Messages in this thread | | | Date | Wed, 10 Jun 2020 11:32:19 +0100 | From | Will Deacon <> | Subject | Re: [PATCH v2] arm64: vdso32: add CONFIG_THUMB2_COMPAT_VDSO |
| |
On Wed, Jun 10, 2020 at 11:29:17AM +0100, Catalin Marinas wrote: > On Wed, Jun 10, 2020 at 09:47:55AM +0100, Will Deacon wrote: > > 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, > > On 32-bit, the vdso mode is a side-effect of how we build the kernel > image. I guess we haven't put much thought into whether we want to keep > the vdso in Thumb-2 or ARM mode.
I think your guess is correct!
> > 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. > > We could leave the config option in if we ever need to change the compat > vdso mode. But as not to confuse others with too many options, maybe > add: > > bool "Compile the vDSO in THUMB2 mode" if EXPERT > > Either way: > > Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Cheers, I'll add the dependency on EXPERT since I agree it's probably not something most people would want to touch. I'll also change the text to say "compat vDSO" not just vDSO.
Will
| |