BTF loading failing on perf

BTF loading failing on perf

[Arnaldo Carvalho de Melo]

root@number:~# perf trace -e openat --max-events=1
libbpf: failed to read kernel BTF from '/sys/kernel/btf/vmlinux': -ENODEV
libbpf: failed to read kernel BTF from '/sys/kernel/btf/vmlinux': -ENODEV
     0.000 ( 0.016 ms): ptyxis-agent/4375 openat(dfd: CWD, filename: "/proc/6593/cmdline", flags: RDONLY|CLOEXEC) = 13
root@number:~#

openat(AT_FDCWD, "/sys/kernel/btf/vmlinux", O_RDONLY) = 258
mmap(NULL, 6519699, PROT_READ, MAP_PRIVATE, 258, 0) = -1 ENODEV (No such device)
libbpf: failed to read kernel BTF from '/sys/kernel/btf/vmlinux': -ENODEV

root@number:~# ls -la /sys/kernel/btf/vmlinux 
-r--r--r--. 1 root root 6519699 Jun  6 12:19 /sys/kernel/btf/vmlinux
root@number:~# uname -a
Linux number 6.14.9-300.fc42.x86_64 #1 SMP PREEMPT_DYNAMIC Thu May 29 14:27:53 UTC 2025 x86_64 GNU/Linux
root@number:~# head /etc/os-release 
NAME="Fedora Linux"
VERSION="42 (Workstation Edition)"
RELEASE_TYPE=stable
ID=fedora
VERSION_ID=42
VERSION_CODENAME=""
PLATFORM_ID="platform:f42"
PRETTY_NAME="Fedora Linux 42 (Workstation Edition)"
ANSI_COLOR="0;38;2;60;110;180"
LOGO=fedora-logo-icon
root@number:~# rpm -q glibc-devel
package glibc-devel is not installed
root@number:~# rpm -q glibc
glibc-2.41-5.fc42.x86_64
root@number:~# 

Reverting the patch below "cures" the problem.

⬢ [acme@toolbx perf-tools]$ git log --oneline -10 tools/lib/bpf/
370118ff875244d4 (HEAD -> perf-tools) Revert "libbpf: Use mmap to parse vmlinux BTF from sysfs"
90b83efa6701656e Merge tag 'bpf-next-6.16' of git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next
3c0421c93ce4ff0f libbpf: Use mmap to parse vmlinux BTF from sysfs
4e29128a9acec2a6 libbpf/btf: Fix string handling to support multi-split BTF
d0445d7dd3fd9b15 libbpf: Check bpf_map_skeleton link for NULL
fd5fd538a1f4b34c libbpf: Use proper errno value in nlattr
62e23f183839c3d7 libbpf: Improve BTF dedup handling of "identical" BTF types
41d4ce6df3f49453 bpf: Fix uninitialized values in BPF_{CORE,PROBE}_READ
358b1c0f56ebb699 libbpf: Use proper errno value in linker
8e64c387c942229c libbpf: Add identical pointer detection to btf_dedup_is_equiv()
⬢ [acme@toolbx perf-tools]$

root@number:~# perf -v
perf version 6.15.g370118ff8752
root@number:~# perf trace -e connect --max-events=5
     0.000 ( 0.021 ms): DNS Res~ver #4/7932 connect(fd: 102, uservaddr: { .family: LOCAL, path: /run/systemd/r }, addrlen: 42) = 0
     0.304 ( 0.013 ms): systemd-resolv/1420 connect(fd: 25, uservaddr: { .family: INET, port: 53, addr: 186.208.78.194 }, addrlen: 16) = 0
     0.371 ( 0.002 ms): systemd-resolv/1420 connect(fd: 26, uservaddr: { .family: INET, port: 53, addr: 186.208.78.194 }, addrlen: 16) = 0
     0.591 ( 0.009 ms): DNS Res~ver #2/7523 connect(fd: 104, uservaddr: { .family: LOCAL, path: /run/systemd/r }, addrlen: 42) = 0
     0.731 ( 0.006 ms): systemd-resolv/1420 connect(fd: 28, uservaddr: { .family: INET, port: 53, addr: 186.208.78.194 }, addrlen: 16) = 0
root@number:~# 

Ideas?

