Subject: Re: [bpf-next,v3,11/13] tools: bpf: make use of reallocarray

From: Jakub Kicinski <[email-masked]>
Date: Fri, 13 Jul 2018 18:16:26 -0700

On Fri, 13 Jul 2018 17:31:34 -0700, Guenter Roeck wrote:
> On 07/13/2018 05:07 PM, Jakub Kicinski wrote:
> > On Fri, 13 Jul 2018 16:53:05 -0700, Guenter Roeck wrote:  
> >> Hi,
> >>
> >> On Tue, Jul 10, 2018 at 02:43:05PM -0700, Jakub Kicinski wrote:  
> >>> reallocarray() is a safer variant of realloc which checks for
> >>> multiplication overflow in case of array allocation.  Since it's
> >>> not available in Glibc < 2.26 import kernel's overflow.h and
> >>> add a static inline implementation when needed.  Use feature
> >>> detection to probe for existence of reallocarray.
> >>>      
> >>
> >> This probe doesn't work on my system (Ubuntu 16.04).
> >>
> >> libbpf.c: In function ‘bpf_object__add_program’:
> >> libbpf.c:326:10: error: implicit declaration of function ‘reallocarray’  
> > 
> > No way :( :(  Maybe you have to clean the build directory hard?
> > Maybe you have old feature check results or some such?
> >   
> 
> Unlikely. This is seen by my test builders which always start from a clean state.
> 
> $ lsb_release -a
> No LSB modules are available.
> Distributor ID:	Ubuntu
> Description:	Ubuntu 16.04.4 LTS
> Release:	16.04
> Codename:	xenial
> $ gcc --version
> gcc (Ubuntu 5.4.0-6ubuntu1~16.04.10) 5.4.0 20160609
> Copyright (C) 2015 Free Software Foundation, Inc.
> This is free software; see the source for copying conditions.  There is NO
> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
> $ ld --version
> GNU ld (GNU Binutils for Ubuntu) 2.26.1
> Copyright (C) 2015 Free Software Foundation, Inc.
> This program is free software; you may redistribute it under the terms of
> the GNU General Public License version 3 or (at your option) a later version.
> This program has absolutely no warranty.
> $ git describe
> next-20180713
> $ git clean -d -x -f -q
> $ make allmodconfig
> $ make tools/perf
> ...
> libbpf.c: In function ‘bpf_object__add_program’:
> libbpf.c:326:10: error: implicit declaration of function ‘reallocarray’

Oh, you're not building perf!  Looks like I missed adding reallocarray
to the default feature set on which perf depends, and since given that
features get reused (libbpf won't get to run its own feature detection)
we have to test for reallocarray there:

diff --git a/tools/build/Makefile.feature b/tools/build/Makefile.feature
index 5b6dda3b1ca8..f216b2f5c3d7 100644
--- a/tools/build/Makefile.feature
+++ b/tools/build/Makefile.feature
@@ -57,6 +57,7 @@ FEATURE_TESTS_BASIC :=                  \
         libunwind-aarch64               \
         pthread-attr-setaffinity-np     \
         pthread-barrier                \
+        reallocarray                    \
         stackprotector-all              \
         timerfd                         \
         libdw-dwarf-unwind              \