On Fri, 2018-05-11 at 13:06 +0200, David Brown wrote: > For the Cortex-M devices (and probably many other RISC targets), > -fdata-sections comes at a big cost - it effectively blocks > -fsection-anchors and makes access to file-static data a lot bigger. > People often use -fdata-sections and -ffunction-sections along with > -Wl,--gc-sections with the aim of removing unused code and data (and > thus saving space, useful on small devices) - I would expect LTO > would > manage that anyway. The other purpose of these is to improve > locality > of reference - again LTO should do that for you. But even without > LTO, > I find the cost of -fdata-sections high compared to -fsection- > anchors.
Unfortunatelly having LTO doesn't make -ffunction-sections + -fdata- sections + --gc-sections useless. My test project compiled: - without LTO and without these attributes - 150824 B ROM + 4240 B RAM - with LTO and without these attributes - 133812 B ROM + 4208 B RAM - without LTO and with these attributes - 124456 B ROM + 3484 B RAM - with LTO and with these attributes - 120280 B ROM + 3680 B RAM As you see these attributes give much more than LTO in terms of size. As for the -fsection-anchors I guess this has no use for non-PIC code for arm-none-eabi. Whether I use it or not, the sizes are identical. Regards, FCh