- Arnaldo

⬢ [acme@toolbx perf-tools]$ git bisect good
3c0421c93ce4ff0f5f2612666122c34fc941d569 is the first bad commit
commit 3c0421c93ce4ff0f5f2612666122c34fc941d569
Author: Lorenz Bauer <lmb@isovalent.com>
Date:   Tue May 20 14:01:19 2025 +0100

    libbpf: Use mmap to parse vmlinux BTF from sysfs
    
    Teach libbpf to use mmap when parsing vmlinux BTF from /sys. We don't
    apply this to fall-back paths on the regular file system because there
    is no way to ensure that modifications underlying the MAP_PRIVATE
    mapping are not visible to the process.
    
    Signed-off-by: Lorenz Bauer <lmb@isovalent.com>
    Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
    Tested-by: Alan Maguire <alan.maguire@oracle.com>
    Acked-by: Andrii Nakryiko <andrii@kernel.org>
    Link: https://lore.kernel.org/bpf/20250520-vmlinux-mmap-v5-3-e8c941acc414@isovalent.com

 tools/lib/bpf/btf.c | 89 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++------------------
 1 file changed, 71 insertions(+), 18 deletions(-)
⬢ [acme@toolbx perf-tools]$

Re: BTF loading failing on perf

[Leo Yan]

Hi Arnaldo,

On Fri, Jun 06, 2025 at 12:37:55PM -0300, Arnaldo Carvalho de Melo wrote:
> root@number:~# perf trace -e openat --max-events=1
> libbpf: failed to read kernel BTF from '/sys/kernel/btf/vmlinux': -ENODEV
> libbpf: failed to read kernel BTF from '/sys/kernel/btf/vmlinux': -ENODEV
>      0.000 ( 0.016 ms): ptyxis-agent/4375 openat(dfd: CWD, filename: "/proc/6593/cmdline", flags: RDONLY|CLOEXEC) = 13
> root@number:~#
> 
> openat(AT_FDCWD, "/sys/kernel/btf/vmlinux", O_RDONLY) = 258
> mmap(NULL, 6519699, PROT_READ, MAP_PRIVATE, 258, 0) = -1 ENODEV (No such device)
> libbpf: failed to read kernel BTF from '/sys/kernel/btf/vmlinux': -ENODEV

Have you included the commit below in the kernel side?

commit a539e2a6d51d1c12d89eec149ccc72ec561639bc
Author: Lorenz Bauer <lmb@isovalent.com>
Date:   Tue May 20 14:01:17 2025 +0100

    btf: Allow mmap of vmlinux btf
    
    User space needs access to kernel BTF for many modern features of BPF.
    Right now each process needs to read the BTF blob either in pieces or
    as a whole. Allow mmaping the sysfs file so that processes can directly
    access the memory allocated for it in the kernel.
    
    remap_pfn_range is used instead of vm_insert_page due to aarch64
    compatibility issues.
    
    Signed-off-by: Lorenz Bauer <lmb@isovalent.com>
    Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
    Tested-by: Alan Maguire <alan.maguire@oracle.com>
    Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
    Link: https://lore.kernel.org/bpf/20250520-vmlinux-mmap-v5-1-e8c941acc414@isovalent.com

Thanks,
Leo

Re: BTF loading failing on perf

[Andrii Nakryiko]

