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FreeBSD 11.0 - man page for dwarf_new_expr (freebsd section 3)

DWARF_NEW_EXPR(3)					   BSD Library Functions Manual 					 DWARF_NEW_EXPR(3)

dwarf_new_expr -- create a location expression descriptor
DWARF Access Library (libdwarf, -ldwarf)
#include <libdwarf.h> Dwarf_P_Expr dwarf_new_expr(Dwarf_P_Debug dbg, Dwarf_Error *err);
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.
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.
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.
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; }
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 BSD