linux-kernel - Re: [PATCH 05/23] selftest: vm: add unlikely() to BUG

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Date:   Thu, 30 Aug 2018 23:57:52 +0100
From:   Dmitry Safonov <dima@...sta.com>
To:     Igor Stoppa <igor.stoppa@...il.com>, linux-kernel@...r.kernel.org
Cc:     Igor Stoppa <igor.stoppa@...wei.com>, Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH 05/23] selftest: vm: add unlikely() to BUG_ON()

Hi Igor,

On Fri, 2018-08-31 at 01:34 +0300, Igor Stoppa wrote:
> BUG_ON() is unlikely() to BUG()

This selftest runs in userspace..
So, we should define the macro somehow, as i.e:
rseq/rseq.h:#define rseq_unlikely(x)    __builtin_expect(!!(x), 0)

Otherwise,
[selftests]$ make vm/map_populate
cc     vm/map_populate.c   -o vm/map_populate
vm/map_populate.c: In function ‘parent_f’:
vm/map_populate.c:26:7: warning: implicit declaration of function
‘unlikely’; did you mean ‘unlinkat’? [-Wimplicit-function-declaration]
   if (unlikely(condition)) {     \
       ^
vm/map_populate.c:38:2: note: in expansion of macro ‘BUG_ON’
  BUG_ON(ret <= 0, "read(sock)");
  ^~~~~~
/tmp/cc7evGVG.o: In function `parent_f':
map_populate.c:(.text+0x3d): undefined reference to `unlikely'
map_populate.c:(.text+0xbb): undefined reference to `unlikely'
map_populate.c:(.text+0x135): undefined reference to `unlikely'
map_populate.c:(.text+0x1b0): undefined reference to `unlikely'

Not sure if we care for this at all for userspace test.
I don't mind as it runs each time by kbuild robot and cumulatively may
save something. But it's better be at least compile-tested.

-- 
            Dima