Known compiler warnings

[mcuee]

Use this to document some known compiler warnings which will not be fixed as of now.

[mcuee]

1. macOS

  LEX      lexer.c
/Library/Developer/CommandLineTools/usr/bin/make  all-recursive
Making all in .
  CC       avrdude-main.o
  CC       avrdude-whereami.o
  CC       avrdude-developer_opts.o
  CC       libavrdude_a-config_gram.o
  CC       libavrdude_a-lexer.o
lexer.c:2434:38: warning: comparison of integers of different signs: 'unsigned long' and 'int' [-Wsign-compare]
        if (((yy_n_chars) + number_to_move) > YY_CURRENT_BUFFER_LVALUE->yy_buf_size) {
             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 warning generated.

#1800 (comment)
From @stefanrueger

That's a known issue and we cannot do anything about it, as it's MacOS's flex that generates the code.

[mcuee]

Windows MSYS2 clang64 build:

D:/a/avrdude/avrdude/src/ser_win32.c:436:3: warning: comparison of integers of different signs: 'SOCKET' (aka 'unsigned long long') and 'const int' [-Wsign-compare]
  436 |                 FD_SET(fd->ifd, &rfds);
      |                 ^~~~~~~~~~~~~~~~~~~~~~
D:/a/_temp/msys64/clang64/include/psdk_inc/_fd_types.h:77:40: note: expanded from macro 'FD_SET'
   77 |                 if (((fd_set *)(set))->fd_array[__i] == (fd)) {         \
      |                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^   ~~
D:/a/avrdude/avrdude/src/ser_win32.c:[55](https://github.com/avrdudes/avrdude/actions/runs/8935908735/job/24545265227#step:5:56)7:3: warning: comparison of integers of different signs: 'SOCKET' (aka 'unsigned long long') and 'const int' [-Wsign-compare]
  557 |                 FD_SET(fd->ifd, &rfds);
      |                 ^~~~~~~~~~~~~~~~~~~~~~
D:/a/_temp/msys64/clang64/include/psdk_inc/_fd_types.h:77:40: note: expanded from macro 'FD_SET'
   77 |                 if (((fd_set *)(set))->fd_array[__i] == (fd)) {         \
      |                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^   ~~
2 warnings generated.

From @stefanrueger
#1541 (comment)

According to man FD_SET the function is called as it should be. I suspect Windows has a different internal representation and therefore triggers the warning. I suspect using FD_SET((unsigned long long) fd->ifd, &rfds); might silence the warning and still work, but it could be that different compilers have different macros and that you get warnings in other compilers. As far as I am concerned we could leave this as is.

[mcuee]

Take note MSYS2 mingw64 build and ucrt64 build do not generate such warnings. So it could be MSYS2 clang64 specific issue.

[mcuee]

Windows VS2019 build warnings -- not existing in VS2022 build.

  avrpart.c
C:\work\avr\avrdude_test\avrdude_main\src\avrpart.c(618,13): warning C4090: 'function': different 'const' qualifiers [C
:\work\avr\avrdude_test\avrdude_main\build_msvc\src\libavrdude.vcxproj]
  term.c
C:\work\avr\avrdude_test\avrdude_main\src\term.c(1830,3): warning C4090: 'function': different 'const' qualifiers [C:\w
ork\avr\avrdude_test\avrdude_main\build_msvc\src\libavrdude.vcxproj]
C:\work\avr\avrdude_test\avrdude_main\src\term.c(1835,3): warning C4090: 'function': different 'const' qualifiers [C:\w
ork\avr\avrdude_test\avrdude_main\build_msvc\src\libavrdude.vcxproj]
C:\work\avr\avrdude_test\avrdude_main\src\term.c(2423,7): warning C4090: 'function': different 'const' qualifiers [C:\w
ork\avr\avrdude_test\avrdude_main\build_msvc\src\libavrdude.vcxproj]
C:\work\avr\avrdude_test\avrdude_main\src\term.c(2437,5): warning C4090: 'function': different 'const' qualifiers [C:\w
ork\avr\avrdude_test\avrdude_main\build_msvc\src\libavrdude.vcxproj]
  update.c
C:\work\avr\avrdude_test\avrdude_main\src\update.c(273,24): warning C4090: 'function': different 'const' qualifiers [C:
\work\avr\avrdude_test\avrdude_main\build_msvc\src\libavrdude.vcxproj]
C:\work\avr\avrdude_test\avrdude_main\src\update.c(343,28): warning C4090: 'function': different 'const' qualifiers [C:
\work\avr\avrdude_test\avrdude_main\build_msvc\src\libavrdude.vcxproj]

[mcuee]

@stefanrueger

Just want to make sure that the warnings generated by VS2019 is harmless and no need to fix. Thanks.

[stefanrueger]

@mcuee Thanks for collecting the compiler warnings from various sources!

TLDR; In this instance the warning is given in error.

The long of it: The compiler warns about freeing a pointer that points to pointers to read-only data, something innocuous as

#include <stdlib.h>

int main() {
  const char **p = malloc(42 * sizeof *p);
  free(p);
}

It is wrong to issue a warning here, as p does point to modifiable memory as per free()'s signature. It is just that the modifiable space is meant to house pointers to r/o data. It might be that this compiler misread const char **p as char * const *p?