This is the mail archive of the
mailing list for the GCC project.
Re: [cfe-dev] RFC: Support x86 interrupt and exception handlers
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: John Criswell <jtcriswel at gmail dot com>
- Cc: GCC Development <gcc at gcc dot gnu dot org>, cfe-dev at lists dot llvm dot org
- Date: Mon, 21 Sep 2015 13:45:41 -0700
- Subject: Re: [cfe-dev] RFC: Support x86 interrupt and exception handlers
- Authentication-results: sourceware.org; auth=none
- References: <CAMe9rOpKPxK-79pBO-MyiMzGqd=9gxDxJdRnDvdq4UumUTakHQ at mail dot gmail dot com> <CAMe9rOp8hma_3b49oMjWeixLPTeiQFX2MUxSbftMNmfjP4A0-Q at mail dot gmail dot com> <CAMe9rOpOC43+AOBsp8CMdzhCMQrGqzjpj+zTzaZ=SDKmd4GB1w at mail dot gmail dot com> <CAMe9rOpRRuBxHXzEKhSOO67VPkUQnx=gVuMAxq0snyTFxF+gaA at mail dot gmail dot com> <560051EF dot 70405 at gmail dot com>
On Mon, Sep 21, 2015 at 11:52 AM, John Criswell <firstname.lastname@example.org> wrote:
> On 9/21/15 12:27 PM, H.J. Lu via cfe-dev wrote:
>> On Thu, Sep 17, 2015 at 12:26 PM, H.J. Lu <email@example.com> wrote:
>>> On Tue, Sep 15, 2015 at 1:11 PM, H.J. Lu <firstname.lastname@example.org> wrote:
>>>>> To implement interrupt and exception handlers for x86 processors, a
>>>>> compiler should support:
>>>>> 1. void * __builtin_ia32_interrupt_data (void)
>>>> I got a feedback on the name of this builtin function. Since
>>>> it also works for 64-bit, we should avoid ia32 in its name.
>>>> We'd like to change it to
>>>> void * __builtin_interrupt_data (void)
>>> Here is the updated spec.
>> This updated spec adds
>> unsigned int __builtin_exception_error (void)
>> unsigned long long int __builtin_exception_error (void)
>> This function returns the exception error code pushed onto the stack by
>> processor. Its return value is 64 bits in 64-bit mode and 32 bits in
>> 32-bit mode. This function can only be used in exception handler.
> Exception handlers can, in general, call regular functions which, in turn,
> might want to access the error code. Given that operating system kernels
> are always entered via an interrupt, trap, or system call, there should
> always be an error code available (on x86, non-error-code interrupts can
> just make up an error code).
>> It also changes the definition of
>> void * __builtin_interrupt_data (void)
>> so that it returns a pointer to the data layout pushed onto stack
>> by processor for both interrupt and exception handlers.
> You might want to have a look at Secure Virtual Architecture (SVA). One of
I believe my x86 interrupt attribute is unrelated to SVA.
> If the implementation is useful, SVA is publicly available at
> Finally, to echo Joerg's concerns, it's not clear that having
> exception/interrupt handlers declared as a special type is really helpful.
> It's not immediately obvious that you get a benefit from doing that vs.
> doing what most system software does (having assembly code that saves
> processor state and calls a C function). I think you should do some
> experiments to demonstrate the benefit that one can get with your method to
> see if it is worth adding complexity to the compiler.
The main purpose of x86 interrupt attribute is to allow programmers
to write x86 interrupt/exception handlers in C WITHOUT assembly
stubs to avoid extra branch from assembly stubs to C functions. I
want to keep the number of new intrinsics to minimum without sacrificing
handler performance. I leave faking error code in interrupt handler to