Em Thu, Oct 01, 2020 at 09:50:29AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Thu, Oct 01, 2020 at 12:33:18PM +0200, Toke Høiland-Jørgensen escreveu:
> > Kevin Sheldrake <Kevin.Sheldrake@xxxxxxxxxxxxx> writes:
> > > I've seen mention a few times that BTF information can be made
> > > available from a kernel that wasn't configured with
> > > CONFIG_DEBUG_INFO_BTF. Please can someone tell me if this is true and,
> > > if so, how I could go about accessing and using it in kernels 4.15 to
> > > 5.8?
> > > I have built the dwarves package from the github latest and run pahole
> > > with '-J' against my kernel image to no avail - it actually seg
> > > faults:
> > > ~/dwarves/build $ sudo ./pahole /boot/vmlinuz-5.3.0-1022-azure
> > > btf_elf__new: cannot get elf header.
> > > ctf__new: cannot get elf header.
> > > ~/dwarves/build $ sudo ./pahole -J /boot/vmlinuz-5.3.0-1022-azure
> > > btf_elf__new: cannot get elf header.
> > > ctf__new: cannot get elf header.
> > > Segmentation fault
> > > ~/dwarves/build $ sudo ./pahole --version
> > > v1.17
> > > Judging by the output, I'm guessing that my kernel image isn't the
> > > right kind of file. Can someone point me in the right direction?
> > vmlinuz is a compressed image. There's a script in the kernel source
> > tree (scripts/extract-vmlinux), however the kernel image in /boot/
> > probably also has debug information stripped from it, so that likely
> > won't help you. You'll need to get hold of a kernel image with debug
> > information still intact somehow...
> > (Either way, pahole shouldn't be segfaulting, so hopefully someone can
> > take a look at that).
> Reproduced:
> [acme@five pahole]$ cp /boot/vmlinuz-5.9.0-rc6+ .
> [acme@five pahole]$ pahole -J vmlinuz-5.9.0-rc6+
> btf_elf__new: cannot get elf header.
> ctf__new: cannot get elf header.
> tag__check_id_drift: subroutine_type id drift, core_id: 1145, btf_type_id: 1143, type_id_off: 0
> pahole: type 'vmlinuz-5.9.0-rc6+' not found
> libbpf: Unsupported BTF_KIND:0
> btf_elf__encode: btf__new failed!
> free(): double free detected in tcache 2
> Aborted (core dumped)
> [acme@five pahole]$
> Working on a fix. Thanks for the report!
commit 4e55425d9eaac78689fbd296283e1557bb6ca725
Author: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Date: Thu Oct 1 10:10:50 2020 -0300
pahole: Only try using a single file name as a type name if not encoding BTF or CTF
Otherwise we end up trying to encode without any debug info and this
causes a segfault:
Before:
$ pahole -J vmlinuz-5.9.0-rc6+
tag__check_id_drift: subroutine_type id drift, core_id: 1145, btf_type_id: 1143, type_id_off: 0
pahole: type 'vmlinuz-5.9.0-rc6+' not found
libbpf: Unsupported BTF_KIND:0
btf_elf__encode: btf__new failed!
free(): double free detected in tcache 2
Aborted (core dumped)
$
The vmlinuz file doesn't contain any debugging info, fixing it we get:
$ pahole -J vmlinuz-5.9.0-rc6+
pahole: vmlinuz-5.9.0-rc6+: No debugging information found
$
If debugging info is available, it all works as before:
Using /sys/kernel/btf/vmlinux
$ ls -la /sys/kernel/btf/vmlinux
-r--r--r--. 1 root root 3393761 Oct 1 09:50 /sys/kernel/btf/vmlinux
$ pahole -E fw_cache_entry
struct fw_cache_entry {
struct list_head {
struct list_head * next; /* 0 8 */
struct list_head * prev; /* 8 8 */
} list; /* 0 16 */
const char * name; /* 16 8 */
/* size: 24, cachelines: 1, members: 2 */
/* last cacheline: 24 bytes */
};
$
Or explicitely asking for DWARF, where it will find the appropriate
vmlinux according to its buildid in /sys/kernel/notes:
$ pahole -F dwarf pm_clock_entry
struct pm_clock_entry {
struct list_head node; /* 0 16 */
char * con_id; /* 16 8 */
struct clk * clk; /* 24 8 */
enum pce_status status; /* 32 4 */
/* size: 40, cachelines: 1, members: 4 */
/* padding: 4 */
/* last cacheline: 40 bytes */
};
$ pahole -F dwarf --expand_types pm_clock_entry
struct pm_clock_entry {
struct list_head {
struct list_head * next; /* 0 8 */
struct list_head * prev; /* 8 8 */
} node; /* 0 16 */
char * con_id; /* 16 8 */
struct clk * clk; /* 24 8 */
enum pce_status status; /* 32 4 */
/* size: 40, cachelines: 1, members: 4 */
/* padding: 4 */
/* last cacheline: 40 bytes */
};
$
Reported-by: Kevin Sheldrake <Kevin.Sheldrake@xxxxxxxxxxxxx>
Cc: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
diff --git a/pahole.c b/pahole.c
index ee5f2f7f76b0f1d6..dac7a492a266e7f1 100644
--- a/pahole.c
+++ b/pahole.c
@@ -2686,7 +2686,7 @@ try_sole_arg_as_class_names:
err = cus__load_files(cus, &conf_load, argv + remaining);
if (err != 0) {
- if (class_name == NULL) {
+ if (class_name == NULL && !btf_encode && !ctf_encode) {
class_name = argv[remaining];
remaining = argc;
goto try_sole_arg_as_class_names;
