ELF_FLAGDATA(3)

📦 version 15.1, in freebsd 14.5, freebsd 15.1, nixpkgs unstable

💅 ELF_FLAGDATA — the libelf flag-shuffling girlies 💅

okay so this is a page from the Library Functions Manual and it's literally about the elf_flag* girlies in the ELF Access Library (libelf, link with -lelf). bestie, these functions are your little flag remote controls 🎀

✨ SYNOPSIS ✨

#include <libelf.h>

unsigned int
elf_flagarhdr(Elf_Arhdr *arhdr, Elf_Cmd cmd, unsigned int flags);

unsigned int
elf_flagdata(Elf_Data *data, Elf_Cmd cmd, unsigned int flags);

unsigned int
elf_flagehdr(Elf *elf, Elf_Cmd cmd, unsigned int flags);

unsigned int
elf_flagelf(Elf *elf, Elf_Cmd cmd, unsigned int flags);

unsigned int
elf_flagphdr(Elf *elf, Elf_Cmd cmd, unsigned int flags);

unsigned int
elf_flagscn(Elf_Scn *scn, Elf_Cmd cmd, unsigned int flags);

unsigned int
elf_flagshdr(Elf_Scn *scn, Elf_Cmd cmd, unsigned int flags);

like, seven little functions, all matching, all iconic 👑

🌸 DESCRIPTION 🌸

So here's the vibe: these functions let you query, set, or reset flags on the data structures that hang out with an ELF file. flag goblin behaviour only 💜

The arguments arhdr, data, elf and scn are the data structures whose flags you're changing. Important though — these are not just any rando values, they should have come back from earlier calls to functions in the elf(3) API set:

and the best part? these values are allowed to be NULL to simplify error handling in your application code 🫶 so you can be a little lazy and it's legal.

The argument cmd may have the following values:

  • ELF_C_CLR — the argument flags specifies the flags to be cleared. bye bye flags 💨
  • ELF_C_SET — the argument flags specifies the flags to be set. hello flags ✨

And the argument flags is allowed to have the following flags set:

  • ELF_F_ARCHIVE — this flag is only valid with the elf_flagelf() API. it informs the library that the application desires to create an ar(1) archive. the argument elf should have been opened for writing using the ELF_C_WRITE command to function elf_begin().
  • ELF_F_ARCHIVE_SYSV — this flag is used in conjunction with the ELF_F_ARCHIVE flag to indicate that the library should create archives that conform to System V layout rules. the default is to create BSD style archives. (default behaviour is always the plot twist 😭)
  • ELF_F_DIRTY — mark the associated data structure as needing to be written back to the underlying file. a subsequent call to elf_update(3) will resynchronize the library's internal data structures.
  • ELF_F_LAYOUT — this flag is only valid with the elf_flagelf() API. it informs the library that the application will take responsibility for the layout of the file and that the library is not to insert any padding in between sections. you're the main character now, you handle the layout 💅
ngl this part matters: marking a given data structure as "dirty" affects all of its contained elements. so marking an ELF descriptor elf with elf_flagelf(elf, ELF_C_SET, ELF_F_DIRTY) means that the entire contents of the descriptor are "dirty". it's giving contagious ✨

And last but not least: using a value of zero for argument flags will return the current set of flags for the data structure being queried. zero equals "just show me what's there" 🔍

🦋 RETURN VALUES 🦋

These functions return the updated flags if successful, or zero if an error is detected. zero is the "something went wrong" number, not a mood 💀

🧚 COMPATIBILITY 🧚

Heads up bestie: the elf_flagarhdr() function and the ELF_F_ARCHIVE and ELF_F_ARCHIVE_SYSV flags are an extension to the elf(3) API. not standard, but iconic 🌈

💀 ERRORS 💀

These functions may fail with the following errors:

  • [ELF_E_ARGUMENT] — an unsupported value was used for the cmd argument.
  • [ELF_E_ARGUMENT] — argument flags had unsupported flags set.
  • [ELF_E_ARGUMENT] — the argument elf was not a descriptor for an ELF object.
  • [ELF_E_MODE] — the ELF_F_ARCHIVE flag was used with an ELF descriptor that had not been opened for writing.
  • [ELF_E_SEQUENCE] — function elf_flagehdr() was called without an executable header being allocated.
  • [ELF_E_SEQUENCE] — function elf_flagphdr() was called without a program header being allocated.
fr fr read those [ELF_E_SEQUENCE] ones — order of operations matters, don't be out here flagging headers that don't exist yet 😭🙈

🌟 SEE ALSO 🌟

elf(3), elf32_newehdr(3), elf32_newphdr(3), elf64_newehdr(3), elf64_newphdr(3), elf_newdata(3), elf_update(3), gelf(3), gelf_newehdr(3), gelf_newphdr(3), gelf_update_dyn(3), gelf_update_move(3), gelf_update_rel(3), gelf_update_rela(3), gelf_update_sym(3), gelf_update_syminfo(3)

the whole friend group, go say hi 🫶✨

mwah 💋 this page came from Debian, dated June 12, 2019 — shoutout to the Debian girlies for keeping the docs cute. go forth and flag responsibly, bestie 🎀💖

📦 where this page comes from