Messages in this thread | | | Date | Tue, 30 Mar 2004 10:33:50 -0500 (EST) | From | "Richard B. Johnson" <> | Subject | Re: [ACPI] Re: Linux 2.4.26-rc1 (cmpxchg vs 80386 build) |
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On Tue, 30 Mar 2004, Willy Tarreau wrote:
> > > > OK, so why not compile the cmpxchg instruction even on i386 targets > > > to let generic kernels stay compatible with everything, but disable > > > ACPI at boot if the processor does not feature cmpxchg ? This could > > > be helpful for boot/install kernels which try to support a wide > > > range of platforms, and may need ACPI to correctly enable interrupts > > > on others. > > > > > > Cheers, > > > Willy > > > > > > > Because it would get used (by the compiler) in other code as well! > > As soon as the 386 sees it, you get an "invalid instruction trap" > > and you are dead. > > That's not what I meant. I only meant to declare the cmpxchg() function.
It's not a function. It is actual op-codes. If you compile with '486 or higher, the C compiler is free to spew out these op-codes any time it thinks it's a viable instruction sequence. Since it basically replaces two other op-codes, gcc might certainly use if for optimization.
This is independent of the macro that is defined in a header to use this sequence .
[SNIPPED...]
Cheers, Dick Johnson Penguin : Linux version 2.4.24 on an i686 machine (797.90 BogoMips). Note 96.31% of all statistics are fiction.
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