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

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Mon, Sep 21, 2015 at 3:40 PM, Hal Finkel <hfinkel@anl.gov> wrote:
> ----- Original Message -----
>> From: "H.J. Lu via cfe-dev" <cfe-dev@lists.llvm.org>
>> To: "GCC Development" <gcc@gcc.gnu.org>, cfe-dev@lists.llvm.org
>> Sent: Monday, September 21, 2015 11:27:18 AM
>> Subject: Re: [cfe-dev] RFC: Support x86 interrupt and exception handlers
>>
>> On Thu, Sep 17, 2015 at 12:26 PM, H.J. Lu <hjl.tools@gmail.com>
>> wrote:
>> > On Tue, Sep 15, 2015 at 1:11 PM, H.J. Lu <hjl.tools@gmail.com>
>> > 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.
>>
>> 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.
>>
>>
>> --
>> H.J.
>> ---
>> The interrupt and exception handlers are called by x86 processors.
>>  X86
>> hardware pushes information onto stack and calls the handler.  The
>> requirements are
>>
>> 1. Both interrupt and exception handlers must use the 'IRET'
>> instruction,
>> instead of the 'RET' instruction, to return from the handlers.
>> 2. All registers are callee-saved in interrupt and exception
>> handlers.
>> 3. The difference between interrupt and exception handlers is the
>> exception handler must pop 'ERROR_CODE' off the stack before the
>> 'IRET'
>> instruction.
>>
>> The design goals of interrupt and exception handlers for x86
>> processors
>> are:
>>
>> 1. No new calling convention in compiler.
>> 2. Support both 32-bit and 64-bit modes.
>> 3. Flexible for compilers to optimize.
>> 4. Easy to use by programmers.
>>
>> To implement interrupt and exception handlers for x86 processors, a
>> compiler should support:
>>
>> 1. void * __builtin_interrupt_data (void)
>>
>> This function returns a pointer to the return address pushed onto the
>> stack by processor.
>>
>> The __builtin_frame_address builtin isn't suitable for interrupt and
>> exception handlers since it returns the stack frame address on the
>> callee side and compiler may generate a new stack frame for stack
>> alignment.
>>
>> 2. 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.
>
> Instead of adding more builtins for these, why not simply model this by giving the handler function a non-trivial signature? So, for example, the interrupt handler would be:
>
>  void handler(void *);
>
> and the exception handler would be:
>
>   void handler(size_t);
>

Since x86 interrupt/exception handlers don't conform to any x86 psABI,
you need to modify compiler to generate proper codes for

void handler(void *);

Please take a look at interrupt/exception handlers section in Intel SDM
vol 3.

-- 
H.J.