Re: [PATCH bpf-next] libbpf: poison strlcpy()

[Boris Burkov <boris@bur.io>]

On Thu, Jan 05, 2023 at 10:47:15AM -0800, sdf@google.com wrote:
> On 01/05, Rong Tao wrote:
> > From: Rong Tao <rongtao@cestc.cn>
> 
> > Since commit 9fc205b413b3("libbpf: Add sane strncpy alternative and use
> > it internally") introduce libbpf_strlcpy(), thus add strlcpy() to a poison
> > list to prevent accidental use of it.
> 
> > Signed-off-by: Rong Tao <rongtao@cestc.cn>
> 
> Acked-by: Stanislav Fomichev <sdf@google.com>
> 
> > ---
> >   tools/lib/bpf/libbpf_internal.h | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> > diff --git a/tools/lib/bpf/libbpf_internal.h
> > b/tools/lib/bpf/libbpf_internal.h
> > index 377642ff51fc..2d26ded383ca 100644
> > --- a/tools/lib/bpf/libbpf_internal.h
> > +++ b/tools/lib/bpf/libbpf_internal.h
> > @@ -20,8 +20,8 @@
> >   /* make sure libbpf doesn't use kernel-only integer typedefs */
> >   #pragma GCC poison u8 u16 u32 u64 s8 s16 s32 s64
> 
> > -/* prevent accidental re-addition of reallocarray() */
> > -#pragma GCC poison reallocarray
> > +/* prevent accidental re-addition of reallocarray()/strlcpy() */
> > +#pragma GCC poison reallocarray strlcpy

On my musl system, I believe this broke compilation, as string.h defines
strlcpy, and is included after this poisoning when compiling strset.c

FWIW, I could work around it by adding
#include <string.h>
above
#include <libbpf_internal.h>
in strset.c, since the poison doesn't apply to symbols that existed
before it ran, but this feels like a kludge, and not in the spirit of
the original poisoning patch..

I'm curious what the proper workaround should be for a libc that defines
strlcpy.

Thanks,
Boris

> 
> >   #include "libbpf.h"
> >   #include "btf.h"
> > --
> > 2.39.0
>