diff mbox series

[bpf-next,v1,2/3] bpf: Zero index arg error string for dynptr and iter

Message ID 20241127230147.4158201-3-memxor@gmail.com (mailing list archive)
State New
Delegated to: BPF
Headers show
Series Fix missing process_iter_arg type check | expand

Checks

Context Check Description
bpf/vmtest-bpf-next-PR success PR summary
bpf/vmtest-bpf-next-VM_Test-0 success Logs for Lint
bpf/vmtest-bpf-next-VM_Test-4 success Logs for aarch64-gcc / build / build for aarch64 with gcc
bpf/vmtest-bpf-next-VM_Test-2 success Logs for Unittests
bpf/vmtest-bpf-next-VM_Test-3 success Logs for Validate matrix.py
bpf/vmtest-bpf-next-VM_Test-1 success Logs for ShellCheck
bpf/vmtest-bpf-next-VM_Test-5 success Logs for aarch64-gcc / build-release
bpf/vmtest-bpf-next-VM_Test-10 success Logs for aarch64-gcc / veristat
bpf/vmtest-bpf-next-VM_Test-11 success Logs for s390x-gcc / build / build for s390x with gcc
bpf/vmtest-bpf-next-VM_Test-12 success Logs for s390x-gcc / build-release
bpf/vmtest-bpf-next-VM_Test-33 success Logs for x86_64-llvm-17 / veristat
bpf/vmtest-bpf-next-VM_Test-35 success Logs for x86_64-llvm-18 / build-release / build for x86_64 with llvm-18-O2
bpf/vmtest-bpf-next-VM_Test-34 success Logs for x86_64-llvm-18 / build / build for x86_64 with llvm-18
bpf/vmtest-bpf-next-VM_Test-41 success Logs for x86_64-llvm-18 / veristat
bpf/vmtest-bpf-next-VM_Test-16 success Logs for s390x-gcc / veristat
bpf/vmtest-bpf-next-VM_Test-19 success Logs for x86_64-gcc / build-release
bpf/vmtest-bpf-next-VM_Test-27 success Logs for x86_64-llvm-17 / build / build for x86_64 with llvm-17
bpf/vmtest-bpf-next-VM_Test-17 success Logs for set-matrix
bpf/vmtest-bpf-next-VM_Test-28 success Logs for x86_64-llvm-17 / build-release / build for x86_64 with llvm-17-O2
bpf/vmtest-bpf-next-VM_Test-18 success Logs for x86_64-gcc / build / build for x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-6 success Logs for aarch64-gcc / test (test_maps, false, 360) / test_maps on aarch64 with gcc
bpf/vmtest-bpf-next-VM_Test-9 success Logs for aarch64-gcc / test (test_verifier, false, 360) / test_verifier on aarch64 with gcc
bpf/vmtest-bpf-next-VM_Test-32 success Logs for x86_64-llvm-17 / test (test_verifier, false, 360) / test_verifier on x86_64 with llvm-17
bpf/vmtest-bpf-next-VM_Test-37 success Logs for x86_64-llvm-18 / test (test_progs, false, 360) / test_progs on x86_64 with llvm-18
bpf/vmtest-bpf-next-VM_Test-36 success Logs for x86_64-llvm-18 / test (test_maps, false, 360) / test_maps on x86_64 with llvm-18
bpf/vmtest-bpf-next-VM_Test-40 success Logs for x86_64-llvm-18 / test (test_verifier, false, 360) / test_verifier on x86_64 with llvm-18
bpf/vmtest-bpf-next-VM_Test-38 success Logs for x86_64-llvm-18 / test (test_progs_cpuv4, false, 360) / test_progs_cpuv4 on x86_64 with llvm-18
bpf/vmtest-bpf-next-VM_Test-21 success Logs for x86_64-gcc / test (test_progs, false, 360) / test_progs on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-29 success Logs for x86_64-llvm-17 / test (test_maps, false, 360) / test_maps on x86_64 with llvm-17