On Fri, Jun 6, 2025 at 9:14 AM Leo Yan <leo.yan@arm.com> wrote:
>
> Hi Arnaldo,
>
> On Fri, Jun 06, 2025 at 12:37:55PM -0300, Arnaldo Carvalho de Melo wrote:
> > root@number:~# perf trace -e openat --max-events=1
> > libbpf: failed to read kernel BTF from '/sys/kernel/btf/vmlinux': -ENODEV
> > libbpf: failed to read kernel BTF from '/sys/kernel/btf/vmlinux': -ENODEV
> >      0.000 ( 0.016 ms): ptyxis-agent/4375 openat(dfd: CWD, filename: "/proc/6593/cmdline", flags: RDONLY|CLOEXEC) = 13
> > root@number:~#
> >
> > openat(AT_FDCWD, "/sys/kernel/btf/vmlinux", O_RDONLY) = 258
> > mmap(NULL, 6519699, PROT_READ, MAP_PRIVATE, 258, 0) = -1 ENODEV (No such device)
> > libbpf: failed to read kernel BTF from '/sys/kernel/btf/vmlinux': -ENODEV
>
> Have you included the commit below in the kernel side?

It doesn't matter, libbpf should silently fallback to non-mmap() way,
and it clearly doesn't.

We need something like this:

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index f1d495dc66bb..37682908cb0f 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -1384,12 +1384,12 @@ static struct btf *btf_parse_raw_mmap(const
char *path, struct btf *base_btf)

        fd = open(path, O_RDONLY);
        if (fd < 0)
-               return libbpf_err_ptr(-errno);
+               return ERR_PTR(-errno);

        if (fstat(fd, &st) < 0) {
                err = -errno;
                close(fd);
-               return libbpf_err_ptr(err);
+               return ERR_PTR(err);
        }

        data = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
@@ -1397,7 +1397,7 @@ static struct btf *btf_parse_raw_mmap(const char
*path, struct btf *base_btf)
        close(fd);

        if (data == MAP_FAILED)
-               return libbpf_err_ptr(err);
+               return ERR_PTR(err);

        btf = btf_new(data, st.st_size, base_btf, true);
        if (IS_ERR(btf))

libbpf_err_ptr() should be used for user-facing API functions, they
return NULL on error and set errno, so checking for IS_ERR() is wrong
here.

Lorenz, can you please test and send a proper fix ASAP?

>
> commit a539e2a6d51d1c12d89eec149ccc72ec561639bc
> Author: Lorenz Bauer <lmb@isovalent.com>
> Date:   Tue May 20 14:01:17 2025 +0100
>
>     btf: Allow mmap of vmlinux btf
>
>     User space needs access to kernel BTF for many modern features of BPF.
>     Right now each process needs to read the BTF blob either in pieces or
>     as a whole. Allow mmaping the sysfs file so that processes can directly
>     access the memory allocated for it in the kernel.
>
>     remap_pfn_range is used instead of vm_insert_page due to aarch64
>     compatibility issues.
>
>     Signed-off-by: Lorenz Bauer <lmb@isovalent.com>
>     Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
>     Tested-by: Alan Maguire <alan.maguire@oracle.com>
>     Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
>     Link: https://lore.kernel.org/bpf/20250520-vmlinux-mmap-v5-1-e8c941acc414@isovalent.com
>
> Thanks,
> Leo

Re: BTF loading failing on perf

[Arnaldo Carvalho de Melo]

