[PATCH] D140830: [AVR] correctly declare __do_copy_data and __do_clear_bss

[Ayke via Phabricator via llvm-commits]

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These two symbols are declared in object files to indicate whether .data needs to be copied from flash or .bss needs to be cleared. They are supported on avr-gcc and reduce firmware size a bit, which is especially important on very small chips.

I checked the behavior of avr-gcc and matched it as well as possible. From my investigation, it seems to work as follows:

__do_copy_data is set when the compiler finds a data symbol:

- without a section name
- with a section name starting with ".data" or ".gnu.linkonce.d"
- with a section name starting with ".rodata" or ".gnu.linkonce.r" and flash and RAM are in the same address space

__do_clear_bss is set when the compiler finds a data symbol:

- without a section name
- with a section name that starts with .bss

Simply checking whether the calculated section name starts with ".data", ".rodata" or ".bss" should result in the same behavior.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D140830

Files:
  llvm/lib/Target/AVR/AVRAsmPrinter.cpp
  llvm/lib/Target/AVR/AVRDevices.td
  llvm/lib/Target/AVR/AVRSubtarget.h
  llvm/test/CodeGen/AVR/clear-bss.ll
  llvm/test/CodeGen/AVR/no-clear-bss.ll
  llvm/test/CodeGen/AVR/no-copy-data.ll

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