> On Fri, 2025-06-20 at 11:11 -0700, Alexei Starovoitov wrote: >> On Thu, Jun 19, 2025 at 3:02 PM Song Liu <song@xxxxxxxxxx> wrote: >> > + bpf_dynptr_from_mem(xattr_value, sizeof(xattr_value), 0, &value_ptr); >> >> https://github.com/kernel-patches/bpf/actions/runs/15767046528/job/44445539248 >> >> progs/cgroup_read_xattr.c:19:9: error: ‘bpf_dynptr_from_mem’ is static >> but used in inline function ‘read_xattr’ which is not static [-Werror] >> 19 | bpf_dynptr_from_mem(value, sizeof(value), 0, &value_ptr); >> > ^~~~~~~~~~~~~~~~~~~ >> >> >> Jose, >> >> Could you please help us understand this gcc-bpf error ? >> What does it mean? > > Not Jose, but was curious. > Some googling lead to the following C99 wording [1]: > > > An inline definition of a function with external linkage shall not > > contain a definition of a modifiable object with static storage > > duration, and shall not contain a reference to an identifier with > > internal linkage > > [1] https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf > 6.7.4 Function specifiers, paragraph 3 > > The helper is defined as `static`: > > static long (* const bpf_dynptr_from_mem)(...) = (void *) 197; > > While `read_xattr` has external linkage: > > __always_inline void read_xattr(struct cgroup *cgroup) > { > ... > bpf_dynptr_from_mem(value, sizeof(value), 0, &value_ptr); > ... > } > > I think that declaring `read_xattr` as `static` should help with gcc. Yes I agree that is the issue. It is a restriction introduced by C99. I wasn't aware of it so I had to look it up. If you need read_xattr to be accessible from other compilation units and inlinable, you may declare it as static inline and put it in a header file. It will then use the copies of the helper pointers in the other compilation units. Alternatively, with GCC you could try to add a direct declaration for the helper function to progs/cgroup_read_xattr.c, that doesnt need to use any static intermediate pointer: #if COMPILING_WITH_GCC long _bpf_dynptr_from_mem (...) __attribute__ ((kernel_helper (197))); #define bpf_dynptr_from_mem _bpf_dynptr_from_mem #endif