On Fri, Jun 06, 2025 at 09:20:57AM -0700, Andrii Nakryiko wrote:
> On Fri, Jun 6, 2025 at 9:14 AM Leo Yan <leo.yan@arm.com> wrote:
> > On Fri, Jun 06, 2025 at 12:37:55PM -0300, Arnaldo Carvalho de Melo wrote:
> > > root@number:~# perf trace -e openat --max-events=1
> > > libbpf: failed to read kernel BTF from '/sys/kernel/btf/vmlinux': -ENODEV
> > > libbpf: failed to read kernel BTF from '/sys/kernel/btf/vmlinux': -ENODEV
> > >      0.000 ( 0.016 ms): ptyxis-agent/4375 openat(dfd: CWD, filename: "/proc/6593/cmdline", flags: RDONLY|CLOEXEC) = 13
> > > root@number:~#
> > >
> > > openat(AT_FDCWD, "/sys/kernel/btf/vmlinux", O_RDONLY) = 258
> > > mmap(NULL, 6519699, PROT_READ, MAP_PRIVATE, 258, 0) = -1 ENODEV (No such device)
> > > libbpf: failed to read kernel BTF from '/sys/kernel/btf/vmlinux': -ENODEV
> >
> > Have you included the commit below in the kernel side?
> 
> It doesn't matter, libbpf should silently fallback to non-mmap() way,

Right, it has to work with older kernels, etc.

> and it clearly doesn't.

> We need something like this:
> +++ b/tools/lib/bpf/btf.c
> @@ -1384,12 +1384,12 @@ static struct btf *btf_parse_raw_mmap(const
> char *path, struct btf *base_btf)
> 
>         fd = open(path, O_RDONLY);
>         if (fd < 0)
> -               return libbpf_err_ptr(-errno);
> +               return ERR_PTR(-errno);
> 
>         if (fstat(fd, &st) < 0) {
>                 err = -errno;
>                 close(fd);
> -               return libbpf_err_ptr(err);
> +               return ERR_PTR(err);
>         }
> 
>         data = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
> @@ -1397,7 +1397,7 @@ static struct btf *btf_parse_raw_mmap(const char
> *path, struct btf *base_btf)
>         close(fd);
> 
>         if (data == MAP_FAILED)
> -               return libbpf_err_ptr(err);
> +               return ERR_PTR(err);
> 
>         btf = btf_new(data, st.st_size, base_btf, true);
>         if (IS_ERR(btf))
> 
> libbpf_err_ptr() should be used for user-facing API functions, they
> return NULL on error and set errno, so checking for IS_ERR() is wrong
> here.

And the only user of the above function is:

                btf = btf_parse_raw_mmap(sysfs_btf_path, NULL);
                if (IS_ERR(btf))
                        btf = btf__parse(sysfs_btf_path, NULL);

That expects ERR_PTR() to then use IS_ERR().

I think this could be automated with something like coccinnele(sp)?

Anyway, I tested the patch above and it seems to fix the issue, so:

Reported-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Reviewed-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>

- Arnaldo

 
> Lorenz, can you please test and send a proper fix ASAP?
> 
> >
> > commit a539e2a6d51d1c12d89eec149ccc72ec561639bc
> > Author: Lorenz Bauer <lmb@isovalent.com>
> > Date:   Tue May 20 14:01:17 2025 +0100
> >
> >     btf: Allow mmap of vmlinux btf
> >
> >     User space needs access to kernel BTF for many modern features of BPF.
> >     Right now each process needs to read the BTF blob either in pieces or
> >     as a whole. Allow mmaping the sysfs file so that processes can directly
> >     access the memory allocated for it in the kernel.
> >
> >     remap_pfn_range is used instead of vm_insert_page due to aarch64
> >     compatibility issues.
> >
> >     Signed-off-by: Lorenz Bauer <lmb@isovalent.com>
> >     Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> >     Tested-by: Alan Maguire <alan.maguire@oracle.com>
> >     Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
> >     Link: https://lore.kernel.org/bpf/20250520-vmlinux-mmap-v5-1-e8c941acc414@isovalent.com
> >
> > Thanks,
> > Leo

Re: BTF loading failing on perf

[Andrii Nakryiko]