bpf/vmtest-bpf-next-VM_Test-30 success Logs for x86_64-llvm-17 / test (test_progs, false, 360) / test_progs on x86_64 with llvm-17
bpf/vmtest-bpf-next-VM_Test-20 success Logs for x86_64-gcc / test (test_maps, false, 360) / test_maps on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-26 success Logs for x86_64-gcc / veristat / veristat on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-25 success Logs for x86_64-gcc / test (test_verifier, false, 360) / test_verifier on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-23 success Logs for x86_64-gcc / test (test_progs_no_alu32_parallel, true, 30) / test_progs_no_alu32_parallel on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-24 success Logs for x86_64-gcc / test (test_progs_parallel, true, 30) / test_progs_parallel on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-15 success Logs for s390x-gcc / test (test_verifier, false, 360) / test_verifier on s390x with gcc
bpf/vmtest-bpf-next-VM_Test-22 success Logs for x86_64-gcc / test (test_progs_no_alu32, false, 360) / test_progs_no_alu32 on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-31 success Logs for x86_64-llvm-17 / test (test_progs_no_alu32, false, 360) / test_progs_no_alu32 on x86_64 with llvm-17
bpf/vmtest-bpf-next-VM_Test-7 success Logs for aarch64-gcc / test (test_progs, false, 360) / test_progs on aarch64 with gcc
bpf/vmtest-bpf-next-VM_Test-8 success Logs for aarch64-gcc / test (test_progs_no_alu32, false, 360) / test_progs_no_alu32 on aarch64 with gcc
bpf/vmtest-bpf-next-VM_Test-39 success Logs for x86_64-llvm-18 / test (test_progs_no_alu32, false, 360) / test_progs_no_alu32 on x86_64 with llvm-18
bpf/vmtest-bpf-next-VM_Test-13 success Logs for s390x-gcc / test (test_progs, false, 360) / test_progs on s390x with gcc
bpf/vmtest-bpf-next-VM_Test-14 success Logs for s390x-gcc / test (test_progs_no_alu32, false, 360) / test_progs_no_alu32 on s390x with gcc
netdev/series_format success Posting correctly formatted
netdev/tree_selection success Clearly marked for bpf-next
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 3 this patch: 3
netdev/build_tools success Errors and warnings before: 0 (+0) this patch: 0 (+0)
netdev/cc_maintainers warning 19 maintainers not CCed: alexandre.torgue@foss.st.com shuah@kernel.org song@kernel.org john.fastabend@gmail.com houtao1@huawei.com martin.lau@linux.dev linux-kselftest@vger.kernel.org mykolal@fb.com kpsingh@kernel.org cupertino.miranda@oracle.com jolsa@kernel.org haoluo@google.com linux-arm-kernel@lists.infradead.org mattbobrowski@google.com mcoquelin.stm32@gmail.com laoar.shao@gmail.com yonghong.song@linux.dev linux-stm32@st-md-mailman.stormreply.com sdf@fomichev.me
netdev/build_clang success Errors and warnings before: 3 this patch: 3
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 14 this patch: 14
netdev/checkpatch warning WARNING: line length of 84 exceeds 80 columns WARNING: line length of 90 exceeds 80 columns
netdev/build_clang_rust success No Rust files in patch. Skipping build
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0

