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Put each functions in a separate section by using -ffunction-sections, then discard the non-referenced ones in the linker with -gc-sections. Force keeping a few special symbols by using the KEEP() linker directive. This modification is not saving a lot of spaces per se, but will enable larger code pruning with future optional features. Signed-off-by: Vincent Palatin <vpalatin@chromium.org> BRANCH=none BUG=none TEST=make buildall, manually check discarded symbols in the .map file and run on Spring and Link. The size delta is the following: Link: total 85.7k -> 84.9k (.text 60.3k -> 59.5k) Spring: total 59.2k -> 57.2k (.text 44.4k -> 42.5k) Change-Id: Ib6eb0d3f2cc4fc172c9fc26acac2e486921690a3 Reviewed-on: https://chromium-review.googlesource.com/189224 Reviewed-by: Randall Spangler <rspangler@chromium.org> Commit-Queue: Vincent Palatin <vpalatin@chromium.org> Tested-by: Vincent Palatin <vpalatin@chromium.org>
In the most general case, the flash layout looks something like this: +---------------------+ | Reserved for EC use | +---------------------+ +---------------------+ | Vblock B | +---------------------+ | RW firmware B | +---------------------+ +---------------------+ | Vblock A | +---------------------+ | RW firmware A | +---------------------+ +---------------------+ | FMAP | +---------------------+ | Public root key | +---------------------+ | Read-only firmware | +---------------------+ BIOS firmware (and kernel) put the vblock info at the start of each image where it's easy to find. The Blizzard EC expects the firmware vector table to come first, so we have to put the vblock at the end. This means we have to know where to look for it, but that's built into the FMAP and the RO firmware anyway, so that's not an issue. The RO firmware doesn't need a vblock of course, but it does need some reserved space for vboot-related things. Using SHA256/RSA4096, the vblock is 2468 bytes (0x9a4), while the public root key is 1064 bytes (0x428) and the current FMAP is 644 bytes (0x284). If we reserve 4K at the top of each FW image, that should give us plenty of room for vboot-related stuff.