LEN_CHECK was being fed a hardcoded '1' which was being treated as an int. This led GCC 10.2.1 to emit a warning about comparison between signed/unsigned integers because the builder->max member is unsigned: ell/dhcp-util.c: In function ‘_dhcp_message_builder_append’: ell/dhcp-util.c:55:49: error: comparison of integer expressions of different signedness: ‘int’ and ‘unsigned int’ [-Werror=sign-compare] 55 | if ((builder)->pos - (builder)->start + (next) > (builder)->max) \ | ^ ell/dhcp-util.c:65:3: note: in expansion of macro ‘LEN_CHECK’ 65 | LEN_CHECK(builder, 1); | ^~~~~~~~~ cc1: all warnings being treated as errors To fix this explicitly use '1U' so the compiler treats it as unsigned. --- ell/dhcp-util.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/ell/dhcp-util.c b/ell/dhcp-util.c index 7809e52..af09856 100644 --- a/ell/dhcp-util.c +++ b/ell/dhcp-util.c @@ -62,7 +62,7 @@ bool _dhcp_message_builder_append(struct dhcp_message_builder *builder, switch (code) { case DHCP_OPTION_PAD: case DHCP_OPTION_END: - LEN_CHECK(builder, 1); + LEN_CHECK(builder, 1U); builder->pos[0] = code; builder->pos += 1; -- 2.26.2