Message-ID: <CAEg-Je_wRvSiDLMXRpL+xaun3FjmfSmaYhZZbDn-nsEHg_A=dQ@mail.gmail.com>
Date: Sat, 28 Sep 2024 17:46:24 -0400
From: Neal Gompa <neal@...pa.dev>
To: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Masahiro Yamada <masahiroy@...nel.org>, Luis Chamberlain <mcgrof@...nel.org>, 
	Miguel Ojeda <ojeda@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Matthew Maurer <mmaurer@...gle.com>, Alex Gaynor <alex.gaynor@...il.com>, 
	Wedson Almeida Filho <wedsonaf@...il.com>, Gary Guo <gary@...yguo.net>, Petr Pavlu <petr.pavlu@...e.com>, 
	Hector Martin <marcan@...can.st>, Janne Grunau <j@...nau.net>, Miroslav Benes <mbenes@...e.cz>, 
	Asahi Linux <asahi@...ts.linux.dev>, linux-kbuild@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-modules@...r.kernel.org, 
	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v3 00/20] Implement DWARF modversions

On Mon, Sep 23, 2024 at 2:19 PM Sami Tolvanen <samitolvanen@...gle.com> wrote:
>
> Hi,
>
> Here's v3 of the DWARF modversions series [1][2]. The main
> motivation remains modversions support for Rust, which is important
> for distributions like Android that are eager to ship Rust kernel
> modules. Per Luis' request [3], v2 dropped the Rust specific bits
> from the series and instead added the feature as an option for
> the entire kernel. Matt is still addressing Rust modversion_info
> compatibility issues in a separate series [4], and we'll follow up
> with a patch to actually allow CONFIG_MODVERSIONS with Rust once
> everything else has been sorted out.
>
> A short background recap: Unlike C, Rust source code doesn't
> have sufficient information about the final ABI, as the compiler
> has considerable freedom in adjusting structure layout, for
> example, which makes using a source code parser like genksyms a
> non-starter. Based on Matt's suggestion and previous feedback from
> maintainers, this series uses DWARF debugging information for
> computing versions. DWARF is an established and a relatively stable
> format, which includes all the necessary ABI details, and adding a
> CONFIG_DEBUG_INFO dependency for Rust symbol versioning seems like a
> reasonable trade-off.
>
> The first two patches add more list macros to scripts/include and
> move the genksyms CRC32 implementation to a shared header file. The
> next 15 patches add gendwarfksyms, a tool for computing symbol
> versions from DWARF. When passed a list of exported symbols and
> object files, the tool generates an expanded type string for each
> symbol and computes symbol CRCs similarly to genksyms. gendwarfksyms
> is written in C and uses libdw to process DWARF. Patch 18 ensures
> that debugging information is present where we need it, patch 19
> adds gendwarfksyms as an alternative to genksyms, and the last patch
> adds documentation.
>
> Note that v3 is based on next-20240923 as it depends on Masahiro's
> scripts/include changes. For x86, we also need a separate small
> patch to include asm/ptrace.h in asm/ftrace.h. [5] For your
> convenience, you can find this series with all the prerequisites
> here:
>
> https://github.com/samitolvanen/linux/commits/gendwarfksyms-v3
>
> If you also want to test the series with Rust modules, this branch
> adds Matt's modversion_info series and a small patch to enable Rust
> modversions:
>
> https://github.com/samitolvanen/linux/commits/rustmodversions-v3
>
> Looking forward to hearing your thoughts!
>
> Sami
>
>
> [1] v1: https://lore.kernel.org/lkml/20240617175818.58219-17-samitolvanen@google.com/
> [2] v2: https://lore.kernel.org/lkml/20240815173903.4172139-21-samitolvanen@google.com/
