Dear U-Booters, First of all, I did not search the U-Boot mailing list archive with my question, because I did not see a way to do this on the U-Boot mailing list page http://lists.denx.de/mailman/listinfo/u-boot. I did search Google for "MEMORY u-boot.lds memcpy" but nothing obvious turned up. So please pardon me if this was explained before. Hopefully, you can just give me a link that explains everything.
I have been compiling and running u-boot on the Emcraft stm32f7-som board (MCU is ARM Cortex M7). Their U-boot forked off the mainline 6+ years ago, so I tried to port the latest mainline, to teach myself u-boot. The most obvious difference I can see is the relocation code, but I do not think that explains my current problem, which is that my global variable(s) were placed in on-chip flash (where text is). In the working code (again, forked off 6+ years ago), _start() explicitly copies the .data and .bss section from the flash to SRAM, and zeroes out .bss in RAM. But I have not run into such code while single-stepping through in the debugger. The readelf -S shows that the .bss in the flash, whereas it was in the RAM. Even when I looked at the stm32f429-discovery port in the mainline, I could NOT understand why the "MEMORY" part is no longer in arch/arm/cpu/u-boot.lds. In u-boot.lds, there is a suggestion to read arch/arm/lib/bss.c--which seems to be missing in the mainline. I don't know what the OVERLAY keyword is doing for the .bss, and hope that I just need to read 1 key document to understand how this is supposed to work.
Thank you very much for reading, and your understanding. w/ regards, Henry