Date: Fri, 7 Dec 2012 01:11:22 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: Shrikanth Kamath <shrikanth07@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: ELF symtab and ddbsymtab difference Message-ID: <20121206231122.GE3013@kib.kiev.ua> In-Reply-To: <CAEOAkMU0osWoUensNaqBH%2BPWP9bcTLZffwLVh3WeppzqKMmT0g@mail.gmail.com> References: <CAEOAkMU0osWoUensNaqBH%2BPWP9bcTLZffwLVh3WeppzqKMmT0g@mail.gmail.com>
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On Wed, Dec 05, 2012 at 12:13:24PM +0530, Shrikanth Kamath wrote:
> This is regarding the fields in the structure "elf_file_t" in link_elf.c.
> For some kernel modules the symtab field is different from the ddbsymtab
> field for some it is the same, would like to know what is the difference
> between the two and how to enable ddbsymtab?
Assuming we are talking about the link_elf.c and not about link_elf_obj.c.
The symtab and ddbsymtab are first initialized from the dynamic symbol
table in the module, and later, in the process of loading the module, if
the non-dynamic symbol table is present, ddbsymtab is rewritten to point
to the table.
>=20
> Does enabling "-g" in CFLAGS make the binary build the ddbsymtab different
> from symtab?
No. It is strip done on the module which could result in the removal of the
non-dynamic symtab.
>=20
> The problem is lookup for some symbols in the kernel module that I built
> returns with undefined, on inspecting it was getting a ENOENT from the
> function
> link_elf_lookup_symbol()
> {
> ...
> /* If we have not found it, look at the full table (if loaded) */
> if (ef->symtab =3D=3D ef->ddbsymtab)
> return (ENOENT);
> ...
> }
It is not the problem. It just means that you dynamic symbol table does
not contain the needed symbol, which is the problem. As a coincident,
you also stripped your module, making the problem to be exposed.
I guess that you should look at the EXPORT_SYMS feature of the module
Makefiles. But I also remember there were some bugs.
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