This helper is only used by BPF program attached to perf_event. If the
perf_event has PEBS entries, calling get_perf_callchain from BPF program
may cause unwinder errors. bpf_get_callchain_stackid serves as alternative
to bpf_get_stackid for these BPF programs.
Signed-off-by: Song Liu <songliubrav...@fb.com>
---
include/linux/bpf.h | 1 +
include/uapi/linux/bpf.h | 43 +++++++++++++++++++++++
kernel/bpf/stackmap.c | 63 ++++++++++++++++++++++++++--------
kernel/bpf/verifier.c | 4 ++-
kernel/trace/bpf_trace.c | 2 ++
scripts/bpf_helpers_doc.py | 2 ++
tools/include/uapi/linux/bpf.h | 43 +++++++++++++++++++++++
7 files changed, 142 insertions(+), 16 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 0cd7f6884c5cd..45cf12acb0e26 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1628,6 +1628,7 @@ extern const struct bpf_func_proto
bpf_get_current_comm_proto;
extern const struct bpf_func_proto bpf_get_stackid_proto;
extern const struct bpf_func_proto bpf_get_stack_proto;
extern const struct bpf_func_proto bpf_get_task_stack_proto;
+extern const struct bpf_func_proto bpf_get_callchain_stackid_proto;
extern const struct bpf_func_proto bpf_sock_map_update_proto;
extern const struct bpf_func_proto bpf_sock_hash_update_proto;
extern const struct bpf_func_proto bpf_get_current_cgroup_id_proto;
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 548a749aebb3e..a808accfbd457 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -3319,6 +3319,48 @@ union bpf_attr {
* A non-negative value equal to or less than *size* on success,
* or a negative error in case of failure.
*
+ * long bpf_get_callchain_stackid(struct perf_callchain_entry *callchain,
struct bpf_map *map, u64 flags)
+ * Description
+ * Walk a user or a kernel stack and return its id. To achieve
+ * this, the helper needs *callchain*, which is a pointer to a
+ * valid perf_callchain_entry, and a pointer to a *map* of type
+ * **BPF_MAP_TYPE_STACK_TRACE**.
+ *
+ * The last argument, *flags*, holds the number of stack frames to
+ * skip (from 0 to 255), masked with
+ * **BPF_F_SKIP_FIELD_MASK**. The next bits can be used to set
+ * a combination of the following flags:
+ *
+ * **BPF_F_USER_STACK**
+ * Collect a user space stack instead of a kernel stack.
+ * **BPF_F_FAST_STACK_CMP**
+ * Compare stacks by hash only.
+ * **BPF_F_REUSE_STACKID**
+ * If two different stacks hash into the same *stackid*,
+ * discard the old one.
+ *
+ * The stack id retrieved is a 32 bit long integer handle which
+ * can be further combined with other data (including other stack
+ * ids) and used as a key into maps. This can be useful for
+ * generating a variety of graphs (such as flame graphs or off-cpu
+ * graphs).
+ *
+ * For walking a stack, this helper is an improvement over
+ * **bpf_probe_read**\ (), which can be used with unrolled loops
+ * but is not efficient and consumes a lot of eBPF instructions.
+ * Instead, **bpf_get_callchain_stackid**\ () can collect up to
+ * **PERF_MAX_STACK_DEPTH** both kernel and user frames. Note that
+ * this limit can be controlled with the **sysctl** program, and
+ * that it should be manually increased in order to profile long
+ * user stacks (such as stacks for Java programs). To do so, use:
+ *
+ * ::
+ *
+ * # sysctl kernel.perf_event_max_stack=<new value>
+ * Return
+ * The positive or null stack id on success, or a negative error
+ * in case of failure.