Commit Message

Kumar Kartikeya Dwivedi Nov. 27, 2024, 11:01 p.m. UTC 
Andrii spotted that process_dynptr_func's rejection of incorrect
argument register type will print an error string where argument numbers
are not zero-indexed, unlike elsewhere in the verifier.  Fix this by
subtracting 1 from regno. The same scenario exists for iterator
messages. Fix selftest error strings that match on the exact argument
number while we're at it to ensure clean bisection.

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/verifier.c                         | 12 +++++-----
 .../testing/selftests/bpf/progs/dynptr_fail.c | 22 +++++++++----------
 .../selftests/bpf/progs/iters_state_safety.c  | 14 ++++++------
 .../selftests/bpf/progs/iters_testmod_seq.c   |  4 ++--
 .../bpf/progs/test_kfunc_dynptr_param.c       |  2 +-
 .../selftests/bpf/progs/verifier_bits_iter.c  |  4 ++--
 6 files changed, 29 insertions(+), 29 deletions(-)

Comments

Kumar Kartikeya Dwivedi Nov. 27, 2024, 11:06 p.m. UTC | #1 
On Thu, 28 Nov 2024 at 00:01, Kumar Kartikeya Dwivedi <memxor@gmail.com> wrote:
>
> Andrii spotted that process_dynptr_func's rejection of incorrect
> argument register type will print an error string where argument numbers
> are not zero-indexed, unlike elsewhere in the verifier.  Fix this by
> subtracting 1 from regno. The same scenario exists for iterator
> messages. Fix selftest error strings that match on the exact argument
> number while we're at it to ensure clean bisection.
>
> Suggested-by: Andrii Nakryiko <andrii@kernel.org>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> --

When working on this, I noticed the same situation exists in IRQ
save/restore v4.

There are several options:
1. If this lands after IRQ series, I can respin and fix regno use in
process_irq_flag.
2. Maintainer landing IRQ series can s/regno/regno - 1/ in
process_irq_flag, selftests don't match on argument number.
3. I can respin IRQ series v5 with this addressed now.
4. If this lands before IRQ series, I can respin IRQ series and make the fix.
5. It can be a follow up for IRQ series.

Let me know whichever seems better.
diff mbox series

Patch

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 358a3566bb60..2fd35465d650 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -8071,7 +8071,7 @@  static int process_dynptr_func(struct bpf_verifier_env *env, int regno, int insn
 	if (reg->type != PTR_TO_STACK && reg->type != CONST_PTR_TO_DYNPTR) {
 		verbose(env,
 			"arg#%d expected pointer to stack or const struct bpf_dynptr\n",
-			regno);
+			regno - 1);
 		return -EINVAL;
 	}
 
@@ -8125,7 +8125,7 @@  static int process_dynptr_func(struct bpf_verifier_env *env, int regno, int insn
 		if (!is_dynptr_reg_valid_init(env, reg)) {
 			verbose(env,
 				"Expected an initialized dynptr as arg #%d\n",
-				regno);
+				regno - 1);
 			return -EINVAL;
 		}
 
@@ -8133,7 +8133,7 @@  static int process_dynptr_func(struct bpf_verifier_env *env, int regno, int insn
 		if (!is_dynptr_type_expected(env, reg, arg_type & ~MEM_RDONLY)) {
 			verbose(env,
 				"Expected a dynptr of type %s as arg #%d\n",
-				dynptr_type_str(arg_to_dynptr_type(arg_type)), regno);
+				dynptr_type_str(arg_to_dynptr_type(arg_type)), regno - 1);
 			return -EINVAL;
 		}
 
@@ -8202,7 +8202,7 @@  static int process_iter_arg(struct bpf_verifier_env *env, int regno, int insn_id
 	 */
 	btf_id = btf_check_iter_arg(meta->btf, meta->func_proto, regno - 1);
 	if (btf_id < 0) {
-		verbose(env, "expected valid iter pointer as arg #%d\n", regno);
+		verbose(env, "expected valid iter pointer as arg #%d\n", regno - 1);
 		return -EINVAL;
 	}
 	t = btf_type_by_id(meta->btf, btf_id);
@@ -8212,7 +8212,7 @@  static int process_iter_arg(struct bpf_verifier_env *env, int regno, int insn_id
 		/* bpf_iter_<type>_new() expects pointer to uninit iter state */
 		if (!is_iter_reg_valid_uninit(env, reg, nr_slots)) {
 			verbose(env, "expected uninitialized iter_%s as arg #%d\n",
-				iter_type_str(meta->btf, btf_id), regno);
+				iter_type_str(meta->btf, btf_id), regno - 1);
 			return -EINVAL;
 		}
 
