Commit 856c02db authored by Song Liu's avatar Song Liu Committed by Alexei Starovoitov
Browse files

bpf: Introduce helper bpf_get_branch_snapshot 



Introduce bpf_get_branch_snapshot(), which allows tracing pogram to get
branch trace from hardware (e.g. Intel LBR). To use the feature, the
user need to create perf_event with proper branch_record filtering
on each cpu, and then calls bpf_get_branch_snapshot in the bpf function.
On Intel CPUs, VLBR event (raw event 0x1b00) can be use for this.

Signed-off-by: default avatarSong Liu <songliubraving@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Acked-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210910183352.3151445-3-songliubraving@fb.com
parent c22ac2a3

include/uapi/linux/bpf.h

+22 −0
Original line number Diff line number Diff line
@@ -4877,6 +4877,27 @@ union bpf_attr { 
 *		Get the struct pt_regs associated with **task**.

 *	Return

 *		A pointer to struct pt_regs.

 *

 * long bpf_get_branch_snapshot(void *entries, u32 size, u64 flags)

 *	Description

 *		Get branch trace from hardware engines like Intel LBR. The

 *		hardware engine is stopped shortly after the helper is

 *		called. Therefore, the user need to filter branch entries

 *		based on the actual use case. To capture branch trace

 *		before the trigger point of the BPF program, the helper

 *		should be called at the beginning of the BPF program.

 *

 *		The data is stored as struct perf_branch_entry into output

 *		buffer *entries*. *size* is the size of *entries* in bytes.

 *		*flags* is reserved for now and must be zero.

 *

 *	Return

 *		On success, number of bytes written to *buf*. On error, a

 *		negative value.

 *

 *		**-EINVAL** if *flags* is not zero.

 *

 *		**-ENOENT** if architecture does not support branch records.

 */

#define __BPF_FUNC_MAPPER(FN)		\

	FN(unspec),			\
@@ -5055,6 +5076,7 @@ union bpf_attr { 
	FN(get_func_ip),		\

	FN(get_attach_cookie),		\

	FN(task_pt_regs),		\

	FN(get_branch_snapshot),	\

	/* */



/* integer value in 'imm' field of BPF_CALL instruction selects which helper

kernel/bpf/trampoline.c

+2 −1
Original line number Diff line number Diff line
@@ -10,6 +10,7 @@ 
#include <linux/rcupdate_trace.h>

#include <linux/rcupdate_wait.h>

#include <linux/module.h>

#include <linux/static_call.h>



/* dummy _ops. The verifier will operate on target program's ops. */

const struct bpf_verifier_ops bpf_extension_verifier_ops = {
@@ -526,7 +527,7 @@ void bpf_trampoline_put(struct bpf_trampoline *tr) 
}



#define NO_START_TIME 1

static u64 notrace bpf_prog_start_time(void)

static __always_inline u64 notrace bpf_prog_start_time(void)

{

	u64 start = NO_START_TIME;

kernel/trace/bpf_trace.c

+30 −0
Original line number Diff line number Diff line
@@ -1017,6 +1017,34 @@ static const struct bpf_func_proto bpf_get_attach_cookie_proto_pe = { 
	.arg1_type	= ARG_PTR_TO_CTX,

};



BPF_CALL_3(bpf_get_branch_snapshot, void *, buf, u32, size, u64, flags)

{

#ifndef CONFIG_X86

	return -ENOENT;

#else

	static const u32 br_entry_size = sizeof(struct perf_branch_entry);

	u32 entry_cnt = size / br_entry_size;



	entry_cnt = static_call(perf_snapshot_branch_stack)(buf, entry_cnt);



	if (unlikely(flags))

		return -EINVAL;



	if (!entry_cnt)

		return -ENOENT;



	return entry_cnt * br_entry_size;

#endif

}



static const struct bpf_func_proto bpf_get_branch_snapshot_proto = {

	.func		= bpf_get_branch_snapshot,

	.gpl_only	= true,

	.ret_type	= RET_INTEGER,

	.arg1_type	= ARG_PTR_TO_UNINIT_MEM,

	.arg2_type	= ARG_CONST_SIZE_OR_ZERO,

};



static const struct bpf_func_proto *

bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)

{
@@ -1132,6 +1160,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) 
		return &bpf_snprintf_proto;

	case BPF_FUNC_get_func_ip:

		return &bpf_get_func_ip_proto_tracing;

	case BPF_FUNC_get_branch_snapshot:

		return &bpf_get_branch_snapshot_proto;

	default:

		return bpf_base_func_proto(func_id);

	}

tools/include/uapi/linux/bpf.h

+22 −0
Original line number Diff line number Diff line
@@ -4877,6 +4877,27 @@ union bpf_attr { 
 *		Get the struct pt_regs associated with **task**.

 *	Return

 *		A pointer to struct pt_regs.

 *

 * long bpf_get_branch_snapshot(void *entries, u32 size, u64 flags)

 *	Description

 *		Get branch trace from hardware engines like Intel LBR. The

 *		hardware engine is stopped shortly after the helper is

 *		called. Therefore, the user need to filter branch entries

 *		based on the actual use case. To capture branch trace

 *		before the trigger point of the BPF program, the helper

 *		should be called at the beginning of the BPF program.

 *

 *		The data is stored as struct perf_branch_entry into output

 *		buffer *entries*. *size* is the size of *entries* in bytes.

 *		*flags* is reserved for now and must be zero.

 *

 *	Return

 *		On success, number of bytes written to *buf*. On error, a

 *		negative value.

 *

 *		**-EINVAL** if *flags* is not zero.

 *

 *		**-ENOENT** if architecture does not support branch records.

 */

#define __BPF_FUNC_MAPPER(FN)		\

	FN(unspec),			\
@@ -5055,6 +5076,7 @@ union bpf_attr { 
	FN(get_func_ip),		\

	FN(get_attach_cookie),		\

	FN(task_pt_regs),		\

	FN(get_branch_snapshot),	\

	/* */



/* integer value in 'imm' field of BPF_CALL instruction selects which helper