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10275 :: volatile_store codegen error ?

• mad_toothbrush (orginal) [2023-06-15T21:23:33+02:00] view original

  Hi.

  I'm exploring Nim for a bare metal project in a RISCV64 environment. I seem to be hitting a compiler codegen problem and could do with some advice.

  My setup:

  
  $ nim --version
  Nim Compiler Version 1.6.12 [Linux: amd64]
  Compiled at 2023-03-10
  Copyright (c) 2006-2023 by Andreas Rumpf
  
  git hash: 1aa9273640c0c51486cf3a7b67282fe58f360e91
  active boot switches: -d:release
  Run

  My code:

  import std/volatile
  
  when isMainModule:
    const uart_ptr = cast[ptr char](0x1000_0000)
    volatile_store(uart_ptr, 'H')
    while true:
      discard
  Run

  I build it roughly so:

  
  nim c -d:release --gc:none --cpu:riscv64 --os:standalone --passC:-Os --passC:-mcmodel=medany --passL:'-Wl,-T,linkscript.ld' --passL:-nostdlib --passL:boot.o --passL:-mcmodel=medany main.nim
  Run

  The error:

  
  nim c -d:release --gc:none --cpu:riscv64 --os:standalone --passC:-Os --passC:-mcmodel=medany --passL:'-Wl,-T,linkscript.ld' --passL:-nostdlib --passL:boot.o --passL:-mcmodel=medany main.nim
  Hint: used config file '/home/robin/.choosenim/toolchains/nim-1.6.12/config/nim.cfg' [Conf]
  Hint: used config file '/home/robin/.choosenim/toolchains/nim-1.6.12/config/config.nims' [Conf]
  Hint: used config file '/home/robin/Work/experiments/nim/nimkernel/exp/attempt.0/nim.cfg' [Conf]
  ..........................................
  CC: main.nim
  /home/robin/.cache/nim/main_r/@mmain.nim.c:24:4: error: expected identifier or '(' before 'NIM_CHAR'
     24 | *((NIM_CHAR volatile*)(((NIM_CHAR*) 268435456))) = 72;
        |    ^~~~~~~~
  /home/robin/.cache/nim/main_r/@mmain.nim.c:24:23: error: expected ')' before '(' token
     24 | *((NIM_CHAR volatile*)(((NIM_CHAR*) 268435456))) = 72;
        |                       ^
        |                       )
  Error: execution of an external compiler program '/home/robin/Work/toolchains/x-tools/riscv64-unknown-elf/bin/riscv64-unknown-elf-gcc -c  -w -fmax-errors=3 -Os -mcmodel=medany -O3 -fno-strict-aliasing -fno-ident   -I/home/robin/.choosenim/toolchains/nim-1.6.12/lib -I/home/robin/Work/experiments/nim/nimkernel/exp/attempt.0 -o /home/robin/.cache/nim/main_r/@mmain.nim.c.o /home/robin/.cache/nim/main_r/@mmain.nim.c' failed with exit code: 1
  
  
  make: *** [Makefile:5: main] Error 1
  Run

  I think this is the same issue as: https://github.com/nim-lang/Nim/issues/14623 but am not entirely sure.

  Any pointers appreciated (pun not intended!).

  Cheers

---

• Abathargh (orginal) [2023-06-15T23:34:26+02:00] view original

  Instead of putting everything at the top level, wrap it into a proc and then invoke the proc within the when isMainModule block:

  import std/volatile
  
  proc loop =
    const uart_ptr = cast[ptr char](0x1000_0000)
    volatile_store(uart_ptr, 'H')
    while true:
      discard
  
  when isMainModule:
    loop()
  Run

  It seems like it is related to that issue, but that's the only way I could make it work

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• auxym (orginal) [2023-06-15T23:41:28+02:00] view original

  Pretty sure you're correct that it's the issue you linked. Just wrap code in a main() proc or something similar as a workaround.

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• sls1005 (orginal) [2023-06-16T06:50:33+02:00] view original

  It seems that volatileStore is implemented using {.emit.}. Therefore when it's used at the top level, it emits top level C code, which is wrong, because in the C syntax, that code is not allowed at top.

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• mad_toothbrush (orginal) [2023-06-17T14:59:31+02:00] view original

  Thanks both! That fixed the problem. It would be good to have a fix. But if that's a low priority concern then perhaps a stop gap warning with relevant information to work around.

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