[otbn] Make embeddable OTBN ELF objects back into ET_REL files
Signed-off-by: Rupert Swarbrick <rswarbrick@lowrisc.org>
diff --git a/util/otbn_build.py b/util/otbn_build.py
index 51256c8..f95a5a4 100755
--- a/util/otbn_build.py
+++ b/util/otbn_build.py
@@ -193,6 +193,17 @@
out_embedded_obj])
call_rv32_objcopy(args)
+
+ # After objcopy has finished, we have to do a little surgery to
+ # overwrite the ELF e_type field (a 16-bit little-endian number at file
+ # offset 0x10). It will currently be 0x2 (ET_EXEC), which means a
+ # fully-linked executable file. Binutils doesn't want to link with
+ # anything of type ET_EXEC (since it usually wouldn't make any sense to
+ # do so). Hack the type to be 0x1 (ET_REL), which means an object file.
+ with open(out_embedded_obj, 'r+b') as emb_file:
+ emb_file.seek(0x10)
+ emb_file.write(b'\1\0')
+
except subprocess.CalledProcessError as e:
# Show a nicer error message if any of the called programs fail.
log.fatal("Command {!r} returned non-zero exit code {}".format(
