On Fri, Sep 11, 2020 at 9:06 AM Karel Gardas <karel.gar...@centrum.cz> wrote:
> On 9/11/20 3:13 PM, Joel Sherrill wrote: > > FWIW i386 is an 80s CPU introduced in 1985. i486 was introduced > > in 1989. The Pentium was 1993. Remember It's All About the Pentium! > > Pentium II was 1997 and first with SMP but maybe not setting the baseline > > we want. > > What about to support in master what man can currently purchase? If so, > then based on my limited research it looks like the cpu family > (orderable) goes back to 2016/2015 which support architecture of more or > less NetBurst uarch isn set (both intel and amd). > > One exception found is Vertex86 cpus which still sells and boards are > available and which are compatible only with i586/p5 from as you noted > 1993... > Karel: Typo correction: Vortex86: https://en.wikipedia.org/wiki/Vortex86 If I am reading that right, we may be ok dumping i386 and i486 completely and assuming around a Pentium II as default. Rather than a blanket drop 32-bit support which kills a LOT of usable functionality, I would rather find a new floor for the CPU model. My recollection from SMP testing i386 on qemu was that the lowest CPU model on Qemu that worked was core2duo which pc586-sse matches for GCC arguments. CPU_CFLAGS = -mtune=pentium -march=pentium -msse2 Is that lower than the broken code in GCC? What's the lowest multilib where the atomics are right? Assuming that it isn't just a bug below that level. I would like to pick a floor based on some reasonable rationale like GCC needs feature X for atomics which appears in CPU model Y. I don't think Qemu provides a rationale for a floor. Availability of SoCs for embedded systems seems like a short list and the wikipedia page doesn't encourage me that they are viable options as most look dead or barely breathing (parrot is dead): https://en.wikipedia.org/wiki/List_of_x86_manufacturers That leaves us with what's the lowest multilib in GCC where atomics work (or can be fixed, assuming this is a bug). --joel > Karel >
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