On Fri, Jun 6, 2025 at 1:05 PM Arnaldo Carvalho de Melo <acme@kernel.org> wrote:
>
> On Fri, Jun 06, 2025 at 09:20:57AM -0700, Andrii Nakryiko wrote:
> > On Fri, Jun 6, 2025 at 9:14 AM Leo Yan <leo.yan@arm.com> wrote:
> > > On Fri, Jun 06, 2025 at 12:37:55PM -0300, Arnaldo Carvalho de Melo wrote:
> > > > root@number:~# perf trace -e openat --max-events=1
> > > > libbpf: failed to read kernel BTF from '/sys/kernel/btf/vmlinux': -ENODEV
> > > > libbpf: failed to read kernel BTF from '/sys/kernel/btf/vmlinux': -ENODEV
> > > >      0.000 ( 0.016 ms): ptyxis-agent/4375 openat(dfd: CWD, filename: "/proc/6593/cmdline", flags: RDONLY|CLOEXEC) = 13
> > > > root@number:~#
> > > >
> > > > openat(AT_FDCWD, "/sys/kernel/btf/vmlinux", O_RDONLY) = 258
> > > > mmap(NULL, 6519699, PROT_READ, MAP_PRIVATE, 258, 0) = -1 ENODEV (No such device)
> > > > libbpf: failed to read kernel BTF from '/sys/kernel/btf/vmlinux': -ENODEV
> > >
> > > Have you included the commit below in the kernel side?
> >
> > It doesn't matter, libbpf should silently fallback to non-mmap() way,
>
> Right, it has to work with older kernels, etc.
>
> > and it clearly doesn't.
>
> > We need something like this:
> > +++ b/tools/lib/bpf/btf.c
> > @@ -1384,12 +1384,12 @@ static struct btf *btf_parse_raw_mmap(const
> > char *path, struct btf *base_btf)
> >
> >         fd = open(path, O_RDONLY);
> >         if (fd < 0)
> > -               return libbpf_err_ptr(-errno);
> > +               return ERR_PTR(-errno);
> >
> >         if (fstat(fd, &st) < 0) {
> >                 err = -errno;
> >                 close(fd);
> > -               return libbpf_err_ptr(err);
> > +               return ERR_PTR(err);
> >         }
> >
> >         data = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
> > @@ -1397,7 +1397,7 @@ static struct btf *btf_parse_raw_mmap(const char
> > *path, struct btf *base_btf)
> >         close(fd);
> >
> >         if (data == MAP_FAILED)
> > -               return libbpf_err_ptr(err);
> > +               return ERR_PTR(err);
> >
> >         btf = btf_new(data, st.st_size, base_btf, true);
> >         if (IS_ERR(btf))
> >
> > libbpf_err_ptr() should be used for user-facing API functions, they
> > return NULL on error and set errno, so checking for IS_ERR() is wrong
> > here.
>
> And the only user of the above function is:
>
>                 btf = btf_parse_raw_mmap(sysfs_btf_path, NULL);
>                 if (IS_ERR(btf))
>                         btf = btf__parse(sysfs_btf_path, NULL);
>
> That expects ERR_PTR() to then use IS_ERR().
>
> I think this could be automated with something like coccinnele(sp)?
>
> Anyway, I tested the patch above and it seems to fix the issue, so:
>
> Reported-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> Reviewed-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
>

Just sent a quick fix to not leave this waiting over the weekend.
Thanks for catching and reporting, Arnaldo!

> - Arnaldo
>
>
> > Lorenz, can you please test and send a proper fix ASAP?
> >
> > >
> > > commit a539e2a6d51d1c12d89eec149ccc72ec561639bc
> > > Author: Lorenz Bauer <lmb@isovalent.com>
> > > Date:   Tue May 20 14:01:17 2025 +0100
> > >
> > >     btf: Allow mmap of vmlinux btf
> > >
> > >     User space needs access to kernel BTF for many modern features of BPF.
> > >     Right now each process needs to read the BTF blob either in pieces or
> > >     as a whole. Allow mmaping the sysfs file so that processes can directly
> > >     access the memory allocated for it in the kernel.
> > >
> > >     remap_pfn_range is used instead of vm_insert_page due to aarch64
> > >     compatibility issues.
> > >
> > >     Signed-off-by: Lorenz Bauer <lmb@isovalent.com>
> > >     Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> > >     Tested-by: Alan Maguire <alan.maguire@oracle.com>
> > >     Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
> > >     Link: https://lore.kernel.org/bpf/20250520-vmlinux-mmap-v5-1-e8c941acc414@isovalent.com
> > >
> > > Thanks,
> > > Leo

