DWARF_NEW_EXPR(3) | Library Functions Manual | DWARF_NEW_EXPR(3)

# NAME

`dwarf_new_expr` —
create a location expression descriptor

# LIBRARY

DWARF Access Library (libdwarf, -ldwarf)

# SYNOPSIS

`#include <libdwarf.h>`

Dwarf_P_Expr
`dwarf_new_expr`(Dwarf_P_Debug dbg, Dwarf_Error *err);

# DESCRIPTION

Function `dwarf_new_expr`() allocates a DWARF location expression descriptor used to build up a location expression stream.

The application can use the functions dwarf_add_expr_gen(3) and dwarf_add_expr_addr_b(3) to add location expression operators to the created descriptor. When done, the application can call the function dwarf_expr_into_block(3) to retrieve the generated byte stream for the location expression, or call the function dwarf_add_AT_location_expr(3) to create an attribute with the location expression stream as its value.

Argument dbg should reference a DWARF producer instance allocated using dwarf_producer_init(3) or dwarf_producer_init_b(3).

If argument err is not NULL, it will be used to store error information in case of an error.

# RETURN VALUES

On success, function `dwarf_new_expr`() returns the created location expression descriptor. In case of an error, function `dwarf_new_expr`() returns `DW_DLV_BADADDR` and sets the argument err.

# ERRORS

Function `dwarf_new_expr`() can fail with:

[`DW_DLE_ARGUMENT`]
  Argument dbg was NULL.
[`DW_DLE_MEMORY`]
  An out of memory condition was encountered during the execution of the function.

# EXAMPLES

To create a location expression descriptor, add location expression operators to it and to retrieve the generated byte stream, use:

    Dwarf_P_Debug dbg;
    Dwarf_Error de;
    Dwarf_P_Expr pe;
    Dwarf_Addr buf;
    Dwarf_Unsigned len;

    /* ...Assume that `dbg' refers to a DWARF producer instance... */

    if ((pe = dwarf_new_expr(dbg, &de)) == DW_DLV_BADADDR) {
    	warnx("dwarf_new_expr failed: %s", dwarf_errmsg(-1));
    	return;
    }

    if (dwarf_add_expr_gen(pe, DW_OP_regx, 55, 0, &de) ==
        DW_DLV_NOCOUNT) {
    	warnx("dwarf_add_expr_gen failed: %s", dwarf_errmsg(-1));
    	return;
    }

    if ((buf = dwarf_expr_into_block(pe, &len, &de)) ==
        DW_DLV_BADADDR) {
    	warnx("dwarf_expr_into_block failed: %s",
    	    dwarf_errmsg(-1));
    	return;
    }

# SEE ALSO

dwarf(3), dwarf_add_AT_location_expr(3), dwarf_add_expr_gen(3), dwarf_add_expr_addr(3), dwarf_add_expr_addr_b(3), dwarf_expr_current_offset(3), dwarf_expr_into_block(3), dwarf_producer_init(3), dwarf_producer_init_b(3)

September 8, 2011 | NetBSD 9.4