Re: [RFC bpf-next 4/9] bpf, x86: allow indirect jumps to r8...r15

[Anton Protopopov <a.s.protopopov@gmail.com>]

On 25/06/17 12:41PM, Alexei Starovoitov wrote:
> On Sun, Jun 15, 2025 at 1:55 AM Anton Protopopov
> <a.s.protopopov@gmail.com> wrote:
> >
> > Currently, the emit_indirect_jump() function only accepts one of the
> > RAX, RCX, ..., RBP registers as the destination. Prepare it to accept
> > R8, R9, ..., R15 as well. This is necessary to enable indirect jumps
> > support in eBPF.
> >
> > Signed-off-by: Anton Protopopov <a.s.protopopov@gmail.com>
> > ---
> >  arch/x86/net/bpf_jit_comp.c | 26 +++++++++++++++++++-------
> >  1 file changed, 19 insertions(+), 7 deletions(-)
> >
> > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> > index 923c38f212dc..37dc83d91832 100644
> > --- a/arch/x86/net/bpf_jit_comp.c
> > +++ b/arch/x86/net/bpf_jit_comp.c
> > @@ -659,7 +659,19 @@ int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
> >
> >  #define EMIT_LFENCE()  EMIT3(0x0F, 0xAE, 0xE8)
> >
> > -static void emit_indirect_jump(u8 **pprog, int reg, u8 *ip)
> > +static void __emit_indirect_jump(u8 **pprog, int reg, bool ereg)
> 
> Instead of adding bool flag make reg to be bpf reg
> instead of x86 reg, tweak the signature to
> emit_indirect_jump(..., u32 reg, ..),
> and add is_ereg(reg) inside.

Ok, will do. Didn't do it initially, because it assumes this change
(and another one similar):

-       emit_indirect_jump(&prog, 1 /* rcx */, ip + (prog - start));
+       emit_indirect_jump(&prog, BPF_REG_4 /* R4 -> rcx */, ip + (prog - start));

but with the "R4 -> rcx" actually looks ok to me.

> Also drop RFC tag next time. Let CI do the work.

Ok