@@ -8236,7 +8236,7 @@  static int process_iter_arg(struct bpf_verifier_env *env, int regno, int insn_id
 			break;
 		case -EINVAL:
 			verbose(env, "expected an initialized iter_%s as arg #%d\n",
-				iter_type_str(meta->btf, btf_id), regno);
+				iter_type_str(meta->btf, btf_id), regno - 1);
 			return err;
 		case -EPROTO:
 			verbose(env, "expected an RCU CS when using %s\n", meta->func_name);
diff --git a/tools/testing/selftests/bpf/progs/dynptr_fail.c b/tools/testing/selftests/bpf/progs/dynptr_fail.c
index 8f36c9de7591..dfd817d0348c 100644
--- a/tools/testing/selftests/bpf/progs/dynptr_fail.c
+++ b/tools/testing/selftests/bpf/progs/dynptr_fail.c
@@ -149,7 +149,7 @@  int ringbuf_release_uninit_dynptr(void *ctx)
 
 /* A dynptr can't be used after it has been invalidated */
 SEC("?raw_tp")
-__failure __msg("Expected an initialized dynptr as arg #3")
+__failure __msg("Expected an initialized dynptr as arg #2")
 int use_after_invalid(void *ctx)
 {
 	struct bpf_dynptr ptr;
@@ -428,7 +428,7 @@  int invalid_helper2(void *ctx)
 
 /* A bpf_dynptr is invalidated if it's been written into */
 SEC("?raw_tp")
-__failure __msg("Expected an initialized dynptr as arg #1")
+__failure __msg("Expected an initialized dynptr as arg #0")
 int invalid_write1(void *ctx)
 {
 	struct bpf_dynptr ptr;
@@ -1407,7 +1407,7 @@  int invalid_slice_rdwr_rdonly(struct __sk_buff *skb)
 
 /* bpf_dynptr_adjust can only be called on initialized dynptrs */
 SEC("?raw_tp")
-__failure __msg("Expected an initialized dynptr as arg #1")
+__failure __msg("Expected an initialized dynptr as arg #0")
 int dynptr_adjust_invalid(void *ctx)
 {
 	struct bpf_dynptr ptr = {};
@@ -1420,7 +1420,7 @@  int dynptr_adjust_invalid(void *ctx)
 
 /* bpf_dynptr_is_null can only be called on initialized dynptrs */
 SEC("?raw_tp")
-__failure __msg("Expected an initialized dynptr as arg #1")
+__failure __msg("Expected an initialized dynptr as arg #0")
 int dynptr_is_null_invalid(void *ctx)
 {
 	struct bpf_dynptr ptr = {};
@@ -1433,7 +1433,7 @@  int dynptr_is_null_invalid(void *ctx)
 
 /* bpf_dynptr_is_rdonly can only be called on initialized dynptrs */
 SEC("?raw_tp")
-__failure __msg("Expected an initialized dynptr as arg #1")
+__failure __msg("Expected an initialized dynptr as arg #0")
 int dynptr_is_rdonly_invalid(void *ctx)
 {
 	struct bpf_dynptr ptr = {};
@@ -1446,7 +1446,7 @@  int dynptr_is_rdonly_invalid(void *ctx)
 
 /* bpf_dynptr_size can only be called on initialized dynptrs */
 SEC("?raw_tp")
-__failure __msg("Expected an initialized dynptr as arg #1")
+__failure __msg("Expected an initialized dynptr as arg #0")
 int dynptr_size_invalid(void *ctx)
 {
 	struct bpf_dynptr ptr = {};
@@ -1459,7 +1459,7 @@  int dynptr_size_invalid(void *ctx)
 
 /* Only initialized dynptrs can be cloned */
 SEC("?raw_tp")
-__failure __msg("Expected an initialized dynptr as arg #1")
+__failure __msg("Expected an initialized dynptr as arg #0")
 int clone_invalid1(void *ctx)
 {
 	struct bpf_dynptr ptr1 = {};
@@ -1493,7 +1493,7 @@  int clone_invalid2(struct xdp_md *xdp)
 
