> -----Original Message----- > From: Stephen Hemminger <[email protected]> > Sent: Sunday 21 June 2026 17:24 > To: [email protected] > Cc: Christophe Fontaine <[email protected]>; [email protected]; Stephen > Hemminger > <[email protected]>; Wathsala Vithanage > <[email protected]>; Konstantin Ananyev > <[email protected]>; Marat Khalili <[email protected]>; > Jerin Jacob > <[email protected]> > Subject: [PATCH v3 3/6] bpf/arm64: fix offset type to allow a negative jump > > From: Christophe Fontaine <[email protected]> > > The DPDK BPF JIT standalone test test_ld_mbuf1 fails on arm64. > It does: > r6 = r1 // mbuf > r0 = *(u8 *)pkt[0] // BPF_ABS > if ((r0 & 0xf0) == 0x40) > goto parse > r0 = 0 > exit // epilogue E0 > parse: > r0 = *(u8 *)pkt[r0 + 3] // BPF_IND > ... > exit > > emit_return_zero_if_src_zero() returns 0 by branching to a function > epilogue. The target maybe a previous epilogue so branch > might be backwards; therefore the offset needs to be negative. > > The offset was stored in a uint16_t, so a negative value wrapped to a > large positive number; emit_b() then branched past the end of the > program and faulted at run time. > > Fixes: 111e2a747a4f ("bpf/arm: add basic arithmetic operations") > Cc: [email protected] > > Signed-off-by: Christophe Fontaine <[email protected]> > Signed-off-by: Stephen Hemminger <[email protected]> > --- > lib/bpf/bpf_jit_arm64.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/lib/bpf/bpf_jit_arm64.c b/lib/bpf/bpf_jit_arm64.c > index a04ef33a9c..67e42015de 100644 > --- a/lib/bpf/bpf_jit_arm64.c > +++ b/lib/bpf/bpf_jit_arm64.c > @@ -957,10 +957,12 @@ static void > emit_return_zero_if_src_zero(struct a64_jit_ctx *ctx, bool is64, uint8_t src) > { > uint8_t r0 = ebpf_to_a64_reg(ctx, EBPF_REG_0); > - uint16_t jump_to_epilogue; > + int32_t jump_to_epilogue; > > emit_cbnz(ctx, is64, src, 3); > emit_mov_imm(ctx, is64, r0, 0); > + > + /* maybe backwards branch to earlier epilogue */ > jump_to_epilogue = (ctx->program_start + ctx->program_sz) - ctx->idx; > emit_b(ctx, jump_to_epilogue); > } > -- > 2.53.0
I still wish it was not called program_sz here, but the fix is not wrong, so Acked-by: Marat Khalili <[email protected]>
