On Mon, Nov 20, 2017 at 6:34 PM, Josh Poimboeuf <jpoim...@redhat.com> wrote: > On Mon, Nov 20, 2017 at 09:07:44AM -0800, Andy Lutomirski wrote: >> + /* Save RDI, since we need a scratch register. */ >> + pushq %rdi >> + >> + /* >> + * x86 lacks a near absolute jump, and we can't jump to the real >> + * entry text with a relative jump, so we use a double trampoline. >> + */ >> + movq $entry_SYSCALL_64_stage2, %rdi >> + jmp *%rdi >> +END(entry_SYSCALL_64_trampoline) >> + >> + .popsection >> + >> +ENTRY(entry_SYSCALL_64_stage2) >> + /* >> + * Rather than polluting the normal SYSCALL path with stack switching >> + * nonsense, fix up our register state to match its expectations. >> + */ >> + UNWIND_HINT_EMPTY >> + popq %rdi >> + jmp entry_SYSCALL_64_after_hwframe >> +END(entry_SYSCALL_64_stage2) > > Is there a reason why you couldn't just do the following? > > pushq $entry_SYSCALL_64_after_hwframe > ret > > Then you wouldn't need the 2nd trampoline and the %rdi clobber. >
Good suggestion. Thanks! > -- > Josh
