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Message-ID: <aWSL3DlSf5WA20lf@linux.ibm.com>
Date: Mon, 12 Jan 2026 11:21:24 +0530
From: Saket Kumar Bhaskar <skb99@...ux.ibm.com>
To: adubey@...ux.ibm.com
Cc: bpf@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
hbathini@...ux.ibm.com, sachinpb@...ux.ibm.com, venkat88@...ux.ibm.com,
andrii@...nel.org, eddyz87@...il.com, mykolal@...com, ast@...nel.org,
daniel@...earbox.net, martin.lau@...ux.dev, song@...nel.org,
yonghong.song@...ux.dev, john.fastabend@...il.com, kpsingh@...nel.org,
sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org,
christophe.leroy@...roup.eu, naveen@...nel.org, maddy@...ux.ibm.com,
mpe@...erman.id.au, npiggin@...il.com, memxor@...il.com,
iii@...ux.ibm.com, shuah@...nel.org
Subject: Re: [PATCH 5/6] powerpc64/bpf: Support exceptions
On Mon, Jan 05, 2026 at 04:22:11PM +0530, adubey@...ux.ibm.com wrote:
> From: Abhishek Dubey <adubey@...ux.ibm.com>
>
> The modified prologue/epilogue generation code now
> enables exception-callback to use the stack frame of
> the program marked as exception boundary, where callee
> saved registers are stored.
>
> As per ppc64 ABIv2 documentation[1], r14-r31 are callee
> saved registers. BPF programs on ppc64 already saves
> r26-r31 registers. Saving the remaining set of callee
> saved registers(r14-r25) is handled in the next patch.
>
> [1] https://ftp.rtems.org/pub/rtems/people/sebh/ABI64BitOpenPOWERv1.1_16July2015_pub.pdf
>
> Following is exceptions selftest result on ppc64le:
>
> # ./test_progs -t exceptions
> #100/1 exceptions/exception_throw_always_1:OK
> #100/2 exceptions/exception_throw_always_2:OK
> #100/3 exceptions/exception_throw_unwind_1:OK
> #100/4 exceptions/exception_throw_unwind_2:OK
> #100/5 exceptions/exception_throw_default:OK
> #100/6 exceptions/exception_throw_default_value:OK
> #100/7 exceptions/exception_tail_call:OK
> #100/8 exceptions/exception_ext:OK
> #100/9 exceptions/exception_ext_mod_cb_runtime:OK
> #100/10 exceptions/exception_throw_subprog:OK
> #100/11 exceptions/exception_assert_nz_gfunc:OK
> #100/12 exceptions/exception_assert_zero_gfunc:OK
> #100/13 exceptions/exception_assert_neg_gfunc:OK
> #100/14 exceptions/exception_assert_pos_gfunc:OK
> #100/15 exceptions/exception_assert_negeq_gfunc:OK
> #100/16 exceptions/exception_assert_poseq_gfunc:OK
> #100/17 exceptions/exception_assert_nz_gfunc_with:OK
> #100/18 exceptions/exception_assert_zero_gfunc_with:OK
> #100/19 exceptions/exception_assert_neg_gfunc_with:OK
> #100/20 exceptions/exception_assert_pos_gfunc_with:OK
> #100/21 exceptions/exception_assert_negeq_gfunc_with:OK
> #100/22 exceptions/exception_assert_poseq_gfunc_with:OK
> #100/23 exceptions/exception_bad_assert_nz_gfunc:OK
> #100/24 exceptions/exception_bad_assert_zero_gfunc:OK
> #100/25 exceptions/exception_bad_assert_neg_gfunc:OK
> #100/26 exceptions/exception_bad_assert_pos_gfunc:OK
> #100/27 exceptions/exception_bad_assert_negeq_gfunc:OK
> #100/28 exceptions/exception_bad_assert_poseq_gfunc:OK
> #100/29 exceptions/exception_bad_assert_nz_gfunc_with:OK
> #100/30 exceptions/exception_bad_assert_zero_gfunc_with:OK
> #100/31 exceptions/exception_bad_assert_neg_gfunc_with:OK
> #100/32 exceptions/exception_bad_assert_pos_gfunc_with:OK
> #100/33 exceptions/exception_bad_assert_negeq_gfunc_with:OK
> #100/34 exceptions/exception_bad_assert_poseq_gfunc_with:OK
> #100/35 exceptions/exception_assert_range:OK
> #100/36 exceptions/exception_assert_range_with:OK
> #100/37 exceptions/exception_bad_assert_range:OK
> #100/38 exceptions/exception_bad_assert_range_with:OK
> #100/39 exceptions/non-throwing fentry -> exception_cb:OK
> #100/40 exceptions/throwing fentry -> exception_cb:OK
> #100/41 exceptions/non-throwing fexit -> exception_cb:OK
> #100/42 exceptions/throwing fexit -> exception_cb:OK
> #100/43 exceptions/throwing extension (with custom cb) -> exception_cb:OK
