Provided by: llvm-18_18.1.3-1ubuntu1_amd64 
NAME
llvm-ifs - shared object stubbing tool
SYNOPSIS
llvm-ifs [options] inputs
DESCRIPTION
llvm-ifs is a tool that jointly produces human readable text-based stubs (.ifs files) for shared objects
and linkable shared object stubs (.so files) from either ELF shared objects or text-based stubs. The
text-based stubs is useful for monitoring ABI changes of the shared object. The linkable shared object
stubs can be used to avoid unnecessary relinks when the ABI of shared libraries does not change.
IFS FORMATS
Here is an example of the text representation (IFS) of a shared object produced by the llvm-ifs:
--- !ifs-v1
IFSVersion: 3.0
SoName: libtest.so /* Optional */
Target: x86_64-unknown-linux-gnu /* Optional, format 1, same format as llvm target triple */
Target: { Arch: x86_64, Endianness: little, Bitwidth: 64 } /* Optional, format 2 */
NeededLibs:
- libc.so.6
Symbols:
- { Name: sym0, Type: Notype }
- { Name: sym1, Type: Object, Size: 0 }
- { Name: sym2, Type: Func, Weak: false }
- { Name: sym3, Type: TLS }
- { Name: sym4, Type: Unknown, Warning: foo }
...
• IFSVersion: Version of the IFS file for reader compatibility.
• SoName (optional): Name of the shared object file that is being stubbed.
• Target (optional): The architecture, endianness and bitwise information of this shared object. It can
be either in explicit format or in implicit LLVM triple format. It can be optional and can be
overridden from command line options.
• NeededLibs: The list of the external shared objects that this library depends on.
• Symbols: A collection of all data needed to link objects for each symbol, sorted by name in ascending
order.
• Name: Symbol name.
• Type: Whether the symbol is an object, function, no-type, thread local storage, or unknown. Symbol
types not explicitly supported are mapped as unknown to improve signal-to-noise ratio.
• Size: The size of the symbol in question, doesn't apply to functions, and is optional for NoType
symbols.
• Undefined: Whether or not the symbol is defined in this shared object file.
• Weak: Whether or not the symbol should be treated as weak.
• Warning (optional): Warning text to output when this symbol is linked against.
This YAML based text format contains everything that is needed to generate a linkable ELF shared object
as well as an Apple TAPI format file. The ordering of symbols is sorted, so these files can be easily
compared using diff tools. If the content of the file changes, it indicates a potentially ABI breaking
change.
ELF STUB FORMAT
A minimum ELF file that can be used by linker should have following sections properly populated:
• ELF header.
• Section headers.
• Dynamic symbol table (.dynsym section).
• Dynamic string table (.dynstr section).
• Dynamic table (.dynamic section).
• DT_SYMTAB entry.
• DT_STRTAB entry.
• DT_STRSZ entry.
• DT_NEEDED entries. (optional)
• DT_SONAME entry. (optional)
• Section header string table (.shstrtab section)
This ELF file may have compatibility issues with ELF analysis tools that rely on the program headers.
Linkers like LLD work fine with such a minimum ELF file without errors.
OPTIONS
--input-format=[IFS|ELF|OtherObjectFileFormats]
Specify input file format. Currently, only text IFS files and ELF shared object files are
supported. This flag is optional as the input format can be inferred.
--output-elf=<output-filename>
Specify the output file for ELF shared object stub.
--output-ifs=<output-filename>
Specify the output file for text IFS.
--output-tbd=<output-filename>
Specify the output file for Apple TAPI tbd.
--arch=[x86_64|AArch64|...]
This flag is optional and it should only be used when reading an IFS file which does not define
the Arch (architecture). This flag defines the architecture of the output file, and can be any
string supported by ELF 'e_machine' field. If the value is conflicting with the IFS file, an error
will be reported and the program will stop.
--endianness=[little|big]
This flag is optional and it should only be used when reading an IFS file which does not define
the Endianness. This flag defines the endianness of the output file. If the value is conflicting
with the IFS file, an error will be reported and the program will stop.
--bitwidth=[32|64]
This flag is optional and it should only be used when reading an IFS file which does not define
the BitWidth. This flag defines the bit width of the output file. If the value is conflicting with
the input IFS file, an error will be reported and the program will stop.
--target=<target triple>
This flag is optional and should only be used when reading an IFS file which does not define any
target information. This flag defines architecture, endianness and bit width of the output file
using llvm target triple. This flag cannot be used simultaneously with other target related
flags.
--hint-ifs-target=<target triple>
This flag is optional and should only be used when reading an ELF shared object and generating an
IFS file. by default, llvm-ifs will use 'Arch, Endianness and BitWidth' fields to reflect the
target information from the input object file. Using this flag will tell llvm-ifs the expected
target triple in the output IFS file. If the value matches the target information from the object
file, this value will be used in the 'Target:' filed in the generated IFS. If it conflicts with
the input object file, an error will be reported and the program will stop.
--hint-ifs-target
This flag is optional and should only be used when outputting an IFS file. This flag strips the
Arch field from the IFS file so it can be overridden later.
--strip-ifs-endianness
This flag is optional and should only be used when outputting an IFS file. This flag strips the
Endianness field from the IFS file so it can be overridden later.
--strip-ifs-bitwidth
This flag is optional and should only be used when outputting an IFS file. This flag strips the
BitWidth field from the IFS file so it can be overridden later.
--strip-ifs-target
This flag is optional and should only be used when outputting an IFS file. This flag strips the
Target field from the IFS file so it can be overridden later.
--write-if-changed
When this flag is set, llvm-ifs will only write the output file if it does not already exist or
the content will be different from the existing file.
--strip-size
When this flag is set, llvm-ifs will remove the size field from the output ifs file. This is
useful for shared objects that only intend to be linked against position independent code which
doesn't need copy relocations, or where the size of an object is not a useful part of the abi to
track.
EXIT STATUS
If llvm-ifs succeeds, it will exit with 0. Otherwise, if an error occurs, it will exit with a non-zero
value.
AUTHOR
Maintained by the LLVM Team (https://llvm.org/).
COPYRIGHT
2003-2024, LLVM Project
15 2024-05-27 LLVM-IFS(1)