Re: [PATCH 1/4] glibc: Perform rseq(2) registration at C startup and thread creation (v7)

[Carlos O'Donell]

On 4/5/19 5:16 AM, Florian Weimer wrote:
> * Carlos O'Donell:
> > It is valuable that it be a trap, particularly for constant pools because
> > it means that a jump into the constant pool will trap.
>
> Sorry, I don't understand why this matters in this context.  Would you
> please elaborate?

Sorry, I wasn't very clear.

My point is only that any accidental jumps, either with off-by-one (like you
fixed in gcc/glibc's signal unwinding most recently), result in a process fault
rather than executing RSEQ_SIG as a valid instruction *and then* continuing
onwards to the handler.

A process fault is achieved either by a trap, or an invalid instruction, or
a privileged insn (like suggested for MIPS in this thread).

--
Cheers,
Carlos.