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With indexed-array types such as "ops" from
Documentation/netlink/specs/nlctrl.yaml, the generator creates code
such as:
int nlctrl_getfamily_rsp_parse(const struct nlmsghdr *nlh,
struct ynl_parse_arg *yarg)
{
struct nlctrl_getfamily_rsp *dst;
const struct nlattr *attr_ops;
const struct nlattr *attr;
struct ynl_parse_arg parg;
unsigned int n_ops = 0;
int i;
...
ynl_attr_for_each(attr, nlh, yarg->ys->family->hdr_len) {
unsigned int type = ynl_attr_type(attr);
if (type == CTRL_ATTR_FAMILY_ID) {
...
} else if (type == CTRL_ATTR_OPS) {
const struct nlattr *attr2;
attr_ops = attr;
ynl_attr_for_each_nested(attr2, attr) {
if (ynl_attr_validate(yarg, attr2))
return YNL_PARSE_CB_ERROR;
n_ops++;
}
} else {
...
}
}
if (n_ops) {
dst->ops = calloc(n_ops, sizeof(*dst->ops));
dst->_count.ops = n_ops;
i = 0;
parg.rsp_policy = &nlctrl_op_attrs_nest;
ynl_attr_for_each_nested(attr, attr_ops) {
...
}
}
return YNL_PARSE_CB_OK;
}
It is clear that due to the sequential nature of code execution, when
n_ops (initially zero) is incremented, attr_ops is also assigned from
the value of "attr" (the current iterator).
But some compilers, like gcc version 12.2.0 (Debian 12.2.0-14+deb12u1)
as distributed by Debian Bookworm, seem to be not sophisticated enough
to see this, and fail to compile (warnings treated as errors):
In file included from ../lib/ynl.h:10,
from nlctrl-user.c:9:
In function ‘ynl_attr_data_end’,
inlined from ‘nlctrl_getfamily_rsp_parse’ at nlctrl-user.c:427:3:
../lib/ynl-priv.h:209:44: warning: ‘attr_ops’ may be used uninitialized [-Wmaybe-uninitialized]
209 | return (char *)ynl_attr_data(attr) + ynl_attr_data_len(attr);
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
nlctrl-user.c: In function ‘nlctrl_getfamily_rsp_parse’:
nlctrl-user.c:341:30: note: ‘attr_ops’ was declared here
341 | const struct nlattr *attr_ops;
| ^~~~~~~~
It is a pity that we have to do this, but I see no other way than to
suppress the false positive by appeasing the compiler and initializing
the "*attr_{aspec.c_name}" variable with a bogus value (NULL). This will
never be used - at runtime it will always be overwritten when
"n_{struct[anest].c_name}" is non-zero.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://patch.msgid.link/20250915144414.1185788-1-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.