On Thu, Jan 21, 2021 at 6:07 PM Sedat Dilek [off-list ref] wrote:

On Thu, Jan 21, 2021 at 9:53 PM Andrii Nakryiko
[off-list ref] wrote:

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On Thu, Jan 21, 2021 at 8:09 AM Sedat Dilek [off-list ref] wrote:

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On Thu, Jan 21, 2021 at 2:38 PM Arnaldo Carvalho de Melo
[off-list ref] wrote:

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Em Tue, Jan 12, 2021 at 04:27:59PM -0800, Tom Stellard escreveu:

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On 1/12/21 10:40 AM, Jiri Olsa wrote:

quoted

When processing kernel image build by clang we can
find some functions without the name, which causes
pahole to segfault.

Adding extra checks to make sure we always have
function's name defined before using it.

I backported this patch to pahole 1.19, and I can confirm it fixes the
segfault for me.

I'm applying v2 for this patch and based on your above statement I'm
adding a:

Tested-by: Tom Stellard <redacted>

Ok?

Who originally reported this?

The origin was AFAICS the thread where I asked initially [1].

Tom reported in the same thread in [2] that pahole segfaults.

Later in the thread Jiri offered a draft of this patch after doing some tests.

I have tested all diffs and v1 and v2 of Jiri's patch.
( Anyway, latest pahole ToT plus Jiri's patch did not solve my origin problem. )

Your original problem was with DWARF5 or DWARF4? I think you mentioned
both at some point, but I remember I couldn't repro DWARF4 problems.
If you still have problems, can you start a new thread with steps to
repro (including Kconfig, tooling versions, etc). And one for each
problem, no all at the same time, please. I honestly lost track of
what's still not working among those multiple intertwined email
threads, sorry about that.

I love people saying "I have a (one) problem." :-).

The origin was Debian kernel-team enabled BTF-debuginfo Kconfig.

My main focus is to be as close to Debian's kernel-config and if this
works well with (experimental) Linux DWARF v5 support I am a happy
guy.

I don't know what kernel config Debian is using, that's why I'm asking
for kernel config that does cause the problem. Because the one I'm
using doesn't. But this problem can be a result of a lot of things,
specific compiler and its version, specific kernel config, who knows
what else.

Do you want Nick's DWARF v5 patch-series as a base?

Arnaldo was going to figure out the DWARF v5 problem, so I'm leaving
it up to him. I'm curious about DWARF v4 problems because no one yet
reported that previously.

Thinking of DWARF-v4?
Use Nick's patchset or DWARF-v4 what is in Linux upstream means Linux
v5.11-rc4+?
What Git tree to use - Linus or one of your BPF/BTF folks?

I checked both v5.11-rc4 and the latest bpf-next with
CONFIG_DEBUG_INFO_DWARF4=y and CONFIG_DEBUG_INFO_BTF=y. I get no
warnings, everything works.

What version of pahole (latest Git) etc.?

Latest pahole built from Git, yes.

But let's not do it in a backwards manner with me telling you what
works (my environment, my config), rather you telling us what
*doesn't* work (your config, your environment), so that we can try to
reproduce.

- Sedat -

quoted

quoted

So up to you Arnaldo for the credits.

- Sedat -

[1] https://marc.info/?t=161036949500004&r=1&w=2
[2] https://marc.info/?t=161036949500004&r=1&w=2

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- Arnaldo

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-Tom

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Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
  btf_encoder.c | 8 ++++++--
  1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/btf_encoder.c b/btf_encoder.c
index 333973054b61..17f7a14f2ef0 100644
--- a/btf_encoder.c
+++ b/btf_encoder.c

@@ -72,6 +72,8 @@ static int collect_function(struct btf_elf *btfe, GElf_Sym *sym)
    if (elf_sym__type(sym) != STT_FUNC)
            return 0;
+   if (!elf_sym__name(sym, btfe->symtab))
+           return 0;
    if (functions_cnt == functions_alloc) {
            functions_alloc = max(1000, functions_alloc * 3 / 2);

@@ -730,9 +732,11 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force,
            if (!has_arg_names(cu, &fn->proto))
                    continue;
            if (functions_cnt) {
-                   struct elf_function *func;
+                   const char *name = function__name(fn, cu);
+                   struct elf_function *func = NULL;
-                   func = find_function(btfe, function__name(fn, cu));
+                   if (name)
+                           func = find_function(btfe, name);
                    if (!func || func->generated)
                            continue;
                    func->generated = true;

--

- Arnaldo