DWARF_GET_WEAKS(3)

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

✨ DWARF_GET_WEAKS 💅

okay bestie, so this is a page from the Library Functions Manual — it's DWARF_GET_WEAKS(3), and yes the title is in all caps because it's that girl. We're talking libdwarf, we're talking weak symbols, we're talking the SGI-specific ".debug_weaknames" section. Buckle up 🎀

🌸 NAME 🌸

dwarf_get_weaks, dwarf_weak_cu_offset, dwarf_weak_die_offset, dwarf_weak_name_offsets, dwarf_weakname — the whole squad that retrieves information about weak symbols 🫶

🦋 LIBRARY 🦋

DWARF Access Library (libdwarf, -ldwarf) — like, that's the house these functions live in, no cap.

⭐ SYNOPSIS ⭐

#include <libdwarf.h>

int
dwarf_get_weaks(Dwarf_Debug dbg, Dwarf_Weak **weaks,
    Dwarf_Signed *nweaks, Dwarf_Error *err);

int
dwarf_weak_cu_offset(Dwarf_Weak weak, Dwarf_Off *cu_offset,
    Dwarf_Error *err);

int
dwarf_weak_die_offset(Dwarf_Weak weak, Dwarf_Off *die_offset,
    Dwarf_Error *err);

int
dwarf_weak_name_offsets(Dwarf_Weak weak, char **name,
    Dwarf_Off *die_offset, Dwarf_Off *cu_die_offset, Dwarf_Error *err);

int
dwarf_weakname(Dwarf_Weak weak, char **name, Dwarf_Error *err);

💖 DESCRIPTION 💖

So these functions pull info about weak symbols out of the lookup tables in the (SGI-specific) ".debug_weaknames" section. And the way they hand you that info? Through opaque descriptors of type Dwarf_Weak — very mysterious, very main character energy 💅. You can't just peek inside them, bestie; applications need to use the functions described below to retrieve the name and offset information contained in these descriptors.

dwarf_get_weaks() retrieves descriptors for all the weak symbols associated with the DWARF debug context specified by argument dbg. The argument weaks should point to a location that will be set to a pointer to an array of Dwarf_Weak descriptors. And the argument nweaks? That should point to a location that will be set to the number of descriptors returned. Two outputs, one call, we love efficiency ✨

dwarf_weak_cu_offset() returns the offset, relative to the ".debug_info" section, of the compilation unit that contains the debugging information entry associated with the argument weak. Argument cu_offset should point to a location that will hold the returned offset. Slay.

dwarf_weak_die_offset() retrieves the offset, relative to the ".debug_info" section, of the debugging information entry associated with the argument weak, and stores it into the location pointed to by the argument die_offset. Same vibe, different offset 💀

dwarf_weak_name_offsets() is the overachiever — it retrieves both the name and offsets for the debugging information entry for argument weak. Let's break it down, because there's a lot going on:

  • Argument name should point to a location which will be set to a pointer to a NUL-terminated string containing the name of the associated debugging information entry.
  • Argument die_offset should point to a location which will be set to the offset, relative to the ".debug_info" section, of the associated debugging information entry.
  • Argument cu_die_offset should point to a location which will be set to the offset, relative to the ".debug_info" section, of the first debugging information entry in the compilation unit associated with argument weak.

dwarf_weakname() sets the location pointed to by argument name to a pointer to a NUL-terminated string holding the name of the debugging information entry associated with the argument weak. Simple, cute, does exactly one thing 🎀

🧚 Memory Management 🧚

okay this part is important so listen up 🙈

The memory area used for the array of Dwarf_Weak descriptors returned in argument weaks by function dwarf_get_weaks() is owned by the DWARF Access Library (libdwarf, -ldwarf). Application code should not attempt to directly free this pointer. Portable code should instead use the function dwarf_weaks_dealloc(3) to indicate that the memory area may be freed. Like, it's not yours, don't touch it, ask nicely through the proper API 😭

The memory area used for the string returned in the name argument to functions dwarf_weak_name_offsets() and dwarf_weakname() is owned by the DWARF Access Library (libdwarf, -ldwarf). Portable code should indicate that the memory area can be freed using the dwarf_dealloc(3) function. Different string, different dealloc function — iykyk.

💜 Error Returns 💜

If argument err is not NULL, these functions will use it to store error information, in case of an error. So if you pass NULL, you're on your own, bestie — no error tea for you 🍓

🌈 RETURN VALUES 🌈

On success, these functions returns DW_DLV_OK. (Yeah, the original says "functions returns" — we're keeping the lore.) In case of an error, they return DW_DLV_ERROR and set the argument err. Periodt.

🔥 ERRORS 🔥

These functions may fail with the following errors — vibe check failed, basically:

  • [DW_DLE_ARGUMENT] — One of the arguments cu_die_offset, cu_offset, dbg, die_offset, weak, weaks, name, or nweaks was NULL. You handed it a nothing-burger, it's not gonna work 💀
  • [DW_DLE_NO_ENTRY] — The DWARF debugging context referenced by argument dbg did not contain information about weak symbols. The tea was simply not there 😭

👑 SEE ALSO 👑

💀 real talk though: don't free the library's memory yourself. Use dwarf_weaks_dealloc(3) for the descriptor array and dwarf_dealloc(3) for the name strings. That's the whole warning, and it's giving "respect the ownership boundaries."

okay that's the whole page, bestie, you ate it up 🫶 this little icon came from Debian, dated April 10, 2011 — like, vintage but still iconic ✨🎀

📦 where this page comes from