Re: BTF loading failing on perf

[Arnaldo Carvalho de Melo]

On Fri, Jun 06, 2025 at 05:05:35PM -0300, Arnaldo Carvalho de Melo wrote:
> On Fri, Jun 06, 2025 at 09:20:57AM -0700, Andrii Nakryiko wrote:
> > On Fri, Jun 6, 2025 at 9:14 AM Leo Yan <leo.yan@arm.com> wrote:
> > > On Fri, Jun 06, 2025 at 12:37:55PM -0300, Arnaldo Carvalho de Melo wrote:
> > > > root@number:~# perf trace -e openat --max-events=1
> > > > libbpf: failed to read kernel BTF from '/sys/kernel/btf/vmlinux': -ENODEV
> > > > libbpf: failed to read kernel BTF from '/sys/kernel/btf/vmlinux': -ENODEV
> > > >      0.000 ( 0.016 ms): ptyxis-agent/4375 openat(dfd: CWD, filename: "/proc/6593/cmdline", flags: RDONLY|CLOEXEC) = 13
> > > > root@number:~#
> > > >
> > > > openat(AT_FDCWD, "/sys/kernel/btf/vmlinux", O_RDONLY) = 258
> > > > mmap(NULL, 6519699, PROT_READ, MAP_PRIVATE, 258, 0) = -1 ENODEV (No such device)
> > > > libbpf: failed to read kernel BTF from '/sys/kernel/btf/vmlinux': -ENODEV
> > >
> > > Have you included the commit below in the kernel side?
> > 
> > It doesn't matter, libbpf should silently fallback to non-mmap() way,
> 
> Right, it has to work with older kernels, etc.
> 
> > and it clearly doesn't.
> 
> > We need something like this:
> > +++ b/tools/lib/bpf/btf.c
> > @@ -1384,12 +1384,12 @@ static struct btf *btf_parse_raw_mmap(const
> > char *path, struct btf *base_btf)
> > 
> >         fd = open(path, O_RDONLY);
> >         if (fd < 0)
> > -               return libbpf_err_ptr(-errno);
> > +               return ERR_PTR(-errno);
> > 
> >         if (fstat(fd, &st) < 0) {
> >                 err = -errno;
> >                 close(fd);
> > -               return libbpf_err_ptr(err);
> > +               return ERR_PTR(err);
> >         }
> > 
> >         data = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
> > @@ -1397,7 +1397,7 @@ static struct btf *btf_parse_raw_mmap(const char
> > *path, struct btf *base_btf)
> >         close(fd);
> > 
> >         if (data == MAP_FAILED)
> > -               return libbpf_err_ptr(err);
> > +               return ERR_PTR(err);
> > 
> >         btf = btf_new(data, st.st_size, base_btf, true);
> >         if (IS_ERR(btf))
> > 
> > libbpf_err_ptr() should be used for user-facing API functions, they
> > return NULL on error and set errno, so checking for IS_ERR() is wrong
> > here.
> 
> And the only user of the above function is:
> 
>                 btf = btf_parse_raw_mmap(sysfs_btf_path, NULL);
>                 if (IS_ERR(btf))
>                         btf = btf__parse(sysfs_btf_path, NULL);
> 
> That expects ERR_PTR() to then use IS_ERR().
> 
> I think this could be automated with something like coccinnele(sp)?
 
> Anyway, I tested the patch above and it seems to fix the issue, so:
 
> Reported-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> Reviewed-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Was this fixed/merged?

