Re: [PATCH v13 5/5] rust: Use gendwarfksyms + extended modversions for CONFIG_MODVERSIONS

Sami Tolvanen
2025-01-14T18:58:24Z

On Tue, Jan 14, 2025 at 10:22:15AM +0900, Masahiro Yamada wrote:
> On Tue, Jan 14, 2025 at 5:04 AM Sami Tolvanen <samitolvanen@google.com> wrote:
> >
> > Hi Masahiro,
> >
> > On Fri, Jan 10, 2025 at 6:26 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> > >
> > > On Sat, Jan 4, 2025 at 2:37 AM Matthew Maurer <mmaurer@google.com> wrote:
> > > >
> > > > From: Sami Tolvanen <samitolvanen@google.com>
> > > >
> > > > Previously, two things stopped Rust from using MODVERSIONS:
> > > > 1. Rust symbols are occasionally too long to be represented in the
> > > > original versions table
> > > > 2. Rust types cannot be properly hashed by the existing genksyms
> > > > approach because:
> > > > * Looking up type definitions in Rust is more complex than C
> > > > * Type layout is potentially dependent on the compiler in Rust,
> > > > not just the source type declaration.
> > > >
> > > > CONFIG_EXTENDED_MODVERSIONS addresses the first point, and
> > > > CONFIG_GENDWARFKSYMS the second. If Rust wants to use MODVERSIONS, allow
> > > > it to do so by selecting both features.
> > > >
> > > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> > > > Co-developed-by: Matthew Maurer <mmaurer@google.com>
> > > > Signed-off-by: Matthew Maurer <mmaurer@google.com>
> > > > ---
> > > > init/Kconfig | 3 ++-
> > > > rust/Makefile | 34 ++++++++++++++++++++++++++++++++--
> > > > 2 files changed, 34 insertions(+), 3 deletions(-)
> > > >
> > > > diff --git a/init/Kconfig b/init/Kconfig
> > > > index c1f9eb3d5f2e892e977ba1425599502dc830f552..b60acfd9431e0ac2bf401ecb6523b5104ad31150 100644
> > > > --- a/init/Kconfig
> > > > +++ b/init/Kconfig
> > > > @@ -1959,7 +1959,8 @@ config RUST
> > > > bool "Rust support"
> > > > depends on HAVE_RUST
> > > > depends on RUST_IS_AVAILABLE
> > > > - depends on !MODVERSIONS
> > > > + select EXTENDED_MODVERSIONS if MODVERSIONS
> > > > + depends on !MODVERSIONS || GENDWARFKSYMS
> > > > depends on !GCC_PLUGIN_RANDSTRUCT
> > > > depends on !RANDSTRUCT
> > > > depends on !DEBUG_INFO_BTF || PAHOLE_HAS_LANG_EXCLUDE
> > > > diff --git a/rust/Makefile b/rust/Makefile
> > > > index a40a3936126d603836e0ec9b42a1285916b60e45..80f970ad81f7989afe5ff2b5f633f50feb7f6006 100644
> > > > --- a/rust/Makefile
> > > > +++ b/rust/Makefile
> > > > @@ -329,10 +329,11 @@ $(obj)/bindings/bindings_helpers_generated.rs: private bindgen_target_extra = ;
> > > > $(obj)/bindings/bindings_helpers_generated.rs: $(src)/helpers/helpers.c FORCE
> > > > $(call if_changed_dep,bindgen)
> > > >
> > > > +rust_exports = $(NM) -p --defined-only $(1) | awk '$$2~/(T|R|D|B)/ && $$3!~/__cfi/ { printf $(2),$(3) }'
> > > > +
> > > > quiet_cmd_exports = EXPORTS $@
> > > > cmd_exports = \
> > > > - $(NM) -p --defined-only $< \
> > > > - | awk '$$2~/(T|R|D|B)/ && $$3!~/__cfi/ {printf "EXPORT_SYMBOL_RUST_GPL(%s);\n",$$3}' > $@
> > > > + $(call rust_exports,$<,"EXPORT_SYMBOL_RUST_GPL(%s);\n",$$3) > $@
> > >
> > > I noticed a nit:
> > >
> > > Both of the two callsites of rust_exports pass
> > > '$$3' to the last parameter instead of hardcoding it.
> > >
> > > Is it a flexibility for future extensions?
> > >
> > > I cannot think of any other use except for printing
> > > the third column, i.e. symbol name.
> >
> > Good catch, the last parameter isn't necessary anymore. It was used in
> > early versions of the series to also pass symbol addresses to
> > gendwarfksyms, but that's not needed since we read the symbol table
> > directly now.
>
> If you submit a diff, I will squash it to 5/5.
> (You do not need to input commit description body)

Thanks, here's a diff that drops the last parameter.

Sami

diff --git a/rust/Makefile b/rust/Makefile
index 80f970ad81f7..ab300bfb46f6 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -329,11 +329,11 @@ $(obj)/bindings/bindings_helpers_generated.rs: private bindgen_target_extra = ;
$(obj)/bindings/bindings_helpers_generated.rs: $(src)/helpers/helpers.c FORCE
$(call if_changed_dep,bindgen)

-rust_exports = $(NM) -p --defined-only $(1) | awk '$$2~/(T|R|D|B)/ && $$3!~/__cfi/ { printf $(2),$(3) }'
+rust_exports = $(NM) -p --defined-only $(1) | awk '$$2~/(T|R|D|B)/ && $$3!~/__cfi/ { printf $(2),$$3 }'

quiet_cmd_exports = EXPORTS $@
cmd_exports = \
- $(call rust_exports,$<,"EXPORT_SYMBOL_RUST_GPL(%s);\n",$$3) > $@
+ $(call rust_exports,$<,"EXPORT_SYMBOL_RUST_GPL(%s);\n") > $@

$(obj)/exports_core_generated.h: $(obj)/core.o FORCE
$(call if_changed,exports)
@@ -404,7 +404,7 @@ endif

ifdef CONFIG_MODVERSIONS
cmd_gendwarfksyms = $(if $(skip_gendwarfksyms),, \
- $(call rust_exports,$@,"%s\n",$$3) | \
+ $(call rust_exports,$@,"%s\n") | \
scripts/gendwarfksyms/gendwarfksyms \
$(if $(KBUILD_GENDWARFKSYMS_STABLE), --stable) \
$(if $(KBUILD_SYMTYPES), --symtypes $(@:.o=.symtypes),) \