Daniel Borkmann
2022-Jun-27 18:27 UTC
[PATCH][next] treewide: uapi: Replace zero-length arrays with flexible-array members
On 6/27/22 8:04 PM, Gustavo A. R. Silva wrote:> There is a regular need in the kernel to provide a way to declare > having a dynamically sized set of trailing elements in a structure. > Kernel code should always use ?flexible array members?[1] for these > cases. The older style of one-element or zero-length arrays should > no longer be used[2]. > > This code was transformed with the help of Coccinelle: > (linux-5.19-rc2$ spatch --jobs $(getconf _NPROCESSORS_ONLN) --sp-file script.cocci --include-headers --dir . > output.patch) > > @@ > identifier S, member, array; > type T1, T2; > @@ > > struct S { > ... > T1 member; > T2 array[ > - 0 > ]; > }; > > -fstrict-flex-arrays=3 is coming and we need to land these changes > to prevent issues like these in the short future: > > ../fs/minix/dir.c:337:3: warning: 'strcpy' will always overflow; destination buffer has size 0, > but the source string has length 2 (including NUL byte) [-Wfortify-source] > strcpy(de3->name, "."); > ^ > > Since these are all [0] to [] changes, the risk to UAPI is nearly zero. If > this breaks anything, we can use a union with a new member name. > > [1] https://en.wikipedia.org/wiki/Flexible_array_member > [2] https://www.kernel.org/doc/html/v5.16/process/deprecated.html#zero-length-and-one-element-arrays > > Link: https://github.com/KSPP/linux/issues/78 > Build-tested-by: https://lore.kernel.org/lkml/62b675ec.wKX6AOZ6cbE71vtF%25lkp at intel.com/ > Signed-off-by: Gustavo A. R. Silva <gustavoars at kernel.org> > --- > Hi all! > > JFYI: I'm adding this to my -next tree. :)Fyi, this breaks BPF CI: https://github.com/kernel-patches/bpf/runs/7078719372?check_suite_focus=true [...] progs/map_ptr_kern.c:314:26: error: field 'trie_key' with variable sized type 'struct bpf_lpm_trie_key' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end] struct bpf_lpm_trie_key trie_key; ^ 1 error generated. make: *** [Makefile:519: /tmp/runner/work/bpf/bpf/tools/testing/selftests/bpf/map_ptr_kern.o] Error 1 make: *** Waiting for unfinished jobs.... Error: Process completed with exit code 2.
Jason Gunthorpe
2022-Jun-28 00:40 UTC
[PATCH][next] treewide: uapi: Replace zero-length arrays with flexible-array members
On Mon, Jun 27, 2022 at 08:27:37PM +0200, Daniel Borkmann wrote:> On 6/27/22 8:04 PM, Gustavo A. R. Silva wrote: > > There is a regular need in the kernel to provide a way to declare > > having a dynamically sized set of trailing elements in a structure. > > Kernel code should always use ?flexible array members?[1] for these > > cases. The older style of one-element or zero-length arrays should > > no longer be used[2]. > > > > This code was transformed with the help of Coccinelle: > > (linux-5.19-rc2$ spatch --jobs $(getconf _NPROCESSORS_ONLN) --sp-file script.cocci --include-headers --dir . > output.patch) > > > > @@ > > identifier S, member, array; > > type T1, T2; > > @@ > > > > struct S { > > ... > > T1 member; > > T2 array[ > > - 0 > > ]; > > }; > > > > -fstrict-flex-arrays=3 is coming and we need to land these changes > > to prevent issues like these in the short future: > > > > ../fs/minix/dir.c:337:3: warning: 'strcpy' will always overflow; destination buffer has size 0, > > but the source string has length 2 (including NUL byte) [-Wfortify-source] > > strcpy(de3->name, "."); > > ^ > > > > Since these are all [0] to [] changes, the risk to UAPI is nearly zero. If > > this breaks anything, we can use a union with a new member name. > > > > [1] https://en.wikipedia.org/wiki/Flexible_array_member > > [2] https://www.kernel.org/doc/html/v5.16/process/deprecated.html#zero-length-and-one-element-arrays > > > > Link: https://github.com/KSPP/linux/issues/78 > > Build-tested-by: https://lore.kernel.org/lkml/62b675ec.wKX6AOZ6cbE71vtF%25lkp at intel.com/ > > Signed-off-by: Gustavo A. R. Silva <gustavoars at kernel.org> > > --- > > Hi all! > > > > JFYI: I'm adding this to my -next tree. :) > > Fyi, this breaks BPF CI: > > https://github.com/kernel-patches/bpf/runs/7078719372?check_suite_focus=true > > [...] > progs/map_ptr_kern.c:314:26: error: field 'trie_key' with variable sized type 'struct bpf_lpm_trie_key' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end] > struct bpf_lpm_trie_key trie_key; > ^This will break the rdma-core userspace as well, with a similar error: /usr/bin/clang-13 -DVERBS_DEBUG -Dibverbs_EXPORTS -Iinclude -I/usr/include/libnl3 -I/usr/include/drm -g -O2 -fdebug-prefix-map=/__w/1/s=. -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 -Wmissing-prototypes -Wmissing-declarations -Wwrite-strings -Wformat=2 -Wcast-function-type -Wformat-nonliteral -Wdate-time -Wnested-externs -Wshadow -Wstrict-prototypes -Wold-style-definition -Werror -Wredundant-decls -g -fPIC -std=gnu11 -MD -MT libibverbs/CMakeFiles/ibverbs.dir/cmd_flow.c.o -MF libibverbs/CMakeFiles/ibverbs.dir/cmd_flow.c.o.d -o libibverbs/CMakeFiles/ibverbs.dir/cmd_flow.c.o -c ../libibverbs/cmd_flow.c In file included from ../libibverbs/cmd_flow.c:33: In file included from include/infiniband/cmd_write.h:36: In file included from include/infiniband/cmd_ioctl.h:41: In file included from include/infiniband/verbs.h:48: In file included from include/infiniband/verbs_api.h:66: In file included from include/infiniband/ib_user_ioctl_verbs.h:38: include/rdma/ib_user_verbs.h:436:34: error: field 'base' with variable sized type 'struct ib_uverbs_create_cq_resp' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end] struct ib_uverbs_create_cq_resp base; ^ include/rdma/ib_user_verbs.h:644:34: error: field 'base' with variable sized type 'struct ib_uverbs_create_qp_resp' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end] struct ib_uverbs_create_qp_resp base; Which is why I gave up trying to change these.. Though maybe we could just switch off -Wgnu-variable-sized-type-not-at-end during configuration ? Jason