On Thu, Jul 30, 2009 at 11:49:23AM -0700, David VomLehn wrote:
> To: GCC Help Mailing List <email@example.com>,
> Linux MIPS Mailing List <firstname.lastname@example.org>
> Subject: Relocation problem with MIPS kernel modules
> Content-Type: text/plain; charset=us-ascii
> I have a MIPS loadable kernel module that, when I try to insmod it, causes the
> kernel to emit the message:
> module xyz: dangerous relocation
> This message appears in three different places in arch/mips/kernel/module.c,
> but this one is coming from apply_r_mips_lo16_rel(). The module code at
I'll change the messages to indicate the relocation type.
> the location at which the error message is generated appears to be pretty
> lw v0,28564(s1)
> with the expected relocation type of R_MIPS_LO16. The relocation before it
> is R_MIPS_HI16, as expected, but for a different symbol. Before *that*
> is another R_MIPS_HI16 relocation entry for yet a third symbol.
> According to the MIPS ABI, for what it's worth, "Each relocation type of
> R_MIPS_HI16 must have an associated R_MIPS_LO16 entry immediately following
> it in the list of relocations." So, what's actually getting generated by
> gcc and linker differs from the closest thing we have to an ABI of record for
> MIPS processors.
The GNU tools as an extension over the MIPS ABI allows an arbitrary number of
R_MIPS_HI16 relocations to be followed by a R_MIPS_LO16 symbol. All
relocations of this sequence must use the same symbol, of course. This is
a very old extension; I think it predates the Linux/MIPS port.