ELF_BEGIN(3)

👑 ELF_BEGIN — okay bestie, let's open a file ✨

So this is elf_begin, section 3 of the Libelf Programmer's Manual, and it's literally the moment where your ELF file gets a handle, a little passport that says "yes, I'm in this now." 💅

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🌸 NAME 🌸

elf_begin — initialize an ELF descriptor. That's it, that's the job, and it slays at it. 🫶

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🎀 SYNOPSIS 🎀

#include <libelf.h>

Elf *elf_begin(int fildes, Elf_Cmd cmd, Elf *ref);

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💖 DESCRIPTION 💖

Okay so picture this: you've got an ELF file just sitting there, unbothered, minding its business. elf_begin is the function that walks up and says "hey, come with me." It initializes and returns a handle to an ELF file so you can use it with the elfutils libelf library and the related elfutils libraries like libdw. 🦋

That Elf descriptor you get back? You must release it with elf_end(3) when you're done. It's giving "borrowed my hoodie" energy — you gotta give it back. 🙈

And before you touch any libelf library, including elf_begin(3) itself, you must call elf_version(3) first. No cap. That's the vibe check you do before the party. ✨

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🌈 PARAMETERS 🌈

• fildes — a file descriptor pointing at an ELF object. It should be open for reading, and optionally for writing, depending on what you're tryna do. ⭐ Now, if ref is non-NULL, then fildes must either be -1 or be set to the same file descriptor as the one associated with ref. Like, they have to match, bestie, no third options. 💀
• cmd — the action you wanna perform. The common ones are:
  • ELF_C_NULL — returns a NULL pointer instead of initializing an ELF descriptor. It straight-up ignores ref. Not rude, just honest. 🧚
  • ELF_C_READ — opens an ELF descriptor for reading. The classic. 👑
  • ELF_C_WRITE — opens an ELF descriptor for writing. The descriptor initially refers to an empty file. Blank canvas, main character energy. 🎀
  • ELF_C_RDWR — opens an ELF descriptor for reading and writing. Why choose one. 🌸
  • ELF_C_READ_MMAP — opens an ELF descriptor for reading using mmap, if available. Now listen — the ELF_C_*_MMAP commands are an elfutils libelf extension and may not be available in other libelf implementations. ⚠️ Also: once the mmap size is set, attempts to extend the size may fail. So the ELF_C_*_MMAP commands tend to be more useful for in-place modifications or for removing data from an ELF descriptor. Basically: great for glow-ups in place, not for growing. 💅
  • ELF_C_WRITE_MMAP — opens an ELF descriptor for writing using mmap, if available. The descriptor initially refers to an empty file. ✨
  • ELF_C_RDWR_MMAP — opens an ELF descriptor for reading and writing using mmap, if available. 🔥
  • ELF_C_READ_MMAP_PRIVATE — opens an ELF descriptor for reading using mmap, if available. This one invokes mmap with MAP_PRIVATE, whereas the other ELF_C_*_MMAP commands invoke mmap with MAP_SHARED. Peep mmap(2) for the full tea. 🍓
• ref — a reference to an existing Elf descriptor. Here's where it gets interesting: 👀
  • If ref refers to a regular ELF binary (not an AR file), then elf_begin will duplicate ref. The reference count associated with ref will be incremented, and elf_end(3) will need to be called an additional time to deallocate ref. And ref must have been opened with read/write permissions consistent with cmd. Consistency is the moment. ✨
  • If ref refers to an AR file, then the ELF descriptor returned will be the first available object member of the archive. See elf_next(3) for more info. 📚
  • ref may be NULL, in which case this argument is simply ignored. Not me ghosting an argument. 💀

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🌟 RETURN VALUE 🌟

On success, elf_begin() returns a pointer to a new Elf descriptor. Periodt. 🫶

If cmd is ELF_C_NULL then NULL is returned. If ref is non-NULL and isn't an AR file, then a copy of ref is returned. And on failure, elf_begin() returns NULL and sets an internal error state that you can retrieve with elf_errmsg(3). So if it flops, it tells you why — you just have to ask. 😭

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👀 SEE ALSO 👀

mmap(2), elf_clone(3), elf_end(3), elf_next(3), elf_rand(3), libelf(3), elf(5)

The whole friend group. Go say hi. 🫶

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🦋 ATTRIBUTES 🦋

• Interface: elf_begin()
• Attribute: Thread safety
• Value: MT-Safe

She's MT-Safe, bestie. Multiple threads can hang out with her and nobody's fighting. 👑

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🚨 REPORTING BUGS 🚨

Found a bug? Don't suffer in silence, tell the devs! Report bugs to <elfutils-devel@sourceware.org> or hit up https://sourceware.org/bugzilla/. They wanna know. fr fr. 💜

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And that's the whole page, mwah 💋 — brought to you by Libelf, dated 2025-06-02, filed under ELF_BEGIN(3). Now go call elf_version(3) first, I'm begging you. 🎀✨