On Tue, Jun 28, 2022 at 02:58:25AM +0200, Gustavo A. R. Silva wrote:
On Mon, Jun 27, 2022 at 09:40:52PM -0300, Jason Gunthorpe wrote:
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@xxxxxxxxx/
Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
---
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 ?
No. I think now we can easily workaround these sorts of problems with
something like this:
struct flex {
any_type any_member;
union {
type array[0];
__DECLARE_FLEX_ARRAY(type, array_flex);
};
};
Mmmh... nope; this doesn't work[1].
We need to think in a different strategy.
--
Gustavo
[1] https://godbolt.org/z/av79Pqbfz
