• Masahiro Yamada's avatar
    kbuild: fix false-positive modpost warning when all symbols are trimmed · 4475dff5
    Masahiro Yamada authored
    Nathan reports that the mips defconfig emits the following warning:
    
      WARNING: modpost: Symbol info of vmlinux is missing. Unresolved symbol check will be entirely skipped.
    
    This false-positive happens when CONFIG_TRIM_UNUSED_KSYMS is enabled,
    but no CONFIG option is set to 'm'.
    
    Commit a0590473 ("nfs: fix PNFS_FLEXFILE_LAYOUT Kconfig default")
    turned the last 'm' into 'y' for the mips defconfig, and uncovered
    this issue.
    
    In this case, the module feature itself is enabled, but we have no
    module to build. As a result, CONFIG_TRIM_UNUSED_KSYMS drops all the
    instances of EXPORT_SYMBOL. Then, modpost wrongly assumes vmlinux is
    missing because vmlinux.symvers is empty. (As another false-positive
    case, you can create a module that does not use any symbol of vmlinux).
    
    The current behavior is to entirely suppress the unresolved symbol
    warnings when vmlinux is missing just because there are too many.
    I found the origin of this code in the historical git tree. [1]
    
    If this is a matter of noisiness, I think modpost can display the
    first 10 warnings, and the number of suppressed warnings at the end.
    
    You will get a bit noisier logs when you run 'make modules' without
    vmlinux, but such warnings are better to show because you never know
    the resulting modules are actually loadable or not.
    
    This commit changes the following:
    
     - If any of input *.symver files is missing, pass -w option to let
       the module build keep going with warnings instead of errors.
    
     - If there are too many (10+) unresolved symbol warnings, show only
       the first 10, and also the number of suppressed warnings.
    
    [1]: https://git.kernel.org/pub/scm/linux/kernel/git/history/history.git/commit/?id=1cc0e0529569bf6a94f6d49770aa6d4b599d2c46Reported-by: default avatarNathan Chancellor <nathan@kernel.org>
    Signed-off-by: default avatarMasahiro Yamada <masahiroy@kernel.org>
    4475dff5
Makefile.modpost 4.86 KB