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.\" Id: dwarf_next_cu_header.3 4013 2023-10-14 22:40:50Z kaiwang27
.\"
.Dd October 15, 2023
.Dt DWARF_NEXT_CU_HEADER 3
.Os
.Sh NAME
.Nm dwarf_next_cu_header ,
.Nm dwarf_next_cu_header_b ,
.Nm dwarf_next_cu_header_c ,
.Nm dwarf_next_cu_header_d
.Nd step through compilation units in a DWARF debug context
.Sh LIBRARY
.Lb libdwarf
.Sh SYNOPSIS
.In libdwarf.h
.Ft int
.Fo dwarf_next_cu_header
.Fa "Dwarf_Debug dbg"
.Fa "Dwarf_Unsigned *cu_length"
.Fa "Dwarf_Half *cu_version"
.Fa "Dwarf_Off *cu_abbrev_offset"
.Fa "Dwarf_Half *cu_pointer_size"
.Fa "Dwarf_Unsigned *cu_next_offset"
.Fa "Dwarf_Error *err"
.Fc
.Ft int
.Fo dwarf_next_cu_header_b
.Fa "Dwarf_Debug dbg"
.Fa "Dwarf_Unsigned *cu_length"
.Fa "Dwarf_Half *cu_version"
.Fa "Dwarf_Off *cu_abbrev_offset"
.Fa "Dwarf_Half *cu_pointer_size"
.Fa "Dwarf_Half *cu_offset_size"
.Fa "Dwarf_Half *cu_extension_size"
.Fa "Dwarf_Unsigned *cu_next_offset"
.Fa "Dwarf_Error *err"
.Fc
.Ft int
.Fo dwarf_next_cu_header_c
.Fa "Dwarf_Debug dbg"
.Fa "Dwarf_Bool is_info"
.Fa "Dwarf_Unsigned *cu_length"
.Fa "Dwarf_Half *cu_version"
.Fa "Dwarf_Off *cu_abbrev_offset"
.Fa "Dwarf_Half *cu_pointer_size"
.Fa "Dwarf_Half *cu_offset_size"
.Fa "Dwarf_Half *cu_extension_size"
.Fa "Dwarf_Sig8 *type_signature"
.Fa "Dwarf_Unsigned *type_offset"
.Fa "Dwarf_Unsigned *cu_next_offset"
.Fa "Dwarf_Error *err"
.Fc
.Ft int
.Fo dwarf_next_cu_header_d
.Fa "Dwarf_Debug dbg"
.Fa "Dwarf_Bool is_info"
.Fa "Dwarf_Unsigned *cu_length"
.Fa "Dwarf_Half *cu_version"
.Fa "Dwarf_Off *cu_abbrev_offset"
.Fa "Dwarf_Half *cu_pointer_size"
.Fa "Dwarf_Half *cu_offset_size"
.Fa "Dwarf_Half *cu_extension_size"
.Fa "Dwarf_Sig8 *type_signature"
.Fa "Dwarf_Unsigned *type_offset"
.Fa "Dwarf_Unsigned *cu_next_offset"
.Fa "Dwarf_Half *cu_type"
.Fa "Dwarf_Error *err"
.Fc
.Sh DESCRIPTION
These functions are used to step through compilation or type units
associated with a DWARF debug context, optionally returning information
about the unit.
.Pp
Function
.Fn dwarf_next_cu_header_d
is the API recommended for new application code.
Function
.Fn dwarf_next_cu_header_c
can not return the unit type defined by the DWARF5 standard.
Function
.Fn dwarf_next_cu_header
and
.Fn dwarf_next_cu_header_b
can only operate on compilation units associated with the
.Dq \&.debug_info
section.
The earlier revisions are less general than function
.Fn dwarf_next_cu_header_d ,
and are deprecated for use by new application code.
.Pp
Argument
.Fa dbg
should reference a DWARF debug context allocated using
.Xr dwarf_init 3 .
If argument
.Fa is_info
is set to 1,
the function returns information for compilation units found in the
.Dq \&.debug_info
section.
If argument
.Fa is_info
is set to 0,
the function returns information for type units found in the
.Dq \&.debug_types
sections.
Argument
.Fa cu_length
should point to a location that will be set to the
length of the compilation or type unit.
