As of Linux 5.3-rc4, there are 31203 [1] exported symbols in the kernel.
That is a growth of almost 1000 symbols since 4.17 (30206 [2]). There
seems to be some consensus amongst kernel devs that the export surface
is too large, and hard to reason about.
Generally, these symbols fall in one of these categories:
1) Symbols actually meant for drivers
2) Symbols that are only exported because functionality is split over
multiple modules, yet they really shouldn't be used by modules outside
of their own subsystem
3) Symbols really only meant for in-tree use
When module developers try to upstream their code, it regularly turns
out that they are using exported symbols that they really shouldn't be
using. This problem is even bigger for drivers that are currently
out-of-tree, which may be using many symbols that they shouldn't be
using, and that break when those symbols are removed or modified.
This patch allows subsystem maintainers to partition their exported
symbols into separate namespaces, and module authors to import such
namespaces only when needed.
This allows subsystem maintainers to more easily limit availability of
these namespaced symbols to other parts of the kernel. It can also be
used to partition the set of exported symbols for documentation
purposes; for example, a set of symbols that is really only used for
debugging could be in a "SUBSYSTEM_DEBUG" namespace.
I continued the work mainly done by Martijn Coenen. In this v2 the
following changes have been introduced compared to v1 of this series:
- Rather than adding and evaluating separate sections __knsimport_NS,
use modinfo tags to declare the namespaces a module introduces.
Adjust modpost and the module loader accordingly.
- Also add support for reading multiple modinfo values for the same tag
to allow list-like access to modinfo tags.
- The macros in export.h have been cleaned up to avoid redundancy in the
macro parameters (ns, nspost, nspost2).
- The introduction of relative references in the ksymtab entries caused
a rework of the macros to accommodate that configuration as well.
- Alignment of kernel_symbol in the ksymtab needed to be fixed to allow
growing the kernel_symbol struct.
- Modpost does now also append the namespace suffix to the symbol
entries in Module.symvers.
- The configuration option MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS allows
relaxing the enforcement of properly declared namespace imports at module
loading time.
- Symbols can be collectively exported into a namespace by defining
DEFAULT_SYMBOL_NAMESPACE in the corresponding Makefile.
- The requirement for a very recent coccinelle spatch has been lifted by
simplifying the script.
- nsdeps does now ensures MODULE_IMPORT_NS statements are sorted when
patching the module source files.
- Some minor bugs have been addressed in nsdeps to allow it to work with
modules that have more than one source file.
- The RFC for the usb-storage symbols has been simplified by using
DEFAULT_SYMBOL_NAMESPACE=USB_STORAGE rather than explicitly exporting each
and every symbol into that new namespace.
This patch series was developed against v5.3-rc4.
[1] git grep "^EXPORT_SYMBOL\w*(" v5.3-rc4 | wc -l
[2] git grep "^EXPORT_SYMBOL\w*(" v4.17 | wc -l
Matthias Maennich (10):
module: support reading multiple values per modinfo tag
export: explicitly align struct kernel_symbol
module: add support for symbol namespaces.
modpost: add support for symbol namespaces
module: add config option MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS
export: allow definition default namespaces in Makefiles or sources
modpost: add support for generating namespace dependencies
scripts: Coccinelle script for namespace dependencies.
usb-storage: remove single-use define for debugging
RFC: usb-storage: export symbols in USB_STORAGE namespace
MAINTAINERS | 5 +
Makefile | 12 ++
arch/m68k/include/asm/export.h | 1 -
drivers/usb/storage/Makefile | 2 +
drivers/usb/storage/alauda.c | 1 +
drivers/usb/storage/cypress_atacb.c | 1 +
drivers/usb/storage/datafab.c | 1 +
drivers/usb/storage/debug.h | 2 -
drivers/usb/storage/ene_ub6250.c | 1 +
drivers/usb/storage/freecom.c | 1 +
drivers/usb/storage/isd200.c | 1 +
drivers/usb/storage/jumpshot.c | 1 +
drivers/usb/storage/karma.c | 1 +
drivers/usb/storage/onetouch.c | 1 +
drivers/usb/storage/realtek_cr.c | 1 +
drivers/usb/storage/scsiglue.c | 2 +-
drivers/usb/storage/sddr09.c | 1 +
drivers/usb/storage/sddr55.c | 1 +
drivers/usb/storage/shuttle_usbat.c | 1 +
drivers/usb/storage/uas.c | 1 +
include/asm-generic/export.h | 14 +-
include/linux/export.h | 92 +++++++++++--
include/linux/module.h | 2 +
init/Kconfig | 14 ++
kernel/module.c | 67 ++++++++-
scripts/Makefile.modpost | 4 +-
scripts/coccinelle/misc/add_namespace.cocci | 23 ++++
scripts/mod/modpost.c | 144 ++++++++++++++++++--
scripts/mod/modpost.h | 9 ++
scripts/nsdeps | 54 ++++++++
30 files changed, 421 insertions(+), 40 deletions(-)
create mode 100644 scripts/coccinelle/misc/add_namespace.cocci
create mode 100644 scripts/nsdeps
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2.23.0.rc1.153.gdeed80330f-goog