+ *
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -3463,6 +3505,7 @@ union bpf_attr {
FN(skc_to_tcp_request_sock), \
FN(skc_to_udp6_sock), \
FN(get_task_stack), \
+ FN(get_callchain_stackid), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index a6c361ed7937b..28acc610f7f94 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -386,11 +386,10 @@ get_callchain_entry_for_task(struct task_struct *task,
u32 init_nr)
#endif
}
-BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
- u64, flags)
+static long __bpf_get_stackid(struct bpf_map *map, struct perf_callchain_entry
*trace,
+ u64 flags)
{
struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map,
map);
- struct perf_callchain_entry *trace;
struct stack_map_bucket *bucket, *new_bucket, *old_bucket;
u32 max_depth = map->value_size / stack_map_data_size(map);
/* stack_map_alloc() checks that max_depth <=
sysctl_perf_event_max_stack */
@@ -398,21 +397,9 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct
bpf_map *, map,
u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
u32 hash, id, trace_nr, trace_len;
bool user = flags & BPF_F_USER_STACK;
- bool kernel = !user;
u64 *ips;
bool hash_matches;
- if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
- BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID)))
- return -EINVAL;
-
- trace = get_perf_callchain(regs, init_nr, kernel, user,
- sysctl_perf_event_max_stack, false, false);
-
- if (unlikely(!trace))
- /* couldn't fetch the stack trace */
- return -EFAULT;
-
/* get_perf_callchain() guarantees that trace->nr >= init_nr
* and trace-nr <= sysctl_perf_event_max_stack, so trace_nr <= max_depth
*/
@@ -477,6 +464,30 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct
bpf_map *, map,
return id;
}
+BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
+ u64, flags)
+{
+ u32 max_depth = map->value_size / stack_map_data_size(map);
+ /* stack_map_alloc() checks that max_depth <=
sysctl_perf_event_max_stack */
+ u32 init_nr = sysctl_perf_event_max_stack - max_depth;
+ bool user = flags & BPF_F_USER_STACK;
+ struct perf_callchain_entry *trace;
+ bool kernel = !user;
+
+ if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
+ BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID)))
+ return -EINVAL;
+
+ trace = get_perf_callchain(regs, init_nr, kernel, user,
+ sysctl_perf_event_max_stack, false, false);
+
+ if (unlikely(!trace))
+ /* couldn't fetch the stack trace */
+ return -EFAULT;
+
+ return __bpf_get_stackid(map, trace, flags);
+}
+
const struct bpf_func_proto bpf_get_stackid_proto = {
.func = bpf_get_stackid,
.gpl_only = true,
@@ -486,6 +497,28 @@ const struct bpf_func_proto bpf_get_stackid_proto = {
.arg3_type = ARG_ANYTHING,
};
+BPF_CALL_3(bpf_get_callchain_stackid, struct perf_callchain_entry *, callchain,
+ struct bpf_map *, map, u64, flags)
+{
+ if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
+ BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID)))
+ return -EINVAL;
+ if (!callchain)
+ return -EFAULT;
+ return __bpf_get_stackid(map, callchain, flags);
+}
+
+static int bpf_get_callchain_stackid_btf_ids[5];
+const struct bpf_func_proto bpf_get_callchain_stackid_proto = {
+ .func = bpf_get_callchain_stackid,
+ .gpl_only = false,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_PTR_TO_BTF_ID,
+ .arg2_type = ARG_CONST_MAP_PTR,
+ .arg3_type = ARG_ANYTHING,
+ .btf_id = bpf_get_callchain_stackid_btf_ids,
+};
+
static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
void *buf, u32 size, u64 flags)
{
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 1e11b0f6fba31..07be75550ca93 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4094,7 +4094,8 @@ static int check_map_func_compatibility(struct
bpf_verifier_env *env,
goto error;
break;
case BPF_MAP_TYPE_STACK_TRACE:
- if (func_id != BPF_FUNC_get_stackid)
+ if (func_id != BPF_FUNC_get_stackid &&
+ func_id != BPF_FUNC_get_callchain_stackid)
goto error;
break;
case BPF_MAP_TYPE_CGROUP_ARRAY:
@@ -4187,6 +4188,7 @@ static int check_map_func_compatibility(struct
bpf_verifier_env *env,
goto error;
break;
case BPF_FUNC_get_stackid:
+ case BPF_FUNC_get_callchain_stackid:
if (map->map_type != BPF_MAP_TYPE_STACK_TRACE)
goto error;
break;
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index c014846c2723c..7a504f734a025 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1396,6 +1396,8 @@ pe_prog_func_proto(enum bpf_func_id func_id, const struct
bpf_prog *prog)
return &bpf_perf_prog_read_value_proto;
case BPF_FUNC_read_branch_records:
return &bpf_read_branch_records_proto;
+ case BPF_FUNC_get_callchain_stackid:
+ return &bpf_get_callchain_stackid_proto;
default:
return bpf_tracing_func_proto(func_id, prog);
}
diff --git a/scripts/bpf_helpers_doc.py b/scripts/bpf_helpers_doc.py
index 6843376733df8..1b99e3618e492 100755
--- a/scripts/bpf_helpers_doc.py
+++ b/scripts/bpf_helpers_doc.py
@@ -427,6 +427,7 @@ class PrinterHelpers(Printer):
'struct tcp_request_sock',
'struct udp6_sock',
'struct task_struct',
+ 'struct perf_callchain_entry',
'struct __sk_buff',
'struct sk_msg_md',
@@ -470,6 +471,7 @@ class PrinterHelpers(Printer):
'struct tcp_request_sock',
'struct udp6_sock',
'struct task_struct',
+ 'struct perf_callchain_entry',
}
mapped_types = {
'u8': '__u8',
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 548a749aebb3e..a808accfbd457 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -3319,6 +3319,48 @@ union bpf_attr {
* A non-negative value equal to or less than *size* on success,
* or a negative error in case of failure.
*
+ * long bpf_get_callchain_stackid(struct perf_callchain_entry *callchain,
struct bpf_map *map, u64 flags)
+ * Description
+ * Walk a user or a kernel stack and return its id. To achieve
+ * this, the helper needs *callchain*, which is a pointer to a
+ * valid perf_callchain_entry, and a pointer to a *map* of type
+ * **BPF_MAP_TYPE_STACK_TRACE**.
+ *
+ * The last argument, *flags*, holds the number of stack frames to
+ * skip (from 0 to 255), masked with
+ * **BPF_F_SKIP_FIELD_MASK**. The next bits can be used to set
+ * a combination of the following flags:
+ *
+ * **BPF_F_USER_STACK**
+ * Collect a user space stack instead of a kernel stack.
+ * **BPF_F_FAST_STACK_CMP**
+ * Compare stacks by hash only.
+ * **BPF_F_REUSE_STACKID**
+ * If two different stacks hash into the same *stackid*,
+ * discard the old one.
+ *
+ * The stack id retrieved is a 32 bit long integer handle which
+ * can be further combined with other data (including other stack
+ * ids) and used as a key into maps. This can be useful for
+ * generating a variety of graphs (such as flame graphs or off-cpu
+ * graphs).
+ *
+ * For walking a stack, this helper is an improvement over
+ * **bpf_probe_read**\ (), which can be used with unrolled loops
+ * but is not efficient and consumes a lot of eBPF instructions.
+ * Instead, **bpf_get_callchain_stackid**\ () can collect up to
+ * **PERF_MAX_STACK_DEPTH** both kernel and user frames. Note that
+ * this limit can be controlled with the **sysctl** program, and
+ * that it should be manually increased in order to profile long
+ * user stacks (such as stacks for Java programs). To do so, use:
+ *
+ * ::
+ *
+ * # sysctl kernel.perf_event_max_stack=<new value>
+ * Return
+ * The positive or null stack id on success, or a negative error
+ * in case of failure.
+ *
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -3463,6 +3505,7 @@ union bpf_attr {
FN(skc_to_tcp_request_sock), \
FN(skc_to_udp6_sock), \
FN(get_task_stack), \
+ FN(get_callchain_stackid), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
--
2.24.1