Argument
.Fa cu_version
should point to a location that will be set to the
version number for the compilation or type unit.
Argument
.Fa cu_abbrev_offset
should point to a location that will be set to the
starting offset (in the
.Dq .debug_abbrev
section) of the set of debugging information entry abbreviations
associated with this compilation or type unit.
Argument
.Fa 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
.Fa 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
.Fa 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
.Fa type_signature
and
.Fa type_offset
is only needed for processing type units.
Argument
.Fa 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
.Fa type_offset
should point to a location that will be set to the offset of the debugging
information entry that describes the type.
Argument
.Fa cu_next_offset
should point to a location that will be set to the
offset of the next compilation unit header in the
.Dq \&.debug_info
section,
or the offset of the next type unit header in the
.Dq \&.debug_types
section.
Argument
.Fa cu_type
should point to a location that will be set to the
type of the compilation unit.
Argument
.Fa err
should point to a location that will hold an error descriptor in case
of an error.
.Pp
Function
.Fn dwarf_next_cu_header_c
is identical to function
.Fn dwarf_next_cu_header_d
except that it does not provide argument
.Fa cu_type .
.Pp
Function
.Fn dwarf_next_cu_header_b
is identical to function
.Fn dwarf_next_cu_header_c
except that it does not provide arguments
.Fa is_info ,
.Fa type_signature
and
.Fa type_offset .
.Pp
Function
.Fn dwarf_next_cu_header
is identical to function
.Fn dwarf_next_cu_header_b
except that it does not provide arguments
.Fa cu_offset_size
and
.Fa cu_extension_size .
.Pp
A value of
.Dv NULL
may be used for any of the arguments
.Fa cu_length ,
.Fa cu_version ,
.Fa cu_abbrev_offset ,
.Fa cu_pointer_size ,
.Fa cu_offset_size ,
.Fa cu_extension_size ,
.Fa type_signature ,
.Fa type_offset ,
.Fa cu_next_offset ,
.Fa cu_type
and
.Fa err
if the caller is not interested in the respective value.
.Ss Iterating Through Compilation Units in a Debug Context
The first call to function
.Fn dwarf_next_cu_header_c
for a given debug context with argument
.Fa is_info
set to 1 will return information about the first
compilation unit in the
.Dq \&.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
.Fn dwarf_next_cu_header_d
returns
.Dv 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.
.Ss Iterating Through Type Units in a Debug Context
When a DWARF debug context is allocated using
.Xr dwarf_init 3 ,
an internal pointer associated with the context will point to the first
.Dq \&.debug_types
section found in the debug object.
The first call to function
.Fn dwarf_next_cu_header_d
for the debug context with argument
.Fa is_info
set to 0 will return information about the first
type unit in that
.Dq \&.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
.Fn dwarf_next_cu_header_d
returns
.Dv DW_DLV_NO_ENTRY
and resets its internal state.
The next call to the function will restart from the first type
unit in the
.Dq \&.debug_types
section.
.Pp
If the debug object contains multiple
.Dq \&.debug_types
sections, the function
.Fn dwarf_next_types_section
can be called to move the internal pointer to the next
.Dq \&.debug_types
section.
As a result, subsequent calls of the function
.Fn dwarf_next_cu_header_d
will operate on the new
.Dq \&.debug_types
section.
Function
.Fn dwarf_next_types_section
returns
.Dv DW_DLV_NO_ENTRY
when there are no more
.Dq \&.debug_types
sections left in the debug object.
.Sh RETURN VALUES
On success, these functions return
.Dv DW_DLV_OK .
In case of an error, they return
.Dv DW_DLV_ERROR
and set argument
.Fa err .
When there are no more compilation units left to traverse, they return
.Dv DW_DLV_NO_ENTRY .
.Sh ERRORS
These functions can fail with the following error:
.Bl -tag -width ".Bq Er DW_DLE_ARGUMENT"
.It Bq Er DW_DLE_ARGUMENT
Argument
.Va dbg
was
.Dv NULL .
.El
.Sh SEE ALSO
.Xr dwarf 3 ,
.Xr dwarf_get_cu_die_offset_given_cu_header_offset 3 ,
.Xr dwarf_init 3 ,
.Xr dwarf_next_types_section 3 ,
.Xr dwarf_siblingof 3