Hi. Le samedi 2 septembre 2023, 09:40:46 CEST Alessandro Carminati a écrit : > Il giorno sab 2 set 2023 alle ore 08:36 Masahiro Yamada > > <masahiroy@xxxxxxxxxx> ha scritto: > > On Mon, Aug 28, 2023 at 8:45 PM Alessandro Carminati (Red Hat) > > > > <alessandro.carminati@xxxxxxxxx> wrote: > > > From: Alessandro Carminati <alessandro.carminati@xxxxxxxxx> > > > > > > It is not uncommon for drivers or modules related to similar peripherals > > > to have symbols with the exact same name. > > > While this is not a problem for the kernel's binary itself, it becomes > > > an > > > issue when attempting to trace or probe specific functions using > > > infrastructure like ftrace or kprobe. > > > > > > The tracing subsystem relies on the `nm -n vmlinux` output, which > > > provides > > > symbol information from the kernel's ELF binary. However, when multiple > > > symbols share the same name, the standard nm output does not > > > differentiate > > > between them. This can lead to confusion and difficulty when trying to > > > probe the intended symbol. > > > > > > ~ # cat /proc/kallsyms | grep " name_show" > > > ffffffff8c4f76d0 t name_show > > > ffffffff8c9cccb0 t name_show > > > ffffffff8cb0ac20 t name_show > > > ffffffff8cc728c0 t name_show > > > ffffffff8ce0efd0 t name_show > > > ffffffff8ce126c0 t name_show > > > ffffffff8ce1dd20 t name_show > > > ffffffff8ce24e70 t name_show > > > ffffffff8d1104c0 t name_show > > > ffffffff8d1fe480 t name_show > > > > > > **kas_alias** addresses this challenge by extending the symbol names > > > with > > > unique suffixes during the kernel build process. > > > The newly created aliases for these duplicated symbols are unique names > > > that can be fed to the ftracefs interface. By doing so, it enables > > > previously unreachable symbols to be probed. > > > > > > ~ # cat /proc/kallsyms | grep " name_show" > > > ffffffff974f76d0 t name_show > > > ffffffff974f76d0 t name_show__alias__6340 > > > ffffffff979cccb0 t name_show > > > ffffffff979cccb0 t name_show__alias__6341 > > > ffffffff97b0ac20 t name_show > > > ffffffff97b0ac20 t name_show__alias__6342 > > > ffffffff97c728c0 t name_show > > > ffffffff97c728c0 t name_show__alias__6343 > > > ffffffff97e0efd0 t name_show > > > ffffffff97e0efd0 t name_show__alias__6344 > > > ffffffff97e126c0 t name_show > > > ffffffff97e126c0 t name_show__alias__6345 > > > ffffffff97e1dd20 t name_show > > > ffffffff97e1dd20 t name_show__alias__6346 > > > ffffffff97e24e70 t name_show > > > ffffffff97e24e70 t name_show__alias__6347 > > > ffffffff981104c0 t name_show > > > ffffffff981104c0 t name_show__alias__6348 > > > ffffffff981fe480 t name_show > > > ffffffff981fe480 t name_show__alias__6349 > > > ~ # echo "p:kprobes/evnt1 name_show__alias__6349" \ > > > > > > > >/sys/kernel/tracing/kprobe_events > > > > > > ~ # cat /sys/kernel/tracing/kprobe_events > > > p:kprobes/evnt1 name_show__alias__6349 > > > > > > Changes from v1: > > > - Integrated changes requested by Masami to exclude symbols with > > > prefixes > > > > > > "_cfi" and "_pfx". > > > > > > - Introduced a small framework to handle patterns that need to be > > > excluded > > > > > > from the alias production. > > > > > > - Excluded other symbols using the framework. > > > - Introduced the ability to discriminate between text and data symbols. > > > - Added two new config symbols in this version: > > > CONFIG_KALLSYMS_ALIAS_DATA, > > > > > > which allows data for data, and CONFIG_KALLSYMS_ALIAS_DATA_ALL, which > > > excludes all filters and provides an alias for each duplicated symbol. > > > > > > https://lore.kernel.org/all/20230711151925.1092080-1-alessandro.carminat > > > i@xxxxxxxxx/ > > > > > > Changes from v2: > > > - Alias tags are created by querying DWARF information from the vmlinux. > > > - The filename + line number is normalized and appended to the original > > > name. - The tag begins with '@' to indicate the symbol source. > > > - Not a change, but worth mentioning, since the alias is added to the > > > existing> > > > > list, the old duplicated name is preserved, and the livepatch way of > > > dealing with duplicates is maintained. > > > > > > - Acknowledging the existence of scenarios where inlined functions > > > declared in> > > > > header files may result in multiple copies due to compiler behavior, > > > though > > > > > > it is not actionable as it does not pose an operational issue. > > > > > > - Highlighting a single exception where the same name refers to > > > different > > > > > > functions: the case of "compat_binfmt_elf.c," which directly includes > > > "binfmt_elf.c" producing identical function copies in two separate > > > modules. > > > > > > sample from new v3 > > > > > > ~ # cat /proc/kallsyms | grep gic_mask_irq > > > ffffd0b03c04dae4 t gic_mask_irq > > > ffffd0b03c04dae4 t gic_mask_irq@_drivers_irqchip_irq-gic_c_167 > > > ffffd0b03c050960 t gic_mask_irq > > > ffffd0b03c050960 t gic_mask_irq@_drivers_irqchip_irq-gic-v3_c_404 > > > ~ # > > > > > > https://lore.kernel.org/all/20230714150326.1152359-1-alessandro.carminat > > > i@xxxxxxxxx/ > > > > > > Signed-off-by: Alessandro Carminati (Red Hat) > > > <alessandro.carminati@xxxxxxxxx> --- > > > > > > init/Kconfig | 36 ++++ > > > scripts/Makefile | 4 + > > > scripts/kas_alias/Makefile | 4 + > > > scripts/kas_alias/a2l.c | 268 ++++++++++++++++++++++++++++ > > > scripts/kas_alias/a2l.h | 32 ++++ > > > scripts/kas_alias/duplicates_list.c | 70 ++++++++ > > > scripts/kas_alias/duplicates_list.h | 15 ++ > > > scripts/kas_alias/item_list.c | 230 ++++++++++++++++++++++++ > > > scripts/kas_alias/item_list.h | 26 +++ > > > scripts/kas_alias/kas_alias.c | 217 ++++++++++++++++++++++ > > > scripts/link-vmlinux.sh | 11 +- > > > 11 files changed, 910 insertions(+), 3 deletions(-) > > > > I added some review comments in another thread, but > > one of the biggest concerns might be "910 insertions". > > Based on the feedback I received in the reviews, I need to overhaul the > code, potentially reducing its size. What would be a reasonable number > of lines for this feature? > > > What this program does is quite simple, > > "find duplicated names, and call addr2line". > > > > You wrote a lot of code to self-implement these: > > - sort function > > - parse PATH env variable to find addr2line > > - fork addr2line to establish pipe communications > > Some of these functions might become obsolete in the upcoming v4, which > will certainly reduce the line count. > > > Have you considered writing the code in Python (or Perl)? > > Is it too slow? > > > >From my perspective, there is a concern that using Python or Perl might > > result in slower performance. My proficiency in Python and Perl is > limited, so I did not initially consider them as viable options for > implementing this solution. > > > Most of the functions you implemented are already > > available in script languages. > > > > > > > > I am not sure if "@<file-path>" is a good solution, > > but the amount of the added code looks too much to me. > > I had reservations about using the '@' symbol to decorate the alias because > it's not a character commonly found in the kallsyms output. However, after > careful consideration, I arrived at the conclusion that it was suitable for > the task because it would make the alias stand-out and be easily > identifiable. > I'm open to any suggestions or alternative approaches you may have on this > matter. I am maybe over-engineering the thing, but maybe we can have a CONFIG_KALLSYMS_ALIAS_FORMAT which users would set to indicate how to differentiate between two symbols? For example, CONFIG_KALLSYMS_ALIAS_FORMAT=@file-lineno would lead to what we have currently. If you switch to using a higher level language, you can maybe focus more on this. Anyway, I personally like what this contribution offers currently as it permits to distinguish between same symbols. I will take a look at v4! Thank you again for working on this. > > -- > > Best Regards > > Masahiro Yamada > > Thank you Best regards.
