kernel/scripts/gendwarfksyms/dwarf.c, branch linux-rolling-stable

gendwarfksyms: Fix build on 32-bit hosts

2026-03-04T12:19:40Z

[ Upstream commit ddc54f912a551f6eb0bbcfc3880f45fe27a252cb ] We have interchangeably used unsigned long for some of the types defined in elfutils, assuming they're always 64-bit. This obviously fails when building gendwarfksyms on 32-bit hosts. Fix the types. Reported-by: Michal Suchánek Closes: https://lore.kernel.org/linux-modules/aRcxzPxtJblVSh1y@kitsune.suse.cz/ Tested-by: Michal Suchánek Signed-off-by: Sami Tolvanen Signed-off-by: Sasha Levin

gendwarfksyms: use preferred form of sizeof for allocation

2025-07-26T06:31:30Z

The preferred form is to use the variable being allocated to, rather than explicitly supplying a type name which might become stale. Also do this for memset. Suggested-by: Masahiro Yamada Signed-off-by: Giuliano Procida Reviewed-by: Sami Tolvanen Signed-off-by: Masahiro Yamada

gendwarfksyms: Add a kABI rule to override byte_size attributes

2025-05-25T09:12:22Z

A data structure can be partially opaque to modules if its allocation is handled by the core kernel, and modules only need to access some of its members. In this situation, it's possible to append new members to the structure without breaking the ABI, as long as the layout for the original members remains unchanged. For example, consider the following struct: struct s { unsigned long a; void *p; }; gendwarfksyms --stable --dump-dies produces the following type expansion: variable structure_type s { member base_type long unsigned int byte_size(8) encoding(7) a data_member_location(0) , member pointer_type { base_type void } byte_size(8) p data_member_location(8) } byte_size(16) To append new members, we can use the KABI_IGNORE() macro to hide them from gendwarfksyms --stable: struct s { /* old members with unchanged layout */ unsigned long a; void *p; /* new members not accessed by modules */ KABI_IGNORE(0, unsigned long n); }; However, we can't hide the fact that adding new members changes the struct size, as seen in the updated type string: variable structure_type s { member base_type long unsigned int byte_size(8) encoding(7) a data_member_location(0) , member pointer_type { base_type void } byte_size(8) p data_member_location(8) } byte_size(24) In order to support this use case, add a kABI rule that makes it possible to override the byte_size attribute for types: /* * struct s allocation is handled by the kernel, so * appending new members without changing the original * layout won't break the ABI. */ KABI_BYTE_SIZE(s, 16); This results in a type string that's unchanged from the original and therefore, won't change versions for symbols that reference the changed structure. Signed-off-by: Sami Tolvanen Reviewed-by: Petr Pavlu Signed-off-by: Masahiro Yamada

gendwarfksyms: Add a separate pass to resolve FQNs

2025-03-15T12:16:11Z

Using dwarf_getscopes_die to resolve fully-qualified names turns out to be rather slow, and also results in duplicate scopes being processed, which doesn't help. Simply adding an extra pass to resolve names for all DIEs before processing exports is noticeably faster. For the object files with the most exports in a defconfig+Rust build, the performance improvement is consistently >50%: rust/bindings.o: 1038 exports before: 9.5980 +- 0.0183 seconds time elapsed ( +- 0.19% ) after: 4.3116 +- 0.0287 seconds time elapsed ( +- 0.67% ) rust/core.o: 424 exports before: 5.3584 +- 0.0204 seconds time elapsed ( +- 0.38% ) after: 0.05348 +- 0.00129 seconds time elapsed ( +- 2.42% ) ^ Not a mistake. net/core/dev.o: 190 exports before: 9.0507 +- 0.0297 seconds time elapsed ( +- 0.33% ) after: 3.2882 +- 0.0165 seconds time elapsed ( +- 0.50% ) rust/kernel.o: 129 exports before: 6.8571 +- 0.0317 seconds time elapsed ( +- 0.46% ) after: 2.9096 +- 0.0316 seconds time elapsed ( +- 1.09% ) net/core/skbuff.o: 120 exports before: 5.4805 +- 0.0291 seconds time elapsed ( +- 0.53% ) after: 2.0339 +- 0.0231 seconds time elapsed ( +- 1.14% ) drivers/gpu/drm/display/drm_dp_helper.o: 101 exports before: 1.7877 +- 0.0187 seconds time elapsed ( +- 1.05% ) after: 0.69245 +- 0.00994 seconds time elapsed ( +- 1.44% ) net/core/sock.o: 97 exports before: 5.8327 +- 0.0653 seconds time elapsed ( +- 1.12% ) after: 2.0784 +- 0.0291 seconds time elapsed ( +- 1.40% ) drivers/net/phy/phy_device.o: 95 exports before: 3.0671 +- 0.0371 seconds time elapsed ( +- 1.21% ) after: 1.2127 +- 0.0207 seconds time elapsed ( +- 1.70% ) drivers/pci/pci.o: 93 exports before: 1.1130 +- 0.0113 seconds time elapsed ( +- 1.01% ) after: 0.4848 +- 0.0127 seconds time elapsed ( +- 2.63% ) kernel/sched/core.o: 83 exports before: 3.5092 +- 0.0223 seconds time elapsed ( +- 0.64% ) after: 1.1231 +- 0.0145 seconds time elapsed ( +- 1.29% ) Overall, a defconfig+DWARF5 build with gendwarfksyms and Rust is 14.8% faster with this patch applied on my test system. Without Rust, there's still a 10.4% improvement in build time when gendwarfksyms is used. Note that symbol versions are unchanged with this patch. Suggested-by: Giuliano Procida Signed-off-by: Sami Tolvanen Signed-off-by: Masahiro Yamada

