On Sun, Oct 4, 2015 at 8:15 PM, H.J. Lu <hjl.to...@gmail.com> wrote: >> Looking a bit deeper into the code, it looks that we want to realign >> the stack in the interrupt handler. Let's assume that interrupt >> handler is calling some other function that saves SSE vector regs to >> the stack. According to the x86 ABI, incoming stack of the called >> function is assumed to be aligned to 16 bytes. But, interrupt handler >> violates this assumption, since the stack could be aligned to only 4 >> bytes for 32bit and 8 bytes for 64bit targets. Entering the called >> function with stack, aligned to less than 16 bytes will certainly >> violate ABI. >> >> So, it looks to me that we need to realign the stack in the interrupt >> handler unconditionally to 16bytes. In this case, we also won't need >> the following changes: >> > > Current stack alignment implementation requires at least > one, maybe two, scratch registers: > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67841 > > Extend it to the interrupt handler, which doesn't have any scratch > registers may require significant changes in backend as well as > register allocator.
But without realignment, the handler is unusable for anything but simple functions. The handler will crash when called function will try to save vector reg to stack. Uros.
