On 2015-12-20, at 2:48 PM, Helge Deller wrote: > On 20.12.2015 20:39, John David Anglin wrote: >> On 2015-12-18, at 6:30 PM, Helge Deller wrote: >> >>> + /* Usually we don't have to restore %r20 (the system call number) >>> + * because it gets loaded in the delay slot of the branch external >>> + * instruction via the ldi instruction. >>> + * In some cases a register-to-register copy instruction might have >>> + * been used instead, in which case we need to copy the syscall >>> + * number into the source register before returning to userspace. >>> + */ >> >> I'm thinking it might be better to fix syscall() in glibc. The copy could be >> moved before ble and a nop placed delay slot. > > Yes, I think it should be fixed in glibc which makes it cleaner. > I looked at dietlibc. There a "nop" is being used. A "nop" implies %r20 needs to be restored. > > Nevertheless, it may happen anytime if people forget, that we will see a > "copy" there again, so IMHO it's probably safer to include the workaround in > kernel too. The current patch assumes regs->gr[source_reg] is restored. That needs to be checked given previous comment about %r20. Essentially, all syscall clobbered registers need to be restored. Can the user space stuff be avoided by jumping to the gateway entry point? Dave -- John David Anglin dave.anglin@xxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-parisc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
