This is the mail archive of the mailing list for the binutils project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: [PATCH] bfd: xtensa: ignore overflow in hight part of const16 relocation

On Fri, Dec 7, 2018 at 1:31 PM
<> wrote:
> On Fri, Dec 7, 2018 at 1:17 PM Max Filippov <> wrote:
> >
> > 32-bit constants loaded by two const16 opcodes that involve relocation
> > (e.g. calculated as a sum of a symbol and a constant) may overflow,
> > resulting in linking error with the following message:
> >
> >   dangerous relocation: const16: cannot encode: (_start+0x70000000)
> >
> > They whould wrap around instead.
> >
> > bfd/
> > 2018-12-07  Max Filippov  <>
> >
> >         * elf32-xtensa.c (elf_xtensa_do_reloc): Only use bits 16..31 of
> >         the relocated value for the high part const16 immediate.
> This is generally OK. I would probably change the comment to, "Ignore
> high sixteen bits". The way it is worded now it sounds like a 32-bit
> overflow, so more than ~4GB.

It is a 32-bit overflow of the relocated value, and when the value is
shifted right by 16 to extract immediate field for the const16 it doesn't
fit into that 16-bit field.
So the fix is to ignore all bits above the bit 31 of the relocated value,
i.e. to only use bits 16..31 for the const16 immediate.

-- Max

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]