Makefile: Enable linker garbage collection

This patch enables -ffunction-sections, -fdata-sections and
-Wl,--gc-sections for host builds. These flags already get passed by
firmware builds anyway, so having host builds match that behavior should
be a good idea in general. They may also occasionally help save a bit of
code size (though not much since vboot is a library, but I still get
about half a KB out of futility), and they will prevent clang from
omitting relocations for function calls inside the same file, which
means we don't have to splatter test_mockable all over our codebase
anymore. (We still need it for vb2_get_gbb() since that is so small that
both GCC and clang want to inline it, even if they are outputting a
discrete copy anyway.)

(Also add a comment about why GenerateGuid() has nothing do to with this
even though it is also a weak function, and why it is like that.)

BRANCH=None
BUG=chromium:991812
TEST=make runtests with both GCC and clang

Change-Id: Iede9d29e20b99b75a0c86bc7ecb907d2a0e5e3a1
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1754969
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>

1 files changed, 9 insertions, 1 deletions

diff --git a/cgpt/cgpt_common.c b/cgpt/cgpt_common.c
index db180bef..e98a4533 100644
--- a/cgpt/cgpt_common.c
+++ b/cgpt/cgpt_common.c
@@ -1086,7 +1086,15 @@ void PMBRToStr(struct pmbr *pmbr, char *str, unsigned int buflen) {
   }
 }
 
-/* Optional */
+/*
+ * This is here because some CGPT functionality is provided in libvboot_host.a
+ * for other host utilities. GenerateGuid() is implemented (in cgpt.c which is
+ * *not* linked into libvboot_host.a) by calling into libuuid. We don't want to
+ * mandate libuuid as a dependency for every utilitity that wants to link
+ * libvboot_host.a, since they usually don't use the functionality that needs
+ * to generate new UUIDs anyway (just other functionality implemented in the
+ * same files).
+ */
 #ifndef HAVE_MACOS
 __attribute__((weak)) int GenerateGuid(Guid *newguid) { return CGPT_FAILED; };
 #endif