Re: modload(8) v.s. alias

[Paul Goyette <paul%whooppee.com@localhost>]

Our in-kernel linker does not understand weak references.  It would
be a lot of work to implement, and there are some issues that would
need to be considered carefully.

For example, if module A defines a weak alias, and module B is loaded
and resolves the alias, what do you do if module C gets loaded and we
discover a "strong" definition of the same symbol?  Do you keep the
original resolution, or do you re-resolve it to the new definition?


On Mon, 9 Mar 2020, Rin Okuyama wrote:

> Hi,
>
> modload(8) fails if some depended functions are alias, at least
> on m68k. For example:
>
>   # uname -a
>   NetBSD  9.99.49 NetBSD 9.99.49 (GENERIC) #6: Mon Mar  9 22:53:07 JST 2020 
> rin@latipes:/build/src/sys/arch/sun2/compile/GENERIC sun2
>   # modload nfs
>   [xxx.xxx] kobj_checksyms, 998: [nfs]: linker error: symbol '__ffssi2' not 
> found
>   [xxx.xxx] WARNING: module error: unable to affix module 'nfs', error 8
>   modload: nfs: Exec format error
>   #
>
> Here, __ffssi4 is weak alias of ffs on m68k:
>
>   # nm /netbsd | grep __ffssi2
>   0012327c W __ffssi2
>   # nm /netbsd | grep 0012327c
>   0012327c W __ffssi2
>   0012327c T ffs
>   #
>
> If this symbol is turned into a ``real'' object by attached patch,
> modload(8) and loaded module work fine:
>
>   # nm /netbsd | grep __ffssi4
>   0012327c T __ffssi2
>   # modload nfs
>   # mount_nfs server:/path /mnt
>   # ls /mnt
>   foo bar baz ...
>   #
>
> Is this a bug or feature? How can I fix this problem?
>
> Thanks,
> rin
> ----
> Index: common/lib/libc/arch/m68k/string/ffs.S
> ===================================================================
> RCS file: /cvsroot/src/common/lib/libc/arch/m68k/string/ffs.S,v
> retrieving revision 1.7
> diff -p -u -r1.7 ffs.S
> --- common/lib/libc/arch/m68k/string/ffs.S	9 Mar 2020 13:36:10 -0000 
> 1.7
> +++ common/lib/libc/arch/m68k/string/ffs.S	9 Mar 2020 14:09:13 -0000
> @@ -45,7 +45,11 @@
> /* bit = ffs(value) */
> +#ifdef _LIBC
> WEAK_ALIAS(__ffssi2,ffs)
> +#else /* KERNEL */
> +#define ffs __ffssi2
> +#endif
> #if (!defined(__mc68010__) && !defined(__mcoldfire__)) || 
> defined(__mcfisac__)
>
> !DSPAM:5e664fb8246343444541299!

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