DWARF_INIT(3) | Library Functions Manual | DWARF_INIT(3)

# NAME

`dwarf_init`, `dwarf_elf_init` — allocate a DWARF debug descriptor

# LIBRARY

DWARF Access Library (libdwarf, -ldwarf)

# SYNOPSIS

`#include <libdwarf.h>`

int
`dwarf_init`(int fd, int mode, Dwarf_Handler errhand, Dwarf_Ptr errarg, Dwarf_Debug *ret, Dwarf_Error *err);

int
`dwarf_elf_init`(Elf *elf, int mode, Dwarf_Handler errhand, Dwarf_Ptr errarg, Dwarf_Debug *ret, Dwarf_Error *err);

# DESCRIPTION

These functions allocate and return a Dwarf_Debug instance for the object denoted by argument fd or elf. This instance would be used for subsequent access to debugging information in the object by other functions in the DWARF(3) library.

For function `dwarf_init`(), argument fd denotes an open file descriptor referencing a compilation object. Function `dwarf_init`() implicitly allocates an Elf descriptor for argument fd.

For function `dwarf_elf_init`(), argument elf denotes a descriptor returned by elf_begin(3) or elf_memory(3).

Argument mode specifies the access mode desired. It should be at least as permissive as the mode with which the file descriptor fd or the ELF descriptor elf was created with. Legal values for argument mode are:

DW_DLC_RDWR
  Permit reading and writing of DWARF information.
DW_DLC_READ
  Operate in read-only mode.
DW_DLC_WRITE
  Permit writing of DWARF information.

Argument errhand denotes a function to be called in case of an error. If this argument is `NULL` then a default error handling scheme is used. See dwarf(3) for a description of the error handling scheme used by the DWARF(3) library.

Argument errarg is passed to the error handler function denoted by argument errhand when it is invoked.

Argument ret points to the memory location that will hold a Dwarf_Debug reference on a successful call these functions.

Argument err references a memory location that would hold a Dwarf_Error descriptor in case of an error.

## Memory Management

The Dwarf_Debug instance returned by these functions should be freed using `dwarf_finish`().

# IMPLEMENTATION NOTES

The current implementation does not support access modes `DW_DLC_RDWR` and `DW_DLC_WRITE`.

# RETURN VALUES

These functions return the following values:

[`DW_DLV_OK`]
  This return value indicates a successful return.
[`DW_DLV_ERROR`]
  The operation failed.
[`DW_DLV_NO_ENTRY`]
  The object specified by arguments fd or elf did not contain debug information.

# EXAMPLES

To initialize a Dwarf_Debug instance from a open file descriptor referencing an ELF object, and with the default error handler, use:

    Dwarf_Error err;
    Dwarf_Debug dbg;

    if (dwarf_init(fd, DW_DLC_READ, NULL, NULL, &dbg, &err) !=
        DW_DLV_OK)
    	errx(EXIT_FAILURE, "dwarf_init: %s", dwarf_errmsg(err));

# SEE ALSO

dwarf(3), dwarf_errmsg(3), dwarf_finish(3), dwarf_get_elf(3), elf_begin(3), elf_memory(3)

March 13, 2022 | NetBSD 11.0