gendwarfksyms: Add support for symbol type pointers

2025-01-10T16:25:26Z

The compiler may choose not to emit type information in DWARF for external symbols. Clang, for example, does this for symbols not defined in the current TU. To provide a way to work around this issue, add support for __gendwarfksyms_ptr_ pointers that force the compiler to emit the necessary type information in DWARF also for the missing symbols. Example usage: #define GENDWARFKSYMS_PTR(sym) \ static typeof(sym) *__gendwarfksyms_ptr_##sym __used \ __section(".discard.gendwarfksyms") = &sym; extern int external_symbol(void); GENDWARFKSYMS_PTR(external_symbol); Signed-off-by: Sami Tolvanen Reviewed-by: Petr Pavlu Signed-off-by: Masahiro Yamada

gendwarfksyms: Add support for reserved and ignored fields

2025-01-10T16:25:26Z

Distributions that want to maintain a stable kABI need the ability to make ABI compatible changes to kernel data structures 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. Change union processing to recognize field name prefixes that allow the user to ignore the union completely during symbol versioning with a __kabi_ignored prefix in a field name, or to replace the type of a placeholder field using a __kabi_reserved field name prefix. For example, assume we want to add a new field to an existing alignment hole in a data structure, and ignore the new field when calculating symbol versions: struct struct1 { int a; /* a 4-byte alignment hole */ unsigned long b; }; To add `int n` to the alignment hole, we can add a union that includes a __kabi_ignored field that causes gendwarfksyms to ignore the entire union: struct struct1 { int a; union { char __kabi_ignored_0; int n; }; unsigned long b; }; With --stable, both structs produce the same symbol version. Alternatively, when a distribution expects future modification to a data structure, they can explicitly add reserved fields: struct struct2 { long a; long __kabi_reserved_0; /* reserved for future use */ }; To take the field into use, we can again replace it with a union, with one of the fields keeping the __kabi_reserved name prefix to indicate the original type: struct struct2 { long a; union { long __kabi_reserved_0; struct { int b; int v; }; }; Here gendwarfksyms --stable replaces the union with the type of the placeholder field when calculating versions. Signed-off-by: Sami Tolvanen Reviewed-by: Petr Pavlu Signed-off-by: Masahiro Yamada

gendwarfksyms: Add support for kABI rules

2025-01-10T16:25:26Z

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 Signed-off-by: Masahiro Yamada

gendwarfksyms: Add symbol versioning

2025-01-10T16:25:25Z

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 Reviewed-by: Petr Pavlu Signed-off-by: Masahiro Yamada

gendwarfksyms: Add symtypes output

2025-01-10T16:25:25Z

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' 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 Reviewed-by: Petr Pavlu Signed-off-by: Masahiro Yamada

gendwarfksyms: Add die_map debugging

2025-01-10T16:25:25Z

Debugging the DWARF processing can be somewhat challenging, so add more detailed debugging output for die_map operations. Add the --dump-die-map flag, which adds color coded tags to the output for die_map changes. Signed-off-by: Sami Tolvanen Reviewed-by: Petr Pavlu Signed-off-by: Masahiro Yamada