On Mon, 2018-04-02 at 15:27 +0200, Adam Borowski wrote: > On Sun, Apr 01, 2018 at 11:24:14AM +0800, Paul Wise wrote: > > CCing the maintainer of arch-test who will probably have some input. > > > > On Sun, 2018-04-01 at 11:32 +0900, Hideki Yamane wrote: > > > > > + if [ "$HOST_ARCH" = "amd64" ] && [ "$ARCH" = "i386" ] ; then > > > + # i386 binary can be run on amd64 host > > > > It is a bad idea to hard-code this and hard-code it for only two > > arches > > Especially that amd64 hosts only _usually_ can run i386. It's a kernel > config option that happens to be enabled in Debian kernels, but may be > omitted from derivative or self-built ones, usually for reasons of space and > security (compat syscalls and ioctls are a source of bugs, sometimes > exploitable). Thus, CONFIG_IA32_EMULATION might or might not be enabled. Yes, this is a good reason to do a run-time check. > On x86 I'm not aware of any 64-bit only hardware, but elsewhere, 32-bit > compat is optional -- skipping it can make chips cheaper and more > power-efficient, thus arm64 is often incapable of running armhf or armel. It is optional but not "often" omitted. I'm only aware of Cavium leaving it out. > Even on armhf, the manufacturer may choose to skip costly synchronization > needed for obsolete SWP instructions required by armel, which means > debootstrap (strictly single-threaded I think) will succeed but installed > system will run into mysterious corruption. [...] I think you're referring to the need for DMB on v6+, right? The ARMv6 ARM claims that memory ordering wasn't specified at all in earlier architecture versions, so older code using SWP was not portable anyway. So far as I can see, OpenSSL still uses SWP when built for ARMv4/v5, and does not use DMB. We should really fix that. dietlibc also uses SWP without DMB - but then its ARMv6/v7 implementation and several other architectures (mips, ppc) are also lacking memory barriers, so I assume no-one really uses it in multithreaded programs. uclibc has some trivial wrappers around SWP that don't seem to be used any more. And... that's it, so far as I can see. Ben. -- Ben Hutchings Make three consecutive correct guesses and you will be considered an expert.
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