a/arch/arm64/include/asm/vdso.h b/arch/arm64/include/asm/vdso.h
    > index f99dcb94b438..a7384379e8e1 100644
    > --- a/arch/arm64/include/asm/vdso.h
    > +++ b/arch/arm64/include/asm/vdso.h
    > @@ -23,7 +23,7 @@
    >
    > #define VDSO_SYMBOL(base, name) \
    > ({ \
    > - (void *)(vdso_offset_##name - VDSO_LBASE + (unsigned long)(base)); \
    > + (void *)((vdso_offset_##name & ~1UL) - VDSO_LBASE + (unsigned long)(base)); \
    > })
    >
    > #endif /* !__ASSEMBLY__ */
    > --
    > 2.29.2.299.gdc1121823c-goog
    >


    --
    Thanks,
    ~Nick Desaulniers

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