On Mon, Jul 28, 2014 at 11:01:02PM +0100, Peter Maydell wrote: > On 28 July 2014 22:42, Aurelien Jarno <aurel...@aurel32.net> wrote: > > On Mon, Jul 28, 2014 at 11:58:22PM +0800, Dongxue Zhang wrote: > >> Use 'if' to make sure the real msb greater than the lsb. As the compiler > >> may > >> not do this. > > > > What are you trying to fix exactly? These cases are defined as > > "unpredictable" in the MIPS ISA manual, which is what is implemented in > > QEMU. > > This may be true, but the TCG README doesn't define negative > lengths as being "unspecified behaviour" (ie guaranteed to at > least not crash even if the result isn't specified), and in fact the > implementation of tcg_gen_deposit will assert on negative lengths. > We shouldn't implement guest unpredictable cases as "crash QEMU".
Well I tried this code under QEMU, and it clearly doesn't crash. It seems the assert are not enabled with the default configuration options. That said I agree it's something to avoid, but I don't think triggering a RI exception is the thing to do (even if it is correct according the MIPS ISA manual) when real silicon output a random result instead. -- Aurelien Jarno GPG: 4096R/1DDD8C9B aurel...@aurel32.net http://www.aurel32.net
