.\" Copyright (c) 2011 Kai Wang
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.\" $Id: dwarf_add_expr_gen.3 3640 2018-10-14 14:09:13Z jkoshy $
.\"
.Dd September 9, 2011
.Dt DWARF_ADD_EXPR_GEN 3
.Os
.Sh NAME
.Nm dwarf_add_expr_gen
.Nd add an operator to a location expression descriptor
.Sh LIBRARY
.Lb libdwarf
.Sh SYNOPSIS
.In libdwarf.h
.Ft "Dwarf_Unsigned"
.Fo dwarf_add_expr_gen
.Fa "Dwarf_P_Expr expr"
.Fa "Dwarf_Small opcode"
.Fa "Dwarf_Unsigned val1"
.Fa "Dwarf_Unsigned val2"
.Fa "Dwarf_Error *err"
.Fc
.Sh DESCRIPTION
Function
.Fn dwarf_add_expr_gen
adds a location expression operator to the location expression
descriptor referenced by argument
.Ar expr .
.Pp
Argument
.Ar expr
should reference a location expression descriptor allocated using
the function
.Xr dwarf_new_expr 3 .
.Pp
Argument
.Ar opcode
specifies the operation code of the location expression operator.
Valid values for this argument are those denoted by the
.Dv DW_OP_ Ns *
constants defined in
.In libdwarf.h .
.Pp
To generate a
.Dv DW_OP_addr
operation, application code should instead use
.Xr dwarf_add_expr_addr_b 3 .
.Pp
Argument
.Ar val1
specifies the first operand of the location expression operator.
.Pp
Argument
.Ar val2
specifies the second operand of the location expression operator.
.Pp
If argument
.Ar err
is not NULL, it will be used to store error information in case
of an error.
.Sh RETURN VALUES
On success, function
.Fn dwarf_add_expr_gen
returns the size in bytes of the location expression byte stream
generated.
In case of an error, function
.Fn dwarf_add_expr_gen
returns
.Dv DW_DLV_NOCOUNT
and sets the argument
.Ar err .
.Sh ERRORS
Function
.Fn dwarf_add_expr_gen
can fail with:
.Bl -tag -width ".Bq Er DW_DLE_LOC_EXPR_BAD"
.It Bq Er DW_DLE_ARGUMENT
Argument
.Ar expr
was NULL.
.It Bq Er DW_DLE_LOC_EXPR_BAD
The operation code specified in argument
.Ar opcode
was invalid.
.It Bq Er DW_DLE_MEMORY
An out of memory condition was encountered during the execution of
the function.
.El
.Sh SEE ALSO
.Xr dwarf 3 ,
.Xr dwarf_add_AT_location_expr 3 ,
.Xr dwarf_add_expr_addr 3 ,
.Xr dwarf_add_expr_addr_b 3 ,
.Xr dwarf_expr_current_offset 3 ,
.Xr dwarf_expr_into_block 3 ,
.Xr dwarf_new_expr 3