 /* Invalidating a dynptr should invalidate its clones */
 SEC("?raw_tp")
-__failure __msg("Expected an initialized dynptr as arg #3")
+__failure __msg("Expected an initialized dynptr as arg #2")
 int clone_invalidate1(void *ctx)
 {
 	struct bpf_dynptr clone;
@@ -1514,7 +1514,7 @@  int clone_invalidate1(void *ctx)
 
 /* Invalidating a dynptr should invalidate its parent */
 SEC("?raw_tp")
-__failure __msg("Expected an initialized dynptr as arg #3")
+__failure __msg("Expected an initialized dynptr as arg #2")
 int clone_invalidate2(void *ctx)
 {
 	struct bpf_dynptr ptr;
@@ -1535,7 +1535,7 @@  int clone_invalidate2(void *ctx)
 
 /* Invalidating a dynptr should invalidate its siblings */
 SEC("?raw_tp")
-__failure __msg("Expected an initialized dynptr as arg #3")
+__failure __msg("Expected an initialized dynptr as arg #2")
 int clone_invalidate3(void *ctx)
 {
 	struct bpf_dynptr ptr;
@@ -1723,7 +1723,7 @@  __noinline long global_call_bpf_dynptr(const struct bpf_dynptr *dynptr)
 }
 
 SEC("?raw_tp")
-__failure __msg("arg#1 expected pointer to stack or const struct bpf_dynptr")
+__failure __msg("arg#0 expected pointer to stack or const struct bpf_dynptr")
 int test_dynptr_reg_type(void *ctx)
 {
 	struct task_struct *current = NULL;
diff --git a/tools/testing/selftests/bpf/progs/iters_state_safety.c b/tools/testing/selftests/bpf/progs/iters_state_safety.c
index d47e59aba6de..f41257eadbb2 100644
--- a/tools/testing/selftests/bpf/progs/iters_state_safety.c
+++ b/tools/testing/selftests/bpf/progs/iters_state_safety.c
@@ -73,7 +73,7 @@  int create_and_forget_to_destroy_fail(void *ctx)
 }
 
 SEC("?raw_tp")
-__failure __msg("expected an initialized iter_num as arg #1")
+__failure __msg("expected an initialized iter_num as arg #0")
 int destroy_without_creating_fail(void *ctx)
 {
 	/* init with zeros to stop verifier complaining about uninit stack */
@@ -91,7 +91,7 @@  int destroy_without_creating_fail(void *ctx)
 }
 
 SEC("?raw_tp")
-__failure __msg("expected an initialized iter_num as arg #1")
+__failure __msg("expected an initialized iter_num as arg #0")
 int compromise_iter_w_direct_write_fail(void *ctx)
 {
 	struct bpf_iter_num iter;
@@ -143,7 +143,7 @@  int compromise_iter_w_direct_write_and_skip_destroy_fail(void *ctx)
 }
 
 SEC("?raw_tp")
-__failure __msg("expected an initialized iter_num as arg #1")
+__failure __msg("expected an initialized iter_num as arg #0")
 int compromise_iter_w_helper_write_fail(void *ctx)
 {
 	struct bpf_iter_num iter;
@@ -230,7 +230,7 @@  int valid_stack_reuse(void *ctx)
 }
 
 SEC("?raw_tp")
-__failure __msg("expected uninitialized iter_num as arg #1")
+__failure __msg("expected uninitialized iter_num as arg #0")
 int double_create_fail(void *ctx)
 {
 	struct bpf_iter_num iter;
@@ -258,7 +258,7 @@  int double_create_fail(void *ctx)
 }
 
 SEC("?raw_tp")
-__failure __msg("expected an initialized iter_num as arg #1")
+__failure __msg("expected an initialized iter_num as arg #0")
 int double_destroy_fail(void *ctx)
 {
 	struct bpf_iter_num iter;
@@ -284,7 +284,7 @@  int double_destroy_fail(void *ctx)
 }
 
 SEC("?raw_tp")
-__failure __msg("expected an initialized iter_num as arg #1")
+__failure __msg("expected an initialized iter_num as arg #0")
 int next_without_new_fail(void *ctx)
 {
 	struct bpf_iter_num iter;
@@ -305,7 +305,7 @@  int next_without_new_fail(void *ctx)
 }
 