- Arnaldo

Re: BTF loading failing on perf

[Andrii Nakryiko]

On Tue, Jun 10, 2025 at 1:27 PM Arnaldo Carvalho de Melo
<acme@kernel.org> wrote:
>
> On Fri, Jun 06, 2025 at 05:05:35PM -0300, Arnaldo Carvalho de Melo wrote:
> > On Fri, Jun 06, 2025 at 09:20:57AM -0700, Andrii Nakryiko wrote:
> > > On Fri, Jun 6, 2025 at 9:14 AM Leo Yan <leo.yan@arm.com> wrote:
> > > > On Fri, Jun 06, 2025 at 12:37:55PM -0300, Arnaldo Carvalho de Melo wrote:
> > > > > root@number:~# perf trace -e openat --max-events=1
> > > > > libbpf: failed to read kernel BTF from '/sys/kernel/btf/vmlinux': -ENODEV
> > > > > libbpf: failed to read kernel BTF from '/sys/kernel/btf/vmlinux': -ENODEV
> > > > >      0.000 ( 0.016 ms): ptyxis-agent/4375 openat(dfd: CWD, filename: "/proc/6593/cmdline", flags: RDONLY|CLOEXEC) = 13
> > > > > root@number:~#
> > > > >
> > > > > openat(AT_FDCWD, "/sys/kernel/btf/vmlinux", O_RDONLY) = 258
> > > > > mmap(NULL, 6519699, PROT_READ, MAP_PRIVATE, 258, 0) = -1 ENODEV (No such device)
> > > > > libbpf: failed to read kernel BTF from '/sys/kernel/btf/vmlinux': -ENODEV
> > > >
> > > > Have you included the commit below in the kernel side?
> > >
> > > It doesn't matter, libbpf should silently fallback to non-mmap() way,
> >
> > Right, it has to work with older kernels, etc.
> >
> > > and it clearly doesn't.
> >
> > > We need something like this:
> > > +++ b/tools/lib/bpf/btf.c
> > > @@ -1384,12 +1384,12 @@ static struct btf *btf_parse_raw_mmap(const
> > > char *path, struct btf *base_btf)
> > >
> > >         fd = open(path, O_RDONLY);
> > >         if (fd < 0)
> > > -               return libbpf_err_ptr(-errno);
> > > +               return ERR_PTR(-errno);
> > >
> > >         if (fstat(fd, &st) < 0) {
> > >                 err = -errno;
> > >                 close(fd);
> > > -               return libbpf_err_ptr(err);
> > > +               return ERR_PTR(err);
> > >         }
> > >
> > >         data = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
> > > @@ -1397,7 +1397,7 @@ static struct btf *btf_parse_raw_mmap(const char
> > > *path, struct btf *base_btf)
> > >         close(fd);
> > >
> > >         if (data == MAP_FAILED)
> > > -               return libbpf_err_ptr(err);
> > > +               return ERR_PTR(err);
> > >
> > >         btf = btf_new(data, st.st_size, base_btf, true);
> > >         if (IS_ERR(btf))
> > >
> > > libbpf_err_ptr() should be used for user-facing API functions, they
> > > return NULL on error and set errno, so checking for IS_ERR() is wrong
> > > here.
> >
> > And the only user of the above function is:
> >
> >                 btf = btf_parse_raw_mmap(sysfs_btf_path, NULL);
> >                 if (IS_ERR(btf))
> >                         btf = btf__parse(sysfs_btf_path, NULL);
> >
> > That expects ERR_PTR() to then use IS_ERR().
> >
> > I think this could be automated with something like coccinnele(sp)?
>
> > Anyway, I tested the patch above and it seems to fix the issue, so:
>
> > Reported-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> > Reviewed-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> > Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
>
> Was this fixed/merged?

yes, this was applied to bpf tree (not bpf-next)

>
> - Arnaldo