Re: [PATCH] RISC-V: Handle R_RISCV_32 in modules

[Palmer Dabbelt]

On Mon, 11 Jun 2018 00:54:00 PDT (-0700), schwab@xxxxxxx wrote:
> On Jun 08 2018, Palmer Dabbelt <palmer@xxxxxxxxxx> wrote:
>
> > On Thu, 07 Jun 2018 03:27:27 PDT (-0700), schwab@xxxxxxx wrote:
> > > With CONFIG_MODVERSIONS=y the R_RISCV_32 relocation is used by the
> > > __kcrctab section.
> > >
> > > Signed-off-by: Andreas Schwab <schwab@xxxxxxx>
> > > ---
> > >  arch/riscv/kernel/module.c | 12 ++++++++++++
> > >  1 file changed, 12 insertions(+)
> > >
> > > diff --git a/arch/riscv/kernel/module.c b/arch/riscv/kernel/module.c
> > > index 5dddba301d..1d5e9b934b 100644
> > > --- a/arch/riscv/kernel/module.c
> > > +++ b/arch/riscv/kernel/module.c
> > > @@ -17,6 +17,17 @@
> > >  #include <linux/errno.h>
> > >  #include <linux/moduleloader.h>
> > >
> > > +static int apply_r_riscv_32_rela(struct module *me, u32 *location, Elf_Addr v)
> > > +{
> > > +	if (v != (u32)v) {
> >
> > My worry with this kind of check is that it relies on some sort of
> > undefined behavior in C and that at some point in the future GCC will just
> > go decide the check can never fail.  I checked and GCC doesn't elide these
> > checks now, so I might be wrong.
> >
> > Is this defined to do what it looks like it's doing?
>
> This is unsigned arithmetic, thus fully defined.

Great, thanks!  I guess I'm just a bit paranoid :)