DWARF_NEXT_CU_HEADER(3) | Library Functions Manual | DWARF_NEXT_CU_HEADER(3)

# NAME

`dwarf_next_cu_header`, `dwarf_next_cu_header_b`, `dwarf_next_cu_header_c` —
step through compilation units in a DWARF debug context

# LIBRARY

DWARF Access Library (libdwarf, -ldwarf)

# SYNOPSIS

`#include <libdwarf.h>`

int
`dwarf_next_cu_header`(Dwarf_Debug dbg, Dwarf_Unsigned *cu_length, Dwarf_Half *cu_version, Dwarf_Off *cu_abbrev_offset, Dwarf_Half *cu_pointer_size, Dwarf_Unsigned *cu_next_offset, Dwarf_Error *err);

int
`dwarf_next_cu_header_b`(Dwarf_Debug dbg, Dwarf_Unsigned *cu_length, Dwarf_Half *cu_version, Dwarf_Off *cu_abbrev_offset, Dwarf_Half *cu_pointer_size, Dwarf_Half *cu_offset_size, Dwarf_Half *cu_extension_size, Dwarf_Unsigned *cu_next_offset, Dwarf_Error *err);

int
`dwarf_next_cu_header_c`(Dwarf_Debug dbg, Dwarf_Bool is_info, Dwarf_Unsigned *cu_length, Dwarf_Half *cu_version, Dwarf_Off *cu_abbrev_offset, Dwarf_Half *cu_pointer_size, Dwarf_Half *cu_offset_size, Dwarf_Half *cu_extension_size, Dwarf_Sig8 *type_signature, Dwarf_Unsigned *type_offset, Dwarf_Unsigned *cu_next_offset, Dwarf_Error *err);

# DESCRIPTION

These functions are used to step through compilation or type units associated with a DWARF debug context, optionally returning information about the unit.

Function `dwarf_next_cu_header_c`() is the API recommended for new application code. Function `dwarf_next_cu_header`() and `dwarf_next_cu_header_b`() can only operate on compilation units associated with the “.debug_info” section. They are less general than function `dwarf_next_cu_header_c`(), and are deprecated for use by new application code.

Argument dbg should reference a DWARF debug context allocated using dwarf_init(3). If argument is_info is set to 1, the function returns information for compilation units found in the “.debug_info” section. If argument is_info is set to 0, the function returns information for type units found in the “.debug_types” sections. Argument cu_length should point to a location that will be set to the length of the compilation or type unit. Argument cu_version should point to a location that will be set to the version number for the compilation or type unit. Argument cu_abbrev_offset should point to a location that will be set to the starting offset (in the “.debug_abbrev” section) of the set of debugging information entry abbreviations associated with this compilation or type unit. Argument cu_pointer_size should point to a location that will be set to the size in bytes of an address for the machine architecture of the underlying object being debugged. Argument cu_offset_size should point to a location that will be set to the size in bytes for a DWARF offset in the compilation or type unit. Argument cu_extension_size is only needed for processing MIPS/IRIX objects that use a non-standard DWARF format. It should point to a location that will be set to 4 for normal objects and to 0 for non-standard ones. Argument type_signature and type_offset is only needed for processing type units. Argument type_signature should point to a location that will be set to the 64-bit unique signature of the type described in the type unit. Argument type_offset should point to a location that will be set to the offset of the debugging information entry that describes the type. Argument cu_next_offset should point to a location that will be set to the offset of the next compilation unit header in the “.debug_info” section, or the offset of the next type unit header in the “.debug_types” section. Argument err should point to a location that will hold an error descriptor in case of an error.

Function `dwarf_next_cu_header_b`() is identical to function `dwarf_next_cu_header_c`() except that it does not provide arguments is_info, type_signature and type_offset.

Function `dwarf_next_cu_header`() is identical to function `dwarf_next_cu_header_b`() except that it does not provide arguments cu_offset_size and cu_extension_size.

A value of NULL may be used for any of the arguments cu_length, cu_version, cu_abbrev_offset, cu_pointer_size, cu_offset_size, cu_extension_size, type_signature, type_offset, cu_next_offset and err if the caller is not interested in the respective value.

## Iterating Through Compilation Units in a Debug Context

The first call to function `dwarf_next_cu_header_c`() for a given debug context with argument is_info set to 1 will return information about the first compilation unit in the “.debug_info” section. Subsequent calls to the function will iterate through the remaining compilation units in the section. On stepping past the last compilation unit in the section, function `dwarf_next_cu_header_c`() returns `DW_DLV_NO_ENTRY` and resets its internal state. The next call to the function will restart from the first compilation unit in the section.

## Iterating Through Type Units in a Debug Context

When a DWARF debug context is allocated using dwarf_init(3), an internal pointer associated with the context will point to the first “.debug_types” section found in the debug object. The first call to function `dwarf_next_cu_header_c`() for the debug context with argument is_info set to 0 will return information about the first type unit in that “.debug_types” section. Subsequent calls to the function will iterate through the remaining type units in the section. On stepping past the last type unit in the debug context, function `dwarf_next_cu_header_c`() returns `DW_DLV_NO_ENTRY` and resets its internal state. The next call to the function will restart from the first type unit in the “.debug_types” section.

If the debug object contains multiple “.debug_types” sections, the function `dwarf_next_types_section`() can be called to move the internal pointer to the next “.debug_types” section. As a result, subsequent calls of the function `dwarf_next_cu_header_c`() will operate on the new “.debug_types” section. Function `dwarf_next_types_section`() returns `DW_DLV_NO_ENTRY` when there are no more “.debug_types” sections left in the debug object.

# RETURN VALUES

On success, these functions return `DW_DLV_OK`. In case of an error, they return `DW_DLV_ERROR` and set argument err. When there are no more compilation units left to traverse, they return `DW_DLV_NO_ENTRY`.

# ERRORS

These functions can fail with the following error:

[`DW_DLE_ARGUMENT`]
  Argument dbg was NULL.

# SEE ALSO

dwarf(3), dwarf_get_cu_die_offset_given_cu_header_offset(3), dwarf_init(3), dwarf_next_types_section(3), dwarf_siblingof(3)

December 21, 2014 | NetBSD 9.3