[cfe-dev] RFC: Support x86 interrupt and exception handlers

H.J. Lu via cfe-dev cfe-dev at lists.llvm.org
Tue Sep 22 04:52:02 PDT 2015

On Tue, Sep 22, 2015 at 4:44 AM, David Chisnall
<David.Chisnall at cl.cam.ac.uk> wrote:
> On 22 Sep 2015, at 12:39, H.J. Lu via cfe-dev <cfe-dev at lists.llvm.org> wrote:
>> The center piece of my proposal is not to change how parameters
>> are passed in compiler.  As for user experience, the feedbacks on
>> my proposal from our users are very positive.
> Implementing the intrinsics for getting the current interrupt requires a lot of support code for it to actually be useful.  For it to be useful, you are requiring all of the C code to be run with interrupts disabled (and even that doesn’t work if you get a NMI in the middle).  Most implementations use a small amount of assembly to capture the interrupt cause and the register state on entry to the handler, then reenable interrupts while the C code runs.  This means that any interrupts (e.g. page faults, illegal instruction traps, whatever) that happen while the C code is running do not mask the values.  Accessing these values from *existing* C code is simply a matter of loading a field from a structure.

The above applies to with and without intrinsics.

> I’m really unconvinced by something that something with such a narrow use case (and one that encourages writing bad code) belongs in the compiler.
> David


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