Re: [PATCH 20/20] symtab: Add support for MODVERSIONS (CRC checksums)

[Dodji Seketeli <dodji@seketeli.org>]

Matthias Maennich <maennich@google.com> a écrit:

> The Linux Kernel has a mechanism (MODVERSIONS) to checksum symbols based
> on their type. In a way similar to what libabigail does, but different.
> The CRC values for symbols can be extracted from the symtab either by
> following the __kcrctab_<symbol> entry or by using the __crc_<symbol>
> value directly.
>
> This patch adds support for extracting those CRC values and storing them
> as a property of elf_symbol. Subsequently, 'crc' gets emitted as an
> attribute of 'elf-symbol' in the XML representation.

This is pretty cool btw.

Personally, I would have tied the CRC to the decl instead of the ELF
symbol.  I know in the kernel land, symbols and decls are usually
thought of interchangeably but conceptually, they are not the same
thing.

The linux kernel CRCs are computed from the types of the declarations
that are associated to the ELF symbol.  I am talking about the genksyms
machinery.  Se we are really talking about the declarations and types
here.  They are storing in ELF because there is no concept of decls and
types in ELF.  But we do have that in libabigail.  So I really think it
makes more sense to have this tied to decls instead of ELF symbols.

If tomorrow we build or get a hash for decls and types we'll have to
re-do this again, at the decl level.

As a matter of fact, the feature already exists for type units in DWARF
for instance.  We just don't support that yet.  But we might have to
support it in the future.

So the more I think about this, the more I think we should add an
"artifact_hash" property to type_or_decl_base instead of putting this
into the ELF symbol.

What do you think?

[...]

Cheers,

-- 
		Dodji