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authorDavid Vernet <void@manifault.com>2023-02-01 20:30:14 +0300
committerDaniel Borkmann <daniel@iogearbox.net>2023-02-02 02:25:14 +0300
commit98e6ab7a04353c95b1f4bad345d156ded865fd96 (patch)
tree05fdeb14c15c8074dce01875bba9532da3554521 /Documentation/bpf/kfuncs.rst
parent57e7c169cd6afa093d858b8edfb9bceaf2e1c93b (diff)
downloadlinux-98e6ab7a04353c95b1f4bad345d156ded865fd96.tar.xz
bpf: Document usage of the new __bpf_kfunc macro
Now that the __bpf_kfunc macro has been added to linux/btf.h, include a blurb about it in the kfuncs.rst file. In order for the macro to successfully render with .. kernel-doc, we'll also need to add it to the c_id_attributes array. Signed-off-by: David Vernet <void@manifault.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Stanislav Fomichev <sdf@google.com> Link: https://lore.kernel.org/bpf/20230201173016.342758-3-void@manifault.com
Diffstat (limited to 'Documentation/bpf/kfuncs.rst')
-rw-r--r--Documentation/bpf/kfuncs.rst20
1 files changed, 17 insertions, 3 deletions
diff --git a/Documentation/bpf/kfuncs.rst b/Documentation/bpf/kfuncs.rst
index 1a683225d080..0bd07b39c2a4 100644
--- a/Documentation/bpf/kfuncs.rst
+++ b/Documentation/bpf/kfuncs.rst
@@ -41,7 +41,7 @@ An example is given below::
__diag_ignore_all("-Wmissing-prototypes",
"Global kfuncs as their definitions will be in BTF");
- struct task_struct *bpf_find_get_task_by_vpid(pid_t nr)
+ __bpf_kfunc struct task_struct *bpf_find_get_task_by_vpid(pid_t nr)
{
return find_get_task_by_vpid(nr);
}
@@ -66,7 +66,7 @@ kfunc with a __tag, where tag may be one of the supported annotations.
This annotation is used to indicate a memory and size pair in the argument list.
An example is given below::
- void bpf_memzero(void *mem, int mem__sz)
+ __bpf_kfunc void bpf_memzero(void *mem, int mem__sz)
{
...
}
@@ -86,7 +86,7 @@ safety of the program.
An example is given below::
- void *bpf_obj_new(u32 local_type_id__k, ...)
+ __bpf_kfunc void *bpf_obj_new(u32 local_type_id__k, ...)
{
...
}
@@ -125,6 +125,20 @@ flags on a set of kfuncs as follows::
This set encodes the BTF ID of each kfunc listed above, and encodes the flags
along with it. Ofcourse, it is also allowed to specify no flags.
+kfunc definitions should also always be annotated with the ``__bpf_kfunc``
+macro. This prevents issues such as the compiler inlining the kfunc if it's a
+static kernel function, or the function being elided in an LTO build as it's
+not used in the rest of the kernel. Developers should not manually add
+annotations to their kfunc to prevent these issues. If an annotation is
+required to prevent such an issue with your kfunc, it is a bug and should be
+added to the definition of the macro so that other kfuncs are similarly
+protected. An example is given below::
+
+ __bpf_kfunc struct task_struct *bpf_get_task_pid(s32 pid)
+ {
+ ...
+ }
+
2.4.1 KF_ACQUIRE flag
---------------------