> [3] https://lore.kernel.org/lkml/ZnIZEtkkQWEIGf9n@bombadil.infradead.org/
> [4] https://lore.kernel.org/lkml/20240806212106.617164-1-mmaurer@google.com/
> [5] https://lore.kernel.org/lkml/20240916221557.846853-2-samitolvanen@google.com/
>
> ---
>
> Changes in v3:
> - Updated SPX license headers.
>
> - Squashed the first two patches in v2 and tried to reduce churn as
>   much as reasonable.
>
> - Dropped patch 18 from v2 ("x86/asm-prototypes: Include
>   <asm/ptrace.h>") as it's addressed by a separate patch. [5]
>
> - Changed the error handling code to immediately terminate instead
>   of propagating the errors back to main, which cleaned up the code
>   quite a bit.
>
> - Switched to the list and hashtable implementations in scripts and
>   dropped the remaining tools/include dependencies. Added a couple
>   missing list macros. (patch 1)
>
> - Moved the genksyms CRC32 implementation to scripts/include and
>   dropped the duplicate code. (patches 2 and 14)
>
> - Switched from ad-hoc command line parsing to getopt_long (patch 3).
>
> - Added structure member and function parameter names to the DIE
>   output to match genksyms behavior, and tweaked the symtypes format
>   to be more parser-friendly in general based on Petr's suggestions.
>
> - Replaced the declaration-only struct annotations with more generic
>   kABI stability rules that allow source code annotations to be used
>   where #ifndef __GENKSYMS__ was previously used.  Added support for
>   rules that can be used to exclude enumerators from versioning.
>   (patch 16)
>
> - Per Miroslav's suggestion, added an option to hide structure
>   members from versioning when they're added to existing alignment
>   holes, for example. (patch 16)
>
> - Per Greg's request, added documentation and example macros for the
>   --stable features, and a couple of test cases. (patches 15, 16, and
>   20)
>
> - Fixed making symtypes files, which need to depend on .o files with
>   gendwarfksyms. (patch 19)
>
> - Addressed several other smaller issues that Petr and Masahiro
>   kindly pointed out during the v2 review.
>
> Changes in v2:
> - Per Luis' request, dropped Rust-specific patches and added
>   gendwarfksyms as an alternative to genksyms for the entire
>   kernel.
>
> - Added support for missing DWARF features needed to handle
>   also non-Rust code.
>
> - Changed symbol address matching to use the symbol table
>   information instead of relying on addresses in DWARF.
>
> - Added __gendwarfksyms_ptr patches to ensure the compiler emits
>   the necessary type information in DWARF even for symbols that
>   are defined in other TUs.
>
> - Refactored debugging output and moved the more verbose output
>   behind --dump* flags.
>
> - Added a --symtypes flag for generating a genksyms-style
>   symtypes output based on Petr's feedback, and refactored
>   symbol version calculations to be based on symtypes instead
>   of raw --dump-dies output.
>
> - Based on feedback from Greg and Petr, added --stable flag and
>   support for reserved data structure fields and declaration-onl
>   structures. Also added examples for using these features.
>
> - Added a GENDWARFKSYMS option and hooked up kbuild support
>   for both C and assembly code. Note that with gendwarfksyms,
>   we have to actually build a temporary .o file for calculating
>   assembly modversions.
>
> ---
>
> Sami Tolvanen (20):
>   scripts: import more list macros
>   scripts: move genksyms crc32 implementation to a common include
>   tools: Add gendwarfksyms
>   gendwarfksyms: Add address matching
