Re: Lowest i386 CPU Model with proper C++ atomics

2020-09-12 Thread Joel Sherrill
On Fri, Sep 11, 2020, 5:02 PM Joel Sherrill wrote: > > > On Fri, Sep 11, 2020 at 4:36 PM Janne Blomqvist > wrote: > >> On Fri, Sep 11, 2020 at 6:52 PM Joel Sherrill wrote: >> > >> > Hi >> > >> > Over at RTEMS, we ran into a case where the C++ atomics may not be right >> > for one of the lower l

Re: Lowest i386 CPU Model with proper C++ atomics

2020-09-11 Thread Joel Sherrill
On Fri, Sep 11, 2020 at 4:36 PM Janne Blomqvist wrote: > On Fri, Sep 11, 2020 at 6:52 PM Joel Sherrill wrote: > > > > Hi > > > > Over at RTEMS, we ran into a case where the C++ atomics may not be right > > for one of the lower level x86 models. We will investigate whether it can > > be made righ

Re: Lowest i386 CPU Model with proper C++ atomics

2020-09-11 Thread Janne Blomqvist via Gcc
On Fri, Sep 11, 2020 at 6:52 PM Joel Sherrill wrote: > > Hi > > Over at RTEMS, we ran into a case where the C++ atomics may not be right > for one of the lower level x86 models. We will investigate whether it can > be made right but this has led to the discussion of dropping older models > and set

Re: Lowest i386 CPU Model with proper C++ atomics

2020-09-11 Thread Joel Sherrill
On Fri, Sep 11, 2020 at 1:40 PM Florian Weimer wrote: > * Joel Sherrill: > > > I don't know that we have a huge issue in making the i486 a minimum. > > I was proposing a Pentium II or P6 as a baseline since that moves you > > up to having a TBR and initial SMP support. > > Sorry, what's a TBR? >

Re: Lowest i386 CPU Model with proper C++ atomics

2020-09-11 Thread Florian Weimer
* Joel Sherrill: > I don't know that we have a huge issue in making the i486 a minimum. > I was proposing a Pentium II or P6 as a baseline since that moves you > up to having a TBR and initial SMP support. Sorry, what's a TBR? > But I think there are still embedded x86 clones that I am not sure

Re: Lowest i386 CPU Model with proper C++ atomics

2020-09-11 Thread Joel Sherrill
On Fri, Sep 11, 2020 at 1:07 PM Florian Weimer wrote: > * Joel Sherrill: > > > With that in mind, what's the lowest/oldest i386 CPU model we > > should consider as the new base model? > > The 80486 has a CMPXCHG instruction (4-byte CAS). Starting from CAS, > you can build the rest. There might

Re: Lowest i386 CPU Model with proper C++ atomics

2020-09-11 Thread Florian Weimer
* Joel Sherrill: > With that in mind, what's the lowest/oldest i386 CPU model we > should consider as the new base model? The 80486 has a CMPXCHG instruction (4-byte CAS). Starting from CAS, you can build the rest. There might be some caveats about the memory model implementation (it may not be