Date: Thu, 18 Sep 2025 20:17:41 +0900 From: Nakayama Kenjiro <nakayamakenjiro@gmail.com> To: freebsd-hackers@freebsd.org Cc: freebsd-net@freebsd.org Subject: Build failure with Clang/LLVM 22 due to alloc-size diagnostic Message-ID: <CAA_ZtA_184k892=5v0OtZsjweWSgSCX%2BWWR6se_aVCJCAh-apQ@mail.gmail.com>
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--0000000000000587f9063f11812c Content-Type: text/plain; charset="UTF-8" Hi, There is a new diagnostic, alloc-size, in clang of LLVM22 that warns if the size given to a malloc is smaller than the size of the struct pointed to by its destination - https://github.com/llvm/llvm-project/pull/150028 When we enable this option, in_mcast.c triggers this diagnostic, causing the build to fail. ``` freebsd/sys/netinet/in_mcast.c:749:10: error: allocation of insufficient size '40' for type 'struct ip_msource' with size '48' [-Werror,-Walloc-size] 749 | nims = malloc(sizeof(struct in_msource), M_INMFILTER, | ^ ``` https://github.com/freebsd/freebsd-src/blob/stable/15/sys/netinet/in_mcast.c#L749 ``` static int imf_get_source(struct in_mfilter *imf, const struct sockaddr_in *psin, struct in_msource **plims) { ... struct ip_msource *ims, *nims; ... nims = malloc(sizeof(struct in_msource), M_INMFILTER, M_NOWAIT | M_ZERO); ``` As the error message explained, the mismatch between struct ip_msource * and malloc(sizeof(struct in_msource)) triggers the error. However, when reading the source code carefully, it seems that *nims is intentionally of type ip_msource instead of in_msource. I would like to build with LLVM's alloc-size option enabled, but does anyone have any good ideas on how to address this problem? Or would it be better to report it as a false positive to LLVM? Though, I am aware that there is a workaround to partially disable this option... --0000000000000587f9063f11812c Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable <div dir=3D"ltr"><div>Hi,</div><div><br></div><div>There is a new diagnosti= c, alloc-size, in clang of LLVM22 that warns if the size given to a malloc = is smaller than the size of the struct pointed to by its destination - <a h= ref=3D"https://github.com/llvm/llvm-project/pull/150028">https://github.com= /llvm/llvm-project/pull/150028</a><br>When we enable this option, in_mcast.= c triggers this diagnostic, causing the build to fail.<br><br>```<br>freebs= d/sys/netinet/in_mcast.c:749:10: error: allocation of insufficient size = 9;40' for type 'struct ip_msource' with size '48' [-Wer= ror,-Walloc-size]<br>=C2=A0 749 | =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0= =C2=A0 =C2=A0 nims =3D malloc(sizeof(struct in_msource), M_INMFILTER,<br>= =C2=A0 =C2=A0 =C2=A0 | =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0^<br>```<br><br><a href=3D"https://github.co= m/freebsd/freebsd-src/blob/stable/15/sys/netinet/in_mcast.c#L749">https://g= ithub.com/freebsd/freebsd-src/blob/stable/15/sys/netinet/in_mcast.c#L749</a= ><br>```<br>static int<br>imf_get_source(struct in_mfilter *imf, const stru= ct sockaddr_in *psin,<br>=C2=A0 =C2=A0 struct in_msource **plims)<br>{<br>= =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 ...<br> struct ip_msource *ims, *nims;<b= r> =C2=A0 ...<br> nims =3D malloc(sizeof(struct in_msource), M_INMFILTER,= <br> =C2=A0 =C2=A0M_NOWAIT | M_ZERO);<br>```<br><br>As the error message = explained, the mismatch between struct ip_msource * and malloc(sizeof(struc= t in_msource)) triggers the error.<br><br>However, when reading the source = code carefully, it seems that *nims is intentionally of type ip_msource ins= tead of in_msource.<br>I would like to build with LLVM's alloc-size opt= ion enabled, but does anyone have any good ideas on how to address this pro= blem? Or would it be better to report it as a false positive to LLVM? Thoug= h, I am aware that there is a workaround to partially disable this option..= .</div></div> --0000000000000587f9063f11812c--
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