Commits on Jul 3, 2024

1. Compile with -funsigned-char …

   Due to 'char' (unless explicitly set) being signed or unsigned depending
   on architecture, e.g on x86 it's signed, while on Arm it's unsigned,
   this can lead to subtle bugs such if you use a plain char as a byte
   thinking it's unsigned on all platforms (maybe you live in the world of
   Arm).
   
   What we can do is tell the compiler to treat 'char' as unsigned by
   default, thus it will be consistent across platforms. Seeing as most of
   the time it doesn't matter whether char is signed or unsigned, it
   really only matters when you're dealing with 'bytes', which means it
   makes sense to default char to unsigned.
   
   The Linux Kernel made this change at the end of 2022.
   
   This will also allow in the future to convert our u_char's to char's
   (which will now be unsigned) and pass them directly into the libc
   functions for example, without the need for casting.
   
   Here is what the ISO C standard has to say
   
   From §6.2.5 Types ¶15
   
     The three types char, signed char, and unsigned char are collectively
     called the character types. The implementation shall define char to
     have the same range, representation, and behavior as either signed
     char or unsigned char.[45]
   
   and from Footnote 45)
   
     CHAR_MIN, defined in <limits.h>, will have one of the values 0 or
     SCHAR_MIN, and this can be used to distinguish the two options.
     Irrespective of the choice made, char is a separate type from the
     other two and is not compatible with either.
   
   If you're still unsure why you'd want this change...
   
   It was never clear to me, why we used u_char, perhaps that was used as
   an alternative to -funsigned-char...
   
   But that still leaves the potential for bugs with char being unsigned vs
   signed...
   
   Then because we use u_char but often need to pass such things into libc
   (and perhaps other functions) which normally take a 'char' we need to
   cast these cases.
   
   So this change brings at least two (or more) benefits
   
     1) Removal of potential for char unsigned vs signed bugs.
   
     2) Removal of a bunch of casts. Reducing casting to the bare minimum
        is good. This helps the compiler to do proper type checking.
   
     3) Readability/maintainability, everything is now just char...
   
   What if you want to work with bytes?
   
   Well with char being unsigned (everywhere) you can of course use char.
   
   However it would be much better to use the uint8_t type for that to
   clearly signify that intention.
   
   Link: <https://lore.kernel.org/lkml/[email protected]/>
   Link: <https://lore.kernel.org/lkml/[email protected]/>
   Link: <https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3bc753c06dd02a3517c9b498e3846ebfc94ac3ee>
   Link: <https://www.iso-9899.info/n1570.html#6.2.5p15>
   Suggested-by: Alejandro Colomar <[email protected]>
   Reviewed-by: Alejandro Colomar <[email protected]>
   Signed-off-by: Andrew Clayton <[email protected]>

   

   ac000 committed Jul 3, 2024
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