Patch "bpftool: use a local copy of perf_event to fix accessing :: Bpf_cookie" 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: use a local copy of perf_event to fix accessing :: Bpf_cookie

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-use-a-local-copy-of-perf_event-to-fix-access.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 82504667ede030ac52b55ddd8a75134d1d7847ea
Author: Alexander Lobakin <alobakin@xxxxx>
Date:   Fri Jul 7 10:54:22 2023 +0100

    bpftool: use a local copy of perf_event to fix accessing :: Bpf_cookie
    
    [ Upstream commit 4cbeeb0dc02f8ac7b975b2ab0080ace53d43d62a ]
    
    When CONFIG_PERF_EVENTS is not set, struct perf_event remains empty.
    However, the structure is being used by bpftool indirectly via BTF.
    This leads to:
    
    skeleton/pid_iter.bpf.c:49:30: error: no member named 'bpf_cookie' in 'struct perf_event'
            return BPF_CORE_READ(event, bpf_cookie);
                   ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~
    
    ...
    
    skeleton/pid_iter.bpf.c:49:9: error: returning 'void' from a function with incompatible result type '__u64' (aka 'unsigned long long')
            return BPF_CORE_READ(event, bpf_cookie);
                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    
    Tools and samples can't use any CONFIG_ definitions, so the fields
    used there should always be present.
    Define struct perf_event___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 perf_event
    accesses later on.
    
    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/20230707095425.168126-2-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 eb05ea53afb12..e2af8e5fb29ec 100644
--- a/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
+++ b/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
@@ -15,6 +15,10 @@ enum bpf_obj_type {
 	BPF_OBJ_BTF,
 };
 
+struct perf_event___local {
+	u64 bpf_cookie;
+} __attribute__((preserve_access_index));
+
 extern const void bpf_link_fops __ksym;
 extern const void bpf_map_fops __ksym;
 extern const void bpf_prog_fops __ksym;
@@ -41,8 +45,8 @@ 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 perf_event___local *event;
 	struct bpf_perf_link *perf_link;
-	struct perf_event *event;
 
 	perf_link = container_of(link, struct bpf_perf_link, link);
 	event = BPF_CORE_READ(perf_link, perf_file, private_data);