xref: /freebsd/contrib/elftoolchain/libdwarf/dwarf_loclist.3 (revision ae500c1ff8974130f7f2692772cf288b90349e0d)

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.\" $Id: dwarf_loclist.3 3644 2018-10-15 19:55:01Z jkoshy $
.\"
.Dd November 9, 2011
.Dt DWARF_LOCLIST 3
.Os
.Sh NAME
.Nm dwarf_loclist ,
.Nm dwarf_loclist_n
.Nd retrieve DWARF location expression information
.Sh LIBRARY
.Lb libdwarf
.Sh SYNOPSIS
.In libdwarf.h
.Ft int
.Fo dwarf_loclist
.Fa "Dwarf_Attribute at"
.Fa "Dwarf_Locdesc **llbuf"
.Fa "Dwarf_Signed *listlen"
.Fa "Dwarf_Error *error"
.Fc
.Ft int
.Fo dwarf_loclist_n
.Fa "Dwarf_Attribute at"
.Fa "Dwarf_Locdesc ***llbuf"
.Fa "Dwarf_Signed *listlen"
.Fa "Dwarf_Error *error"
.Fc
.Sh DESCRIPTION
These functions retrieve the location expressions
associated with a DWARF attribute.
.Pp
Note: function
.Fn dwarf_loclist
is deprecated.
New application code should instead use function
.Fn dwarf_loclist_n
.Pp
Function
.Fn dwarf_loclist_n
retrieves the list of location expressions associated with a DWARF
attribute.
Argument
.Ar at
should reference a valid DWARF attribute.
Argument
.Ar llbuf
should point to a location which will hold a returned array of
pointers to
.Vt Dwarf_Locdesc
descriptors.
Argument
.Ar listlen
should point to a location which will be set to the number of
elements contained in the returned array.
If argument
.Ar err
is not NULL, it will be used to store error information in case
of an error.
.Pp
Function
.Fn dwarf_loclist
retrieves the first location expression associated with an attribute.
Argument
.Ar at
should reference a valid DWARF attribute.
Argument
.Ar llbuf
should point to a location which will hold the returned pointer
to a
.Vt Dwarf_Locdesc
descriptor.
Argument
.Ar listlen
should point to a location which will be always set to 1.
If argument
.Ar err
is not NULL, it will be used to store error information in case
of an error.
.Pp
.Vt Dwarf_Locdesc
descriptors are defined in the header file
.In libdwarf.h ,
and consist of following fields:
.Pp
.Bl -tag -width ".Va ld_cents" -compact
.It Va ld_lopc
The lowest program counter address covered by the descriptor.
This field will be set to 0 if the descriptor is not associated with
an address range.
.It Va ld_hipc
The highest program counter address covered by the descriptor.
This field will be set to 0 if the descriptor is not associated with
an address range.
.It Va ld_cents
The number of entries returned in
.Va ld_s
field.
.It Va ld_s
Pointer to an array of
.Vt Dwarf_Loc
descriptors.
.El
.Pp
Each
.Vt Dwarf_Loc
descriptor represents one operation of a location expression.
These descriptors are defined in the header file
.In libdwarf.h ,
and consist of following fields:
.Pp
.Bl -tag -width ".Va lr_number2" -compact
.It Va lr_atom
The operator name, one of the
.Dv DW_OP_*
constants defined in the header file
.In dwarf.h .
.It Va lr_number
The first operand of this operation.
.It Va lr_number2
The second operand of this operation.
.It Va lr_offset
The byte offset of this operation within the containing location
expression.
.El
.Ss Memory Management
The memory area used for the descriptor array returned in argument
.Ar llbuf
is allocated by the
.Lb libdwarf .
When the descriptor array is no longer needed, application code should
use function
.Xr dwarf_dealloc 3
to free the memory area in the following manner:
.Bl -enum
.It
First, the
.Ar ld_s
field of each
.Vt Dwarf_Locdesc
descriptor should be deallocated using the allocation type
.Dv DW_DLA_LOC_BLOCK .
.It
Then, the application should free each
.Vt Dwarf_Locdesc
descriptor using the allocation type
.Dv DW_DLA_LOCDESC .
.It
Finally, the
.Va llbuf
pointer should be deallocated using the allocation type
.Dv DW_DLA_LIST .
.El
.Sh RETURN VALUES
On success, these functions returns
.Dv DW_DLV_OK .
In case of an error, they return
.Dv DW_DLV_ERROR
and set the argument
.Ar err .
.Sh EXAMPLES
To retrieve the location list associated with an attribute, use:
.Bd -literal -offset indent
Dwarf_Attribute at;
Dwarf_Locdesc **llbuf;
Dwarf_Signed lcnt;
Dwarf_Loc *lr;
Dwarf_Error de;
int i;

if (dwarf_loclist_n(at, &llbuf, &lcnt, &de) != DW_DLV_OK)
	errx(EXIT_FAILURE, "dwarf_loclist_n failed: %s",
	    dwarf_errmsg(de));

for (i = 0; i < lcnt; i++) {
	/* ... Use llbuf[i] ... */
	for (j = 0; (Dwarf_Half) j < llbuf[i]->ld_cents; j++) {
		lr = &llbuf[i]->ld_s[j];
		/* ... Use each Dwarf_Loc descriptor ... */
	}
	dwarf_dealloc(dbg, llbuf[i]->ld_s, DW_DLA_LOC_BLOCK);
	dwarf_dealloc(dbg, llbuf[i], DW_DLA_LOCDESC);
}
dwarf_dealloc(dbg, llbuf, DW_DLA_LIST);
.Ed
.Sh ERRORS
These functions can fail with:
.Bl -tag -width ".Bq Er DW_DLE_ARGUMENT"
.It Bq Er DW_DLE_ARGUMENT
One of the arguments
.Ar at ,
.Ar llbuf
or
.Ar listlen
was NULL.
.It Bq Er DW_DLE_ARGUMENT
The attribute provided by argument
.Ar at
does not contain a location expression or is not associated with a
location expression list.
.El
.Sh SEE ALSO
.Xr dwarf 3 ,
.Xr dwarf_dealloc 3 ,
.Xr dwarf_get_loclist_entry 3 ,
.Xr dwarf_loclist_from_expr 3 ,
.Xr dwarf_loclist_from_expr_a 3