On Sun, Oct 4, 2015 at 1:00 PM, Uros Bizjak <ubiz...@gmail.com> wrote: > 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. >
We can use unaligned load and store to avoid crash. -- H.J.
