DWARF_OBJECT_INIT(3)

✨ DWARF_OBJECT_INIT — okay bestie, let's talk libdwarf 💅

So picture this: you're in the DWARF Access Library (that's libdwarf, link it with -ldwarf), and you want to spin up your very own Dwarf_Debug descriptor but with your custom file-reading methods. That's literally what this function does. No cap.

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🌸 SYNOPSIS 🌸

#include <libdwarf.h>

int
dwarf_object_init(Dwarf_Obj_Access_Interface *iface,
    Dwarf_Handler errhand, Dwarf_Ptr errarg, Dwarf_Debug *dbg,
    Dwarf_Error *err);

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🎀 DESCRIPTION 🎀

Okay so dwarf_object_init() does the absolute most: it allocates and hands you back a Dwarf_Debug instance that reads file content using application-supplied access methods. Like, you're the main character deciding how the files get read. Iconic.

The argument iface should point to a populated Dwarf_Obj_Access_Interface structure. The deets on what goes in that structure? Scroll down to the "Object Access Functions" section, bestie, it's all there.

The argument errhand should point to a function that gets called when there's an error. If this argument is NULL then a default error handling scheme is used instead. Wanna know the error handling schemes available? Check out dwarf(3), it's giving full lore.

The argument errarg gets passed straight to the error handler function that errhand points to. Cute, right? They're a little duo.

The argument dbg should point to a memory location that will be set to a reference to the returned Dwarf_Debug descriptor. That's where your new baby lives.

The argument err is used to return a Dwarf_Error descriptor in case of an error. Because sometimes things go wrong and we need the receipts.

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🦋 Object Access Functions 🦋

The data structures used to specify object access methods are defined in <libdwarf.h>. Let's break them down one by one.

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💜 Dwarf_Obj_Access_Interface

This structure bundles together a set of file access methods along with a pointer to application-private state. Like a little gift basket of access methods, honestly.

typedef struct {
        void *object;
        const Dwarf_Obj_Access_Methods *methods;
} Dwarf_Obj_Access_Interface;

• object — This field points to application-specific state that will be passed as the first parameter to the actual access object methods.
• methods — This structure contains pointers to the functions implementing the access methods, as described below. It's lowkey the whole point.

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🫶 Dwarf_Obj_Access_Methods

This structure specifies the functions implementing low-level access. It's giving "the crew that does the actual work."

typedef struct {
        int (*get_section_info)(void *obj, Dwarf_Half index,
            Dwarf_Obj_Access_Section *ret, int *error);
        Dwarf_Endianness (*get_byte_order)(void *obj);
        Dwarf_Small (*get_length_size)(void *obj);
        Dwarf_Small (*get_pointer_size)(void *obj);
        Dwarf_Unsigned (*get_section_count)(void *obj);
        int (*load_section)(void *obj, Dwarf_Half ndx,
            Dwarf_Small **ret_data, int *error);
} Dwarf_Obj_Access_Methods;

• get_byte_order — This function should return the endianness of the DWARF object by returning one of the constants DW_OBJECT_MSB or DW_OBJECT_LSB. Pick a side bestie, it's MSB or LSB and there's no in between.
• get_length_size — This function should return the number of bytes needed to represent a DWARF offset in the object being debugged.
• get_pointer_size — This function should return the size in bytes, in the object being debugged, of a memory address.
• get_section_count — This function should return the number of sections in the object being debugged.
• get_section_info — This function should return information about the section at the index ndx by filling in the structure of type Dwarf_Obj_Access_Section pointed to by argument ret. The Dwarf_Obj_Access_Section structure is described below, keep reading.
• load_section — This function should load the section specified by argument ndx into memory and place a pointer to the section's data into the location pointed to by argument ret_data. Get that data loaded, periodt.

Also important: the argument obj passed to these functions will be set to the pointer value in the object field of the associated Dwarf_Obj_Access_Interface structure. It's all connected, iykyk.

And the argument error is used to return an error code in case of an error. Receipts, always.

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🧚 Dwarf_Obj_Access_Section

This structure describes the layout of a section in the DWARF object. The anatomy of a section, if you will.

typedef struct {
        Dwarf_Addr addr;
        Dwarf_Unsigned size;
        const char *name;
} Dwarf_Obj_Access_Section;

• addr — A pointer to the start of the section's data. Where it all begins.
• size — The size of the section in bytes. How much room it's taking up.
• name — A pointer to a NUL-terminated string containing the name of the section. Gotta have a name, bestie.

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👑 RETURN VALUES 👑

On success, dwarf_object_init() returns DW_DLV_OK. Slay.

But in case of an error, the function returns DW_DLV_ERROR and sets the argument err. Not the vibe, but okay.

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💀 ERRORS 💀

The dwarf_object_init() function may fail with the following errors. Let's get into it:

• [DW_DLE_ARGUMENT] — One of the arguments iface or dbg was NULL. Straight up missing, couldn't even.
• [DW_DLE_DEBUG_INFO_NULL] — The underlying object did not contain debugging information. Empty. Nothing. The void.
• [DW_DLE_MEMORY] — An out of memory condition was encountered during the execution of the function. Ran out of RAM, it happens to the best of us.

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🔥 SEE ALSO 🔥

dwarf(3), dwarf_init(3), dwarf_init_elf(3), dwarf_object_finish(3) — go read these too, bestie, you'll thank me later. 🫶

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💅 Real talk: don't forget that when you're done with your Dwarf_Debug, you'll wanna call dwarf_object_finish(3) to clean up. Clean up your messes, it's a whole aesthetic.

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This iconic little page lives in the Debian-flavored DWARF world, dated back to September 29, 2011 — a whole legend. Now go debug something and make it look cute! 🌈⭐🎀