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  • Masahiro Yamada's avatar
    kconfig: unify cc-option and as-option · 4d0831e8
    Masahiro Yamada authored
    cc-option and as-option are almost the same; both pass the flag to
    $(CC). The main difference is the cc-option stops before the assemble
    stage (-S option) whereas as-option stops after (-c option).
    
    I chose -S because it is slightly faster, but $(cc-option,-gz=zlib)
    returns a wrong result (https://lkml.org/lkml/2020/6/9/1529).
    It has been fixed by commit 7b169944
    
     ("Makefile: Improve compressed
    debug info support detection"), but the assembler should always be
    invoked for more reliable compiler option tests.
    
    However, you cannot simply replace -S with -c because the following
    code in lib/Kconfig.debug would break:
    
        depends on $(cc-option,-gsplit-dwarf)
    
    The combination of -c and -gsplit-dwarf does not accept /dev/null as
    output.
    
      $ cat /dev/null | gcc -gsplit-dwarf -S -x c - -o /dev/null
      $ echo $?
      0
    
      $ cat /dev/null | gcc -gsplit-dwarf -c -x c - -o /dev/null
      objcopy: Warning: '/dev/null' is not an ordinary file
      $ echo $?
      1
    
      $ cat /dev/null | gcc -gsplit-dwarf -c -x c - -o tmp.o
      $ echo $?
      0
    
    There is another flag that creates an separate file based on the
    object file path:
    
      $ cat /dev/null | gcc -ftest-coverage -c -x c - -o /dev/null
      <stdin>:1: error: cannot open /dev/null.gcno
    
    So, we cannot use /dev/null to sink the output.
    
    Align the cc-option implementation with scripts/Kbuild.include.
    
    With -c option used in cc-option, as-option is unneeded.
    
    Signed-off-by: default avatarMasahiro Yamada <masahiroy@kernel.org>
    Acked-by: default avatarWill Deacon <will@kernel.org>
    4d0831e8