Commit 10aceb62 authored by Dave Marchevsky's avatar Dave Marchevsky Committed by Alexei Starovoitov
Browse files

bpf: Add bpf_trace_vprintk helper 

This helper is meant to be "bpf_trace_printk, but with proper vararg
support". Follow bpf_snprintf's example and take a u64 pseudo-vararg
array. Write to /sys/kernel/debug/tracing/trace_pipe using the same
mechanism as bpf_trace_printk. The functionality of this helper was
requested in the libbpf issue tracker [0].

[0] Closes: https://github.com/libbpf/libbpf/issues/315



Signed-off-by: default avatarDave Marchevsky <davemarchevsky@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210917182911.2426606-4-davemarchevsky@fb.com
parent 84b4c529

include/linux/bpf.h

+1 −0
Original line number Diff line number Diff line
@@ -1088,6 +1088,7 @@ bool bpf_prog_array_compatible(struct bpf_array *array, const struct bpf_prog *f 
int bpf_prog_calc_tag(struct bpf_prog *fp);



const struct bpf_func_proto *bpf_get_trace_printk_proto(void);

const struct bpf_func_proto *bpf_get_trace_vprintk_proto(void);



typedef unsigned long (*bpf_ctx_copy_t)(void *dst, const void *src,

					unsigned long off, unsigned long len);

include/uapi/linux/bpf.h

+11 −0
Original line number Diff line number Diff line
@@ -4898,6 +4898,16 @@ union bpf_attr { 
 *		**-EINVAL** if *flags* is not zero.

 *

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

 *

 * long bpf_trace_vprintk(const char *fmt, u32 fmt_size, const void *data, u32 data_len)

 *	Description

 *		Behaves like **bpf_trace_printk**\ () helper, but takes an array of u64

 *		to format and can handle more format args as a result.

 *

 *		Arguments are to be used as in **bpf_seq_printf**\ () helper.

 *	Return

 *		The number of bytes written to the buffer, or a negative error

 *		in case of failure.

 */

#define __BPF_FUNC_MAPPER(FN)		\

	FN(unspec),			\
@@ -5077,6 +5087,7 @@ union bpf_attr { 
	FN(get_attach_cookie),		\

	FN(task_pt_regs),		\

	FN(get_branch_snapshot),	\

	FN(trace_vprintk),		\

	/* */



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

kernel/bpf/core.c

+5 −0
Original line number Diff line number Diff line
@@ -2357,6 +2357,11 @@ const struct bpf_func_proto * __weak bpf_get_trace_printk_proto(void) 
	return NULL;

}



const struct bpf_func_proto * __weak bpf_get_trace_vprintk_proto(void)

{

	return NULL;

}



u64 __weak

bpf_event_output(struct bpf_map *map, u64 flags, void *meta, u64 meta_size,

		 void *ctx, u64 ctx_size, bpf_ctx_copy_t ctx_copy)

kernel/bpf/helpers.c

+2 −0
Original line number Diff line number Diff line
@@ -1435,6 +1435,8 @@ bpf_base_func_proto(enum bpf_func_id func_id) 
		return &bpf_snprintf_proto;

	case BPF_FUNC_task_pt_regs:

		return &bpf_task_pt_regs_proto;

	case BPF_FUNC_trace_vprintk:

		return bpf_get_trace_vprintk_proto();

	default:

		return NULL;

	}

kernel/trace/bpf_trace.c

+51 −1
Original line number Diff line number Diff line
@@ -398,7 +398,7 @@ static const struct bpf_func_proto bpf_trace_printk_proto = { 
	.arg2_type	= ARG_CONST_SIZE,

};



const struct bpf_func_proto *bpf_get_trace_printk_proto(void)

static void __set_printk_clr_event(void)

{

	/*

	 * This program might be calling bpf_trace_printk,
@@ -410,10 +410,58 @@ const struct bpf_func_proto *bpf_get_trace_printk_proto(void) 
	 */

	if (trace_set_clr_event("bpf_trace", "bpf_trace_printk", 1))

		pr_warn_ratelimited("could not enable bpf_trace_printk events");

}



const struct bpf_func_proto *bpf_get_trace_printk_proto(void)

{

	__set_printk_clr_event();

	return &bpf_trace_printk_proto;

}



BPF_CALL_4(bpf_trace_vprintk, char *, fmt, u32, fmt_size, const void *, data,

	   u32, data_len)

{

	static char buf[BPF_TRACE_PRINTK_SIZE];

	unsigned long flags;

	int ret, num_args;

	u32 *bin_args;



	if (data_len & 7 || data_len > MAX_BPRINTF_VARARGS * 8 ||

	    (data_len && !data))

		return -EINVAL;

	num_args = data_len / 8;



	ret = bpf_bprintf_prepare(fmt, fmt_size, data, &bin_args, num_args);

	if (ret < 0)

		return ret;



	raw_spin_lock_irqsave(&trace_printk_lock, flags);

	ret = bstr_printf(buf, sizeof(buf), fmt, bin_args);



	trace_bpf_trace_printk(buf);

	raw_spin_unlock_irqrestore(&trace_printk_lock, flags);



	bpf_bprintf_cleanup();



	return ret;

}



static const struct bpf_func_proto bpf_trace_vprintk_proto = {

	.func		= bpf_trace_vprintk,

	.gpl_only	= true,

	.ret_type	= RET_INTEGER,

	.arg1_type	= ARG_PTR_TO_MEM,

	.arg2_type	= ARG_CONST_SIZE,

	.arg3_type	= ARG_PTR_TO_MEM_OR_NULL,

	.arg4_type	= ARG_CONST_SIZE_OR_ZERO,

};



const struct bpf_func_proto *bpf_get_trace_vprintk_proto(void)

{

	__set_printk_clr_event();

	return &bpf_trace_vprintk_proto;

}



BPF_CALL_5(bpf_seq_printf, struct seq_file *, m, char *, fmt, u32, fmt_size,

	   const void *, data, u32, data_len)

{
@@ -1160,6 +1208,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) 
		return &bpf_get_func_ip_proto_tracing;

	case BPF_FUNC_get_branch_snapshot:

		return &bpf_get_branch_snapshot_proto;

	case BPF_FUNC_trace_vprintk:

		return bpf_get_trace_vprintk_proto();

	default:

		return bpf_base_func_proto(func_id);

	}