LLVM-IFS(1)

📦
version 23.1.4 · 9 versions
, in arch rolling

💖 LLVM-IFS(1) — the shared object stubbing tool, explained by your fav ✨

okay so bestie, you know how llvm-ifs lives over in LLVM land and nobody ever explains it nicely? that's literally what this page is for 🫶 it's llvm-ifs(1), and by the end of this you're gonna be obsessed.

🌸 NAME 🌸

llvm-ifs — the shared object stubbing tool. yep. that's the whole vibe. it stubs. it's iconic. periodt 💅

✨ SYNOPSIS ✨

llvm-ifs [options] inputs

that's it. options on the left, your inputs on the right, go off 👑

🦋 DESCRIPTION 🦋

so like. llvm-ifs is a tool that jointly produces two things:

  • human-readable, text-based stubs — the .ifs files 💖
  • linkable shared object stubs — the .so files 🎀

and it makes them from either ELF shared objects or text-based stubs. main character energy, honestly — it reads both directions.

the text-based stubs are useful for monitoring ABI changes of the shared object, no cap 👀. and the linkable shared object stubs? those are how you avoid unnecessary relinks when the ABI of shared libraries does not change. so your build system doesn't have a whole meltdown over nothing. we love a queen who saves us from pointless rebuilds 🧚

🌈 IFS FORMATS 🌈

here's an example of the text representation (IFS) of a shared object, produced by llvm-ifs. screenshot it, save it, put it on your wall 🖼️:

--- !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 }
...

now let's break down every field, because each one is serving 💅

  • IFSVersion — the version of the IFS file, for reader compatibility. iykyk.
  • SoName (optional) — the name of the shared object file that's being stubbed.
  • Target (optional) — the architecture, endianness and bitwise information of this shared object. it can be in explicit format or in implicit LLVM triple format. it's optional, and it can be overridden from command line options. flexible queen ✨
  • NeededLibs — the list of the external shared objects that this library depends on. her support system 🫶
  • Symbols — a collection of all data needed to link objects for each symbol, sorted by name in ascending order. organized. unlike my room.
    • Name — symbol name.
    • Type — whether the symbol is an object, function, no-type, thread local storage, or unknown. symbol types that aren't explicitly supported get mapped as unknown, to improve signal-to-noise ratio. not me filtering the noise 💀
    • Size — the size of the symbol in question. doesn't apply to functions, and it's 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. a lil heads-up, a lil "bestie are you sure" 🔥

this YAML-based text format contains everything that's needed to generate a linkable ELF shared object as well as an Apple TAPI format file. and because the ordering of symbols is sorted, these files can be easily compared using diff tools 👑

if the content of the file changes, it indicates a potentially ABI breaking change 😭 so like, watch that diff. seriously.

🎀 ELF STUB FORMAT 🎀

a minimum ELF file that can be used by a linker should have the 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)
⚠️ heads up bestie: 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. so it's giving minimalist, not broken 💅

💜 OPTIONS 💜

every single one, no skips, no skipsies:

  • --input-format=[IFS|ELF|OtherObjectFileFormats] — specify the input file format. currently, only text IFS files and ELF shared object files are supported. this flag is optional, since the input format can be inferred. she reads the room 😌
  • --output-elf=<output-filename> — specify the output file for the ELF shared object stub.
  • --output-ifs=<output-filename> — specify the output file for the text IFS.
  • --output-tbd=<output-filename> — specify the output file for the Apple TAPI tbd.
  • --arch=[x86_64|AArch64|...] — 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 the ELF e_machine field. if the value conflicts with the IFS file, an error will be reported and the program will stop. no notes, she's done 🛑
  • --endianness=[little|big] — 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 conflicts with the IFS file, an error will be reported and the program will stop. pick a lane, bestie.
  • --bitwidth=[32|64] — 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 conflicts with the input IFS file, an error will be reported and the program will stop. 32 or 64, there is no 96 😭
  • --target=<target triple> — 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 an llvm target triple ✨ this flag cannot be used simultaneously with other target related flags. one at a time, she's monogamous 💅
  • --hint-ifs-target=<target triple> — optional, and should only be used when reading an ELF shared object and generating an IFS file. by default, llvm-ifs will use the 'Arch, Endianness and BitWidth' fields to reflect the target information from the input object file. using this flag tells 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 🫶 (yes, "filed" — that's the original wording, we don't gatekeep typos here)
  • --hint-ifs-target — 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 — 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 — 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 — 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. queen of not touching files she doesn't need to touch 🧚
  • --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. lowkey a niche icon.

⭐ EXIT STATUS ⭐

if llvm-ifs succeeds, it will exit with 0. otherwise, if an error occurs, it will exit with a non-zero value. clean, simple, communicative. we stan a tool with healthy boundaries 💖

👑 Author 👑

maintained by the LLVM Team (https://llvm.org/). literal legends, fr fr.

2003-2026, LLVM Project

and that's the whole page bestie!! go stub something iconic 💅🦋

okay bye — this was LLVM-IFS(1), release 23, dated 2026-10-20, mwah 😘✨

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