> #100/44 exceptions/throwing extension -> global func in exception_cb:OK
> #100/45 exceptions/exception_ext_mod_cb_runtime:OK
> #100/46 exceptions/throwing extension (with custom cb) -> global func in exception_cb:OK
> #100/47 exceptions/exception_ext:OK
> #100/48 exceptions/non-throwing fentry -> non-throwing subprog:OK
> #100/49 exceptions/throwing fentry -> non-throwing subprog:OK
> #100/50 exceptions/non-throwing fentry -> throwing subprog:OK
> #100/51 exceptions/throwing fentry -> throwing subprog:OK
> #100/52 exceptions/non-throwing fexit -> non-throwing subprog:OK
> #100/53 exceptions/throwing fexit -> non-throwing subprog:OK
> #100/54 exceptions/non-throwing fexit -> throwing subprog:OK
> #100/55 exceptions/throwing fexit -> throwing subprog:OK
> #100/56 exceptions/non-throwing fmod_ret -> non-throwing subprog:OK
> #100/57 exceptions/non-throwing fmod_ret -> non-throwing global subprog:OK
> #100/58 exceptions/non-throwing extension -> non-throwing subprog:OK
> #100/59 exceptions/non-throwing extension -> throwing subprog:OK
> #100/60 exceptions/non-throwing extension -> non-throwing subprog:OK
> #100/61 exceptions/non-throwing extension -> throwing global subprog:OK
> #100/62 exceptions/throwing extension -> throwing global subprog:OK
> #100/63 exceptions/throwing extension -> non-throwing global subprog:OK
> #100/64 exceptions/non-throwing extension -> main subprog:OK
> #100/65 exceptions/throwing extension -> main subprog:OK
> #100/66 exceptions/reject_exception_cb_type_1:OK
> #100/67 exceptions/reject_exception_cb_type_2:OK
> #100/68 exceptions/reject_exception_cb_type_3:OK
> #100/69 exceptions/reject_exception_cb_type_4:OK
> #100/70 exceptions/reject_async_callback_throw:OK
> #100/71 exceptions/reject_with_lock:OK
> #100/72 exceptions/reject_subprog_with_lock:OK
> #100/73 exceptions/reject_with_rcu_read_lock:OK
> #100/74 exceptions/reject_subprog_with_rcu_read_lock:OK
> #100/75 exceptions/reject_with_rbtree_add_throw:OK
> #100/76 exceptions/reject_with_reference:OK
> #100/77 exceptions/reject_with_cb_reference:OK
> #100/78 exceptions/reject_with_cb:OK
> #100/79 exceptions/reject_with_subprog_reference:OK
> #100/80 exceptions/reject_throwing_exception_cb:OK
> #100/81 exceptions/reject_exception_cb_call_global_func:OK
> #100/82 exceptions/reject_exception_cb_call_static_func:OK
> #100/83 exceptions/reject_multiple_exception_cb:OK
> #100/84 exceptions/reject_exception_throw_cb:OK
> #100/85 exceptions/reject_exception_throw_cb_diff:OK
> #100/86 exceptions/reject_set_exception_cb_bad_ret1:OK
> #100/87 exceptions/reject_set_exception_cb_bad_ret2:OK
> #100/88 exceptions/check_assert_eq_int_min:OK
> #100/89 exceptions/check_assert_eq_int_max:OK
> #100/90 exceptions/check_assert_eq_zero:OK
> #100/91 exceptions/check_assert_eq_llong_min:OK
> #100/92 exceptions/check_assert_eq_llong_max:OK
> #100/93 exceptions/check_assert_lt_pos:OK
> #100/94 exceptions/check_assert_lt_zero:OK
> #100/95 exceptions/check_assert_lt_neg:OK
> #100/96 exceptions/check_assert_le_pos:OK
> #100/97 exceptions/check_assert_le_zero:OK
> #100/98 exceptions/check_assert_le_neg:OK
> #100/99 exceptions/check_assert_gt_pos:OK
> #100/100 exceptions/check_assert_gt_zero:OK
> #100/101 exceptions/check_assert_gt_neg:OK
> #100/102 exceptions/check_assert_ge_pos:OK
> #100/103 exceptions/check_assert_ge_zero:OK
> #100/104 exceptions/check_assert_ge_neg:OK
> #100/105 exceptions/check_assert_range_s64:OK
> #100/106 exceptions/check_assert_range_u64:OK
> #100/107 exceptions/check_assert_single_range_s64:OK
> #100/108 exceptions/check_assert_single_range_u64:OK
> #100/109 exceptions/check_assert_generic:OK
> #100/110 exceptions/check_assert_with_return:OK
> #100 exceptions:OK
> Summary: 1/110 PASSED, 0 SKIPPED, 0 FAILED
>
It would be great to include this selftest output in the cover letter
instead, since it makes the git log excessively long.
