On Mon, Sep 21, 2015 at 11:52 AM, John Criswell <jtcris...@gmail.com> 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 <hjl.to...@gmail.com> wrote: >>> >>> On Tue, Sep 15, 2015 at 1:11 PM, H.J. Lu <hjl.to...@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. > > > 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 > https://github.com/jtcriswell/SVA. > > 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 the programmer. -- H.J.
