Re: [PATCH] samples: pidfd: Fix compile error seen if __NR_pidfd_send_signal is undefined

[Guenter Roeck]

On 5/30/19 4:43 AM, Christian Brauner wrote:
> On May 30, 2019 1:40:47 PM GMT+02:00, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > To make pidfd-metadata compile on all arches, irrespective of whether
> > or not syscall numbers are assigned, define the syscall number to -1
> > if it isn't to cause the kernel to return -ENOSYS.
> >
> > Fixes: 43c6afee48d4 ("samples: show race-free pidfd metadata access")
> > Cc: Christian Brauner <christian@xxxxxxxxxx>
> > Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > ---
> > samples/pidfd/pidfd-metadata.c | 4 ++++
> > 1 file changed, 4 insertions(+)
> >
> > diff --git a/samples/pidfd/pidfd-metadata.c
> > b/samples/pidfd/pidfd-metadata.c
> > index 640f5f757c57..1e125ddde268 100644
> > --- a/samples/pidfd/pidfd-metadata.c
> > +++ b/samples/pidfd/pidfd-metadata.c
> > @@ -21,6 +21,10 @@
> > #define CLONE_PIDFD 0x00001000
> > #endif
> >
> > +#ifndef __NR_pidfd_send_signal
> > +#define __NR_pidfd_send_signal	-1
> > +#endif
> > +
> > static int do_child(void *args)
> > {
> > 	printf("%d\n", getpid());
>
> Couldn't you just use the actual syscall number?
> That should still fail if the kernel is to old
> and still work on kernels that support it
> but for whatever reason the unistd.h h
> header doesn't have it defined.

syscall numbers can differ from architecture to architecture, and the
provided solution is used in other test code. Please feel free to submit
a different patch, though - I am only interested in a fix, which doesn't
have to be mine.

Note that this fails in mips builds.

Thanks,
Guenter