On Tue, Sep 27, 2022 at 11:56 AM Nathan Chancellor <nathan@xxxxxxxxxx> wrote:
>
> Hi Arnaldo,
>
> When building a kernel with LLVM and CONFIG_DEBUG_INFO_BTF after commit
> 32ef9e5054ec ("Makefile.debug: re-enable debug info for .S files") in
> the kernel, I see the following spew of warnings, which appear to come
> from pahole:
>
> $ clang --version
> clang version 15.0.0 (Fedora 15.0.0-3.fc38)
> Target: x86_64-redhat-linux-gnu
> Thread model: posix
> InstalledDir: /usr/bin
>
> $ pahole --version
> v1.24
>
> $ make -skj"$(nproc)" ARCH=x86_64 LLVM=1 defconfig
>
> $ scripts/config \
> -d DEBUG_INFO_NONE \
> -e BPF_SYSCALL \
> -e DEBUG_INFO_BTF \
> -e DEBUG_INFO_DWARF5
>
> $ make -skj"$(nproc)" ARCH=x86_64 LLVM=1 olddefconfig all
> ...
> die__process_unit: DW_TAG_label (0xa) @ <0x7b> not handled!
> die__process_unit: tag not supported 0xa (label)!
> die__process_unit: DW_TAG_label (0xa) @ <0x97> not handled!
> die__process_unit: DW_TAG_label (0xa) @ <0xbd> not handled!
> die__process_unit: DW_TAG_label (0xa) @ <0xed> not handled!
> die__process_unit: DW_TAG_label (0xa) @ <0x109> not handled!
> die__process_unit: DW_TAG_label (0xa) @ <0x12a> not handled!
> die__process_unit: DW_TAG_label (0xa) @ <0x146> not handled!
> die__process_unit: DW_TAG_label (0xa) @ <0x16f> not handled!
Running llvm-dwarfdump on vmlinux, I see:
```
$ make -skj"$(nproc)" ARCH=x86_64 LLVM=1 olddefconfig all
die__process_unit: DW_TAG_label (0xa) @ <0xbf> not handled!
die__process_unit: tag not supported 0xa (label)!
...
$ llvm-dwarfdump vmlinux | less
...
0x000000bf: DW_TAG_label
DW_AT_name ("startup_64")
DW_AT_decl_file
("/android0/kernel-all/arch/x86/kernel/head_64.S")
DW_AT_decl_line (868)
DW_AT_low_pc (0xffffffff81000000)
0x000000db: DW_TAG_label
DW_AT_name ("secondary_startup_64")
DW_AT_decl_file
("/android0/kernel-all/arch/x86/kernel/head_64.S")
DW_AT_decl_line (921)
DW_AT_low_pc (0xffffffff81000060)
...
```
So these seem to be labels in assembler sources. The DW_TAGs look the
same to be for labels from C sources.
> ...
>
> Is this a problem with LLVM or pahole? I do not see this when building
> with GCC + GNU as but that could just be a red herring. I assume that
> there could be something missing for processing debug info from
> assembly, perhaps?
That's what I suspect.
> If there is any further information I can provide or
> anything I can test, I am more than happy to do so.
>
> Cheers,
> Nathan
I swear I used to be able to build pahole from sources...just moved to
a new machine and something seems off...
$ sudo apt install libdwarf-dev libdw-dev
$ git clone git://git.kernel.org/pub/scm/devel/pahole/pahole.git
$ mkdir pahole/build
$ cd !$
$ cmake -D__LIB=lib ..
$ make
...
[ 63%] Linking C executable codiff
/usr/bin/ld: libdwarves.so.1.0.0: undefined reference to `dwfl_module_getelf'
/usr/bin/ld: libdwarves.so.1.0.0: undefined reference to `dwfl_report_end'
...
--
Thanks,
~Nick Desaulniers
