On Wed, Aug 5, 2015 at 5:21 PM, Pavel Machek <pavel@xxxxxx> wrote: > Hi! > >> Add a document describing the process of adding a new system call, >> including the need for a flags argument for future compatibility, and >> covering 32-bit/64-bit concerns (albeit in an x86-centric way). >> >> Signed-off-by: David Drysdale <drysdale@xxxxxxxxxx> >> Reviewed-by: Michael Kerrisk <mtk.manpages@xxxxxxxxx> >> Reviewed-by: Eric B Munson <emunson@xxxxxxxxxx> >> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> >> Reviewed-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> >> --- >> Documentation/adding-syscalls.txt | 531 ++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 531 insertions(+) >> create mode 100644 Documentation/adding-syscalls.txt > > We usually align documentation to less than 80 columns, afaict. Ah, a few re-worded paragraphs crept over the limit. Reflowed. >> +call. To make sure that userspace programs can safely use flags between kernel >> +versions, check whether the flags value holds any unknown flags, and reject the >> +sycall (with EINVAL) if it does: > > syscall? Fixed, thanks. >> +New system call proposals, like any change to the kernel's API, should always >> +be cc'ed to linux-api@xxxxxxxxxxxxxxx > > . at and of sentence? Fixed. >> +System Calls Returning Elsewhere >> +-------------------------------- >> + >> +For most system calls, once the system call is complete the user program >> +continues exactly where it left off -- at the next instruction, with the same >> +stack and registers as before the system call, and with the same virtual >> +memory space. > > Umm. Normally we place return value in register. And I'm not sure.. do > syscalls preserve registers that are normally caller-clobbered in the ABI? Reworded to: For most system calls, once the system call is complete the user program continues exactly where it left off -- at the next instruction, with the stack the same and most of the registers the same as before the system call, and with the same virtual memory space. > Thanks, > Pavel Thanks for the updates, David > -- > (english) http://www.livejournal.com/~pavelmachek > (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
