Date:   Wed, 26 Apr 2023 08:55:20 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Alan Maguire <alan.maguire@...cle.com>
Cc:     linux-trace-kernel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        Florent Revest <revest@...omium.org>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Martin KaFai Lau <martin.lau@...ux.dev>, bpf@...r.kernel.org
Subject: Re: [PATCH v6 06/10] tracing/probes: Support function parameters if
 BTF is available

On Tue, 25 Apr 2023 17:35:34 +0100
Alan Maguire <alan.maguire@...cle.com> wrote:

> On 24/04/2023 15:46, Masami Hiramatsu (Google) wrote:
> > From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> > 
> > Support function or tracepoint parameters by name if BTF support is enabled
> > and the event is for function entry (this feature can be used with kprobe-
> > events, fprobe-events and tracepoint probe events.)
> > 
> > Note that the BTF variable syntax does not require a prefix. If it starts
> > with an alphabetic character or an underscore ('_') without a prefix like
> > '$' and '%', it is considered as a BTF variable.
> > If you specify only the BTF variable name, the argument name will also
> > be the same name instead of 'arg*'.
> > 
> >  # echo 'p vfs_read count pos' >> dynamic_events
> >  # echo 'f vfs_write count pos' >> dynamic_events
> >  # echo 't sched_overutilized_tp rd overutilized' >> dynamic_events
> >  # cat dynamic_events
> > p:kprobes/p_vfs_read_0 vfs_read count=count pos=pos
> > f:fprobes/vfs_write__entry vfs_write count=count pos=pos
> > t:tracepoints/sched_overutilized_tp sched_overutilized_tp rd=rd overutilized=overutilized
> > 
> > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> 
> A few small things below, but
> 
> Reviewed-by: Alan Maguire <alan.maguire@...cle.com>
> 
> Feel free to add a
> 
> Tested-by: Alan Maguire <alan.maguire@...cle.com>

Thank you for the review! let me see.

> 
> ...for the series (tested on x86_64; also built on
> aarch64 but because of (I presume) lack of 
> DYNAMIC_FTRACE_WITH_REGS, CONFIG_FPROBE could not
> be selected there.
> 
> > ---
> > Changes in v6:
> >  - update patch description.
> >  - use bpf_get_btf_vmlinux() instead of btf_parse_vmlinux().
> > ---
> >  kernel/trace/Kconfig        |   11 +++
> >  kernel/trace/trace.c        |    4 +
> >  kernel/trace/trace_fprobe.c |   49 +++++++----
> >  kernel/trace/trace_kprobe.c |   12 +--
> >  kernel/trace/trace_probe.c  |  184 +++++++++++++++++++++++++++++++++++++++++++
> >  kernel/trace/trace_probe.h  |    9 ++
> >  6 files changed, 240 insertions(+), 29 deletions(-)
> > 
> > diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> > index 8e10a9453c96..e2b415b9fcd4 100644
> > --- a/kernel/trace/Kconfig
> > +++ b/kernel/trace/Kconfig
> > @@ -664,6 +664,17 @@ config FPROBE_EVENTS
> >  	  and the kprobe events on function entry and exit will be
> >  	  transparently converted to this fprobe events.
> >  
> > +config PROBE_EVENTS_BTF_ARGS
> > +	depends on HAVE_FUNCTION_ARG_ACCESS_API
> > +	depends on FPROBE_EVENTS || KPROBE_EVENTS
> > +	depends on DEBUG_INFO_BTF && BPF_SYSCALL
> > +	bool "Support BTF function arguments for probe events"
> > +	default y
> > +	help
> > +	  The user can specify the arguments of the probe event using the names
> > +	  of the arguments of the probed function. This feature only works if
> > +	  the