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Distributions that want to maintain a stable kABI need the ability
to make ABI compatible changes to kernel without affecting symbol
versions, either because of LTS updates or backports.
With genksyms, developers would typically hide these changes from
version calculation with #ifndef __GENKSYMS__, which would result
in the symbol version not changing even though the actual type has
changed. When we process precompiled object files, this isn't an
option.
To support this use case, add a --stable command line flag that
gates kABI stability features that are not needed in mainline
kernels, but can be useful for distributions, and add support for
kABI rules, which can be used to restrict gendwarfksyms output.
The rules are specified as a set of null-terminated strings stored
in the .discard.gendwarfksyms.kabi_rules section. Each rule consists
of four strings as follows:
"version\0type\0target\0value"
The version string ensures the structure can be changed in a
backwards compatible way. The type string indicates the type of the
rule, and target and value strings contain rule-specific data.
Initially support two simple rules:
1. Declaration-only types
A type declaration can change into a full definition when
additional includes are pulled in to the TU, which changes the
versions of any symbol that references the type. Add support
for defining declaration-only types whose definition is not
expanded during versioning.
2. Ignored enumerators
It's possible to add new enum fields without changing the ABI,
but as the fields are included in symbol versioning, this would
change the versions. Add support for ignoring specific fields.
3. Overridden enumerator values
Add support for overriding enumerator values when calculating
versions. This may be needed when the last field of the enum
is used as a sentinel and new fields must be added before it.
Add examples for using the rules under the examples/ directory.
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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Calculate symbol versions from the fully expanded type strings in
type_map, and output the versions in a genksyms-compatible format.
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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Add support for producing genksyms-style symtypes files. Process
die_map to find the longest expansions for each type, and use symtypes
references in type definitions. The basic file format is similar to
genksyms, with two notable exceptions:
1. Type names with spaces (common with Rust) in references are
wrapped in single quotes. E.g.:
s#'core::result::Result<u8, core::num::error::ParseIntError>'
2. The actual type definition is the simple parsed DWARF format we
output with --dump-dies, not the preprocessed C-style format
genksyms produces.
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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Expand each structure type only once per exported symbol. This
is necessary to support self-referential structures, which would
otherwise result in infinite recursion, and it's sufficient for
catching ABI changes.
Types defined in .c files are opaque to external users and thus
cannot affect the ABI. Consider type definitions in .c files to
be declarations to prevent opaque types from changing symbol
versions.
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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Basic types in DWARF repeat frequently and traversing the DIEs using
libdw is relatively slow. Add a simple hashtable based cache for the
processed DIEs.
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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Add a basic DWARF parser, which uses libdw to traverse the debugging
information in an object file and looks for functions and variables.
In follow-up patches, this will be expanded to produce symbol versions
for CONFIG_MODVERSIONS from DWARF.
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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