Patch "bpftool: Define a local bpf_perf_link to fix accessing its fields" has been added to the 6.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    bpftool: Define a local bpf_perf_link to fix accessing its fields

to the 6.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     bpftool-define-a-local-bpf_perf_link-to-fix-accessin.patch
and it can be found in the queue-6.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 17969d02c9e731b6ce8355f3a67e5304b6c3a4e5
Author: Alexander Lobakin <alobakin@xxxxx>
Date:   Fri Jul 7 10:54:23 2023 +0100

    bpftool: Define a local bpf_perf_link to fix accessing its fields
    
    [ Upstream commit 67a43462ee2405c94e985a747bdcb8e3a0d66203 ]
    
    When building bpftool with !CONFIG_PERF_EVENTS:
    
    skeleton/pid_iter.bpf.c:47:14: error: incomplete definition of type 'struct bpf_perf_link'
            perf_link = container_of(link, struct bpf_perf_link, link);
                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    tools/bpf/bpftool/bootstrap/libbpf/include/bpf/bpf_helpers.h:74:22: note: expanded from macro 'container_of'
                    ((type *)(__mptr - offsetof(type, member)));    \
                                       ^~~~~~~~~~~~~~~~~~~~~~
    tools/bpf/bpftool/bootstrap/libbpf/include/bpf/bpf_helpers.h:68:60: note: expanded from macro 'offsetof'
     #define offsetof(TYPE, MEMBER)  ((unsigned long)&((TYPE *)0)->MEMBER)
                                                      ~~~~~~~~~~~^
    skeleton/pid_iter.bpf.c:44:9: note: forward declaration of 'struct bpf_perf_link'
            struct bpf_perf_link *perf_link;
                   ^
    
    &bpf_perf_link is being defined and used only under the ifdef.
    Define struct bpf_perf_link___local with the `preserve_access_index`
    attribute inside the pid_iter BPF prog to allow compiling on any
    configs. CO-RE will substitute it with the real struct bpf_perf_link
    accesses later on.
    container_of() uses offsetof(), which does the necessary CO-RE
    relocation if the field is specified with `preserve_access_index` - as
    is the case for struct bpf_perf_link___local.
    
    Fixes: cbdaf71f7e65 ("bpftool: Add bpf_cookie to link output")
    Suggested-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
    Signed-off-by: Alexander Lobakin <alobakin@xxxxx>
    Signed-off-by: Quentin Monnet <quentin@xxxxxxxxxxxxx>
    Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
    Link: https://lore.kernel.org/bpf/20230707095425.168126-3-quentin@xxxxxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/tools/bpf/bpftool/skeleton/pid_iter.bpf.c b/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
index e2af8e5fb29ec..3a4c4f7d83d86 100644
--- a/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
+++ b/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
@@ -15,6 +15,11 @@ enum bpf_obj_type {
 	BPF_OBJ_BTF,
 };
 
+struct bpf_perf_link___local {
+	struct bpf_link link;
+	struct file *perf_file;
+} __attribute__((preserve_access_index));
+
 struct perf_event___local {
 	u64 bpf_cookie;
 } __attribute__((preserve_access_index));
@@ -45,10 +50,10 @@ static __always_inline __u32 get_obj_id(void *ent, enum bpf_obj_type type)
 /* could be used only with BPF_LINK_TYPE_PERF_EVENT links */
 static __u64 get_bpf_cookie(struct bpf_link *link)
 {
+	struct bpf_perf_link___local *perf_link;
 	struct perf_event___local *event;
-	struct bpf_perf_link *perf_link;
 
-	perf_link = container_of(link, struct bpf_perf_link, link);
+	perf_link = container_of(link, struct bpf_perf_link___local, link);
 	event = BPF_CORE_READ(perf_link, perf_file, private_data);
 	return BPF_CORE_READ(event, bpf_cookie);
 }