>   gendwarfksyms: Expand base_type
>   gendwarfksyms: Add a cache for processed DIEs
>   gendwarfksyms: Expand type modifiers and typedefs
>   gendwarfksyms: Expand subroutine_type
>   gendwarfksyms: Expand array_type
>   gendwarfksyms: Expand structure types
>   gendwarfksyms: Limit structure expansion
>   gendwarfksyms: Add die_map debugging
>   gendwarfksyms: Add symtypes output
>   gendwarfksyms: Add symbol versioning
>   gendwarfksyms: Add support for kABI rules
>   gendwarfksyms: Add support for reserved and ignored fields
>   gendwarfksyms: Add support for symbol type pointers
>   export: Add __gendwarfksyms_ptr_ references to exported symbols
>   kbuild: Add gendwarfksyms as an alternative to genksyms
>   Documentation/kbuild: Add DWARF module versioning
>
>  Documentation/kbuild/gendwarfksyms.rst      |  274 +++++
>  Documentation/kbuild/index.rst              |    1 +
>  include/linux/export.h                      |   15 +
>  kernel/module/Kconfig                       |   31 +
>  scripts/Makefile                            |    3 +-
>  scripts/Makefile.build                      |   39 +-
>  scripts/gendwarfksyms/.gitignore            |    2 +
>  scripts/gendwarfksyms/Makefile              |   12 +
>  scripts/gendwarfksyms/cache.c               |   44 +
>  scripts/gendwarfksyms/die.c                 |  166 +++
>  scripts/gendwarfksyms/dwarf.c               | 1085 +++++++++++++++++++
>  scripts/gendwarfksyms/examples/kabi.h       |  141 +++
>  scripts/gendwarfksyms/examples/kabi_ex0.c   |   86 ++
>  scripts/gendwarfksyms/examples/kabi_ex1.c   |   89 ++
>  scripts/gendwarfksyms/examples/kabi_ex2.c   |   98 ++
>  scripts/gendwarfksyms/examples/kabi_rules.c |   56 +
>  scripts/gendwarfksyms/examples/symbolptr.c  |   29 +
>  scripts/gendwarfksyms/gendwarfksyms.c       |  195 ++++
>  scripts/gendwarfksyms/gendwarfksyms.h       |  351 ++++++
>  scripts/gendwarfksyms/kabi.c                |  214 ++++
>  scripts/gendwarfksyms/symbols.c             |  317 ++++++
>  scripts/gendwarfksyms/types.c               |  477 ++++++++
>  scripts/genksyms/genksyms.c                 |   77 +-
>  scripts/include/crc32.h                     |   93 ++
>  scripts/include/list.h                      |   50 +
>  25 files changed, 3860 insertions(+), 85 deletions(-)
>  create mode 100644 Documentation/kbuild/gendwarfksyms.rst
>  create mode 100644 scripts/gendwarfksyms/.gitignore
>  create mode 100644 scripts/gendwarfksyms/Makefile
>  create mode 100644 scripts/gendwarfksyms/cache.c
>  create mode 100644 scripts/gendwarfksyms/die.c
>  create mode 100644 scripts/gendwarfksyms/dwarf.c
>  create mode 100644 scripts/gendwarfksyms/examples/kabi.h
>  create mode 100644 scripts/gendwarfksyms/examples/kabi_ex0.c
>  create mode 100644 scripts/gendwarfksyms/examples/kabi_ex1.c
>  create mode 100644 scripts/gendwarfksyms/examples/kabi_ex2.c
>  create mode 100644 scripts/gendwarfksyms/examples/kabi_rules.c
>  create mode 100644 scripts/gendwarfksyms/examples/symbolptr.c
>  create mode 100644 scripts/gendwarfksyms/gendwarfksyms.c
>  create mode 100644 scripts/gendwarfksyms/gendwarfksyms.h
>  create mode 100644 scripts/gendwarfksyms/kabi.c
>  create mode 100644 scripts/gendwarfksyms/symbols.c
>  create mode 100644 scripts/gendwarfksyms/types.c
>  create mode 100644 scripts/include/crc32.h
>
>
> base-commit: ef545bc03a65438cabe87beb1b9a15b0ffcb6ace
> --
> 2.46.0.792.g87dc391469-goog
>

This patch set looks fairly reasonable.

Acked-by: Neal Gompa <neal@...pa.dev>



-- 
真実はいつも一つ！/ Always, there's only one truth!

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