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Message-ID: <202209261920.3A2EA07D4@keescook> Date: Mon, 26 Sep 2022 19:22:30 -0700 From: Kees Cook <keescook@...omium.org> To: Jakub Kicinski <kuba@...nel.org> Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>, Subash Abhinov Kasiviswanathan <quic_subashab@...cinc.com>, Sean Tranchetti <quic_stranche@...cinc.com>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH][next] net: ethernet: rmnet: Replace zero-length array with DECLARE_FLEX_ARRAY() helper On Mon, Sep 26, 2022 at 05:26:04PM -0700, Jakub Kicinski wrote: > On Mon, 26 Sep 2022 15:02:48 -0700 Kees Cook wrote: > > On Mon, Sep 26, 2022 at 04:50:03PM -0500, Gustavo A. R. Silva wrote: > > > Zero-length arrays are deprecated and we are moving towards adopting > > > C99 flexible-array members, instead. So, replace zero-length arrays > > > declarations in anonymous union with the new DECLARE_FLEX_ARRAY() > > > helper macro. > > > > > > This helper allows for flexible-array members in unions. > > > > > > Link: https://github.com/KSPP/linux/issues/193 > > > Link: https://github.com/KSPP/linux/issues/221 > > > Link: https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html > > > Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org> > > > > Reviewed-by: Kees Cook <keescook@...omium.org> > > Not directly related to this patch, but I just had to look at pahole > output for sk_buff and the struct_group() stuff makes is really painful > to read :/ Offsets for the members are relative to the "group" and they > are all repeated. > > Is there any chance you could fix that? Before we sprinkle more pixie > dust around, perhaps? Unfortunately I don't see a way around it until we can make changes to the C language spec, and that's measured in decades. :( Perhaps we could add some kind of heuristic to pahole to "hide" one of the internal struct_group() copies, and to hide the empty flexible-array wrapper structs? (pahole already can't tell the difference between a 0-length array and a flexible-array.) Would that be workable? -- Kees Cook
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