 SEC("?raw_tp")
-__failure __msg("expected an initialized iter_num as arg #1")
+__failure __msg("expected an initialized iter_num as arg #0")
 int next_after_destroy_fail(void *ctx)
 {
 	struct bpf_iter_num iter;
diff --git a/tools/testing/selftests/bpf/progs/iters_testmod_seq.c b/tools/testing/selftests/bpf/progs/iters_testmod_seq.c
index 4a176e6aede8..6543d5b6e0a9 100644
--- a/tools/testing/selftests/bpf/progs/iters_testmod_seq.c
+++ b/tools/testing/selftests/bpf/progs/iters_testmod_seq.c
@@ -79,7 +79,7 @@  int testmod_seq_truncated(const void *ctx)
 
 SEC("?raw_tp")
 __failure
-__msg("expected an initialized iter_testmod_seq as arg #2")
+__msg("expected an initialized iter_testmod_seq as arg #1")
 int testmod_seq_getter_before_bad(const void *ctx)
 {
 	struct bpf_iter_testmod_seq it;
@@ -89,7 +89,7 @@  int testmod_seq_getter_before_bad(const void *ctx)
 
 SEC("?raw_tp")
 __failure
-__msg("expected an initialized iter_testmod_seq as arg #2")
+__msg("expected an initialized iter_testmod_seq as arg #1")
 int testmod_seq_getter_after_bad(const void *ctx)
 {
 	struct bpf_iter_testmod_seq it;
diff --git a/tools/testing/selftests/bpf/progs/test_kfunc_dynptr_param.c b/tools/testing/selftests/bpf/progs/test_kfunc_dynptr_param.c
index e68667aec6a6..cd4d752bd089 100644
--- a/tools/testing/selftests/bpf/progs/test_kfunc_dynptr_param.c
+++ b/tools/testing/selftests/bpf/progs/test_kfunc_dynptr_param.c
@@ -45,7 +45,7 @@  int BPF_PROG(not_valid_dynptr, int cmd, union bpf_attr *attr, unsigned int size)
 }
 
 SEC("?lsm.s/bpf")
-__failure __msg("arg#1 expected pointer to stack or const struct bpf_dynptr")
+__failure __msg("arg#0 expected pointer to stack or const struct bpf_dynptr")
 int BPF_PROG(not_ptr_to_stack, int cmd, union bpf_attr *attr, unsigned int size)
 {
 	unsigned long val = 0;
diff --git a/tools/testing/selftests/bpf/progs/verifier_bits_iter.c b/tools/testing/selftests/bpf/progs/verifier_bits_iter.c
index a7a6ae6c162f..8bcddadfc4da 100644
--- a/tools/testing/selftests/bpf/progs/verifier_bits_iter.c
+++ b/tools/testing/selftests/bpf/progs/verifier_bits_iter.c
@@ -32,7 +32,7 @@  int BPF_PROG(no_destroy, struct bpf_iter_meta *meta, struct cgroup *cgrp)
 
 SEC("iter/cgroup")
 __description("uninitialized iter in ->next()")
-__failure __msg("expected an initialized iter_bits as arg #1")
+__failure __msg("expected an initialized iter_bits as arg #0")
 int BPF_PROG(next_uninit, struct bpf_iter_meta *meta, struct cgroup *cgrp)
 {
 	struct bpf_iter_bits it = {};
@@ -43,7 +43,7 @@  int BPF_PROG(next_uninit, struct bpf_iter_meta *meta, struct cgroup *cgrp)
 
 SEC("iter/cgroup")
 __description("uninitialized iter in ->destroy()")
-__failure __msg("expected an initialized iter_bits as arg #1")
+__failure __msg("expected an initialized iter_bits as arg #0")
 int BPF_PROG(destroy_uninit, struct bpf_iter_meta *meta, struct cgroup *cgrp)
 {
 	struct bpf_iter_bits it = {};