Thanks,
Saket
> Signed-off-by: Abhishek Dubey <adubey@...ux.ibm.com>
> ---
> arch/powerpc/net/bpf_jit.h | 2 ++
> arch/powerpc/net/bpf_jit_comp.c | 7 ++++
> arch/powerpc/net/bpf_jit_comp64.c | 53 +++++++++++++++++++++----------
> 3 files changed, 45 insertions(+), 17 deletions(-)
>
> diff --git a/arch/powerpc/net/bpf_jit.h b/arch/powerpc/net/bpf_jit.h
> index 98e8b1f9c2f9..b9316780a501 100644
> --- a/arch/powerpc/net/bpf_jit.h
> +++ b/arch/powerpc/net/bpf_jit.h
> @@ -177,6 +177,8 @@ struct codegen_context {
> u64 arena_vm_start;
> u64 user_vm_start;
> bool is_subprog;
> + bool exception_boundary;
> + bool exception_cb;
> };
>
> #define bpf_to_ppc(r) (ctx->b2p[r])
> diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
> index b09d294084d4..3c030a7d8e73 100644
> --- a/arch/powerpc/net/bpf_jit_comp.c
> +++ b/arch/powerpc/net/bpf_jit_comp.c
> @@ -207,6 +207,8 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
> cgctx.arena_vm_start = bpf_arena_get_kern_vm_start(fp->aux->arena);
> cgctx.user_vm_start = bpf_arena_get_user_vm_start(fp->aux->arena);
> cgctx.is_subprog = bpf_is_subprog(fp);
> + cgctx.exception_boundary = fp->aux->exception_boundary;
> + cgctx.exception_cb = fp->aux->exception_cb;
>
> /* Scouting faux-generate pass 0 */
> if (bpf_jit_build_body(fp, NULL, NULL, &cgctx, addrs, 0, false)) {
> @@ -436,6 +438,11 @@ void bpf_jit_free(struct bpf_prog *fp)
> bpf_prog_unlock_free(fp);
> }
>
> +bool bpf_jit_supports_exceptions(void)
> +{
> + return IS_ENABLED(CONFIG_PPC64);
> +}
> +
> bool bpf_jit_supports_subprog_tailcalls(void)
> {
> return IS_ENABLED(CONFIG_PPC64);
> diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
> index 0f3af67914d6..5ec8e3654098 100644
> --- a/arch/powerpc/net/bpf_jit_comp64.c
> +++ b/arch/powerpc/net/bpf_jit_comp64.c
> @@ -85,7 +85,9 @@ static inline bool bpf_has_stack_frame(struct codegen_context *ctx)
> * - the bpf program uses its stack area
> * The latter condition is deduced from the usage of BPF_REG_FP
> */
> - return ctx->seen & SEEN_FUNC || bpf_is_seen_register(ctx, bpf_to_ppc(BPF_REG_FP));
> + return ctx->seen & SEEN_FUNC ||
> + bpf_is_seen_register(ctx, bpf_to_ppc(BPF_REG_FP)) ||
> + ctx->exception_cb;
> }
>
> /*
> @@ -180,23 +182,32 @@ void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx)
> EMIT(PPC_RAW_STDU(_R1, _R1, -(BPF_PPC_STACKFRAME + ctx->stack_size)));
> }
>
> - /*
> - * Back up non-volatile regs -- BPF registers 6-10
> - * If we haven't created our own stack frame, we save these
> - * in the protected zone below the previous stack frame
> - */
> - for (i = BPF_REG_6; i <= BPF_REG_10; i++)
> - if (bpf_is_seen_register(ctx, bpf_to_ppc(i)))
> - EMIT(PPC_RAW_STD(bpf_to_ppc(i), _R1, bpf_jit_stack_offsetof(ctx, bpf_to_ppc(i))));
> + if (!ctx->exception_cb) {
> + /*
> + * Back up non-volatile regs -- BPF registers 6-10
> + * If we haven't created our own stack frame, we save these
> + * in the protected zone below the previous stack frame
> + */
> + for (i = BPF_REG_6; i <= BPF_REG_10; i++)
> + if (ctx->exception_boundary || bpf_is_seen_register(ctx, bpf_to_ppc(i)))
> + EMIT(PPC_RAW_STD(bpf_to_ppc(i), _R1,
> + bpf_jit_stack_offsetof(ctx, bpf_to_ppc(i))));
>
> - if (ctx->arena_vm_start)
> - EMIT(PPC_RAW_STD(bpf_to_ppc(ARENA_VM_START), _R1,
> + if (ctx->exception_boundary || ctx->arena_vm_start)
> + EMIT(PPC_RAW_STD(bpf_to_ppc(ARENA_VM_START), _R1,
> bpf_jit_stack_offsetof(ctx, bpf_to_ppc(ARENA_VM_START))));
>
> - /* Setup frame pointer to point to the bpf stack area */
> - if (bpf_is_seen_register(ctx, bpf_to_ppc(BPF_REG_FP)))
> - EMIT(PPC_RAW_ADDI(bpf_to_ppc(BPF_REG_FP), _R1,
> + /* Setup frame pointer to point to the bpf stack area */
> + if (bpf_is_seen_register(ctx, bpf_to_ppc(BPF_REG_FP)))
> + EMIT(PPC_RAW_ADDI(bpf_to_ppc(BPF_REG_FP), _R1,
> STACK_FRAME_MIN_SIZE + ctx->stack_size));
> + } else {
> + /*
> + * Exception callback receives Frame Pointer of main
> + * program as third arg
> + */
> + EMIT(PPC_RAW_MR(_R1, _R5));
> + }
>
> if (ctx->arena_vm_start)
> PPC_LI64(bpf_to_ppc(ARENA_VM_START), ctx->arena_vm_start);
> @@ -208,17 +219,25 @@ static void bpf_jit_emit_common_epilogue(u32 *image, struct codegen_context *ctx
>
> /* Restore NVRs */
> for (i = BPF_REG_6; i <= BPF_REG_10; i++)
> - if (bpf_is_seen_register(ctx, bpf_to_ppc(i)))
> + if (ctx->exception_cb || bpf_is_seen_register(ctx, bpf_to_ppc(i)))
> EMIT(PPC_RAW_LD(bpf_to_ppc(i), _R1, bpf_jit_stack_offsetof(ctx, bpf_to_ppc(i))));
>
> - if (ctx->arena_vm_start)
> + if (ctx->exception_cb || ctx->arena_vm_start)
> EMIT(PPC_RAW_LD(bpf_to_ppc(ARENA_VM_START), _R1,
> bpf_jit_stack_offsetof(ctx, bpf_to_ppc(ARENA_VM_START))));
>
> + if (ctx->exception_cb) {
> + /*
> + * LR value from boundary-frame is received as second parameter
> + * in exception callback.
> + */
> + EMIT(PPC_RAW_MTLR(_R4));
> + }
> +
> /* Tear down our stack frame */
> if (bpf_has_stack_frame(ctx)) {
> EMIT(PPC_RAW_ADDI(_R1, _R1, BPF_PPC_STACKFRAME + ctx->stack_size));
> - if (ctx->seen & SEEN_FUNC) {
> + if (ctx->seen & SEEN_FUNC || ctx->exception_cb) {
> EMIT(PPC_RAW_LD(_R0, _R1, PPC_LR_STKOFF));
> EMIT(PPC_RAW_MTLR(_R0));
> }
> --
> 2.48.1
>
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