Re: [PATCH bpf-next] selftests/bpf: fix uprobe_multi compilation error

[Eduard Zingerman <eddyz87@gmail.com>]

On Thu, 2024-09-26 at 15:49 +0100, Alan Maguire wrote:
> When building selftests, the following was seen:
> 
> uprobe_multi.c: In function ‘trigger_uprobe’:
> uprobe_multi.c:108:40: error: ‘MADV_PAGEOUT’ undeclared (first use in this function)
>   108 |                 madvise(addr, page_sz, MADV_PAGEOUT);
>       |                                        ^~~~~~~~~~~~
> uprobe_multi.c:108:40: note: each undeclared identifier is reported only once for each function it appears in
> make: *** [Makefile:850: bpf-next/tools/testing/selftests/bpf/uprobe_multi] Error 1
> 
> ...even with updated UAPI headers. It seems the above value is
> defined in UAPI <linux/mman.h> but including that file triggers
> other redefinition errors.  Simplest solution is to add a
> guarded definition, as was done for MADV_POPULATE_READ.
> 
> Fixes: 3c217a182018 ("selftests/bpf: add build ID tests")
> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> ---

I was curious why this error is not triggered on my local machine or CI.
MADV_PAGEOUT is indeed defined in UAPI.
Selftests build picks it from host system header, which is
/usr/include/bits/mman-linux.h for my Fedora 40 setup.
The MADV_PAGEOUT was added by commit [1] back in 2019
(and should be available from Linux 5.4, I guess Alan uses a very old kernel).

I think that at some point in time we should adjust selftests to use
UAPI headers that come from the kernel being tested, not from the host.
Until that happens, I think this fix is fine.

[1] 1a4e58cce84e ("mm: introduce MADV_PAGEOUT")

Acked-by: Eduard Zingerman <eddyz87@gmail.com>

(I want back to 2019...)

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