On Thu, 2018-01-11 at 13:41 +0000, Andrew Cooper wrote: > On 11/01/18 13:03, David Woodhouse wrote: > > > > On Thu, 2018-01-04 at 00:15 +0000, Andrew Cooper wrote: > > > > > > + * We've got no usable stack so can't use a RETPOLINE thunk, and > > > are > > > + * further than +- 2G from the high mappings so couldn't use > > > JUMP_THUNK > > > + * even if was a non-RETPOLINE thunk. Futhermore, an LFENCE > > > isn't > > > + * necesserily safe to use at this point. > > > I count three typos, pedantry about ± and GiB aside. > > Late night? :) > Just one of many... > > I've found furthermore and necessarily. Where is the 3rd?
* even if IT was a … > > > - asm volatile ( "call *%[stb]\n" > > > + asm volatile ( "CALL_THUNK %[stb]\n" > > If you make that %V[stb] then... > > ... you don't need this. > That's fine in principle, except it isn't compatible with most of the > compilers we support. To use, the %V has to be hidden behind a > conditional macro, and I can't think of any remotely-clean way to do > that. In at least one incarnation I ended up with something like #ifndef CONFIG_RETPOLINE #define CALL_THUNK(reg) "call *%[" #reg "]" #else #define CALL_THUNK(reg) "CALL_THUNK %V[" #reg "]" #endif Or maybe I just insisted that it was called %[thunk_target] and my CALL_THUNK C macro doesn't even take an argument. I forget. Late night…
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