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    SubjectRe: [PATCH v2] arm64: vdso32: add CONFIG_THUMB2_COMPAT_VDSO
    On Tue, Jun 09, 2020 at 04:55:13PM -0700, Nick Desaulniers wrote:
    > On Tue, Jun 9, 2020 at 1:35 PM Catalin Marinas <catalin.marinas@arm.com> wrote:
    > >
    > > On Mon, Jun 08, 2020 at 01:57:08PM -0700, Nick Desaulniers wrote:
    > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
    > > > index 7f9d38444d6d..fe9e6b231cac 100644
    > > > --- a/arch/arm64/Kconfig
    > > > +++ b/arch/arm64/Kconfig
    > > > @@ -1299,6 +1299,14 @@ config COMPAT_VDSO
    > > > You must have a 32-bit build of glibc 2.22 or later for programs
    > > > to seamlessly take advantage of this.
    > > >
    > > > +config THUMB2_COMPAT_VDSO
    > > > + bool "Compile the vDSO in THUMB2 mode"
    > > > + depends on COMPAT_VDSO
    > > > + default y
    > > > + help
    > > > + Compile the compat vDSO with -mthumb -fomit-frame-pointer if y, otherwise
    > > > + as -marm.
    > >
    > > Now that we understood the issue (I think), do we actually need this
    > > choice? Why not going for -mthumb -fomit-frame-pointer always for the
    > > compat vdso?
    >
    > "Why should the compat vdso be configurable?" is a fair question. I
    > don't have an answer, but maybe some of the folks on thread do?
    >
    > Our problem is more so "if the vdso is built as thumb, we need it also
    > explicitly built with -fomit-frame-pointer." Whether it should be
    > built as thumb, arm, or configurable (and which default to pick in
    > that case) are still an open questions. Will asked for it to be
    > configurable, so I sent a patch making it configurable.

    It's configurable for 32-bit arm, so I was just following that as it's
    hardly a maintenance burden to support both. I suppose you could have
    a toolchain that only supports one or the other, but it does seem a little
    esoteric if you're building a kernel for an arm64 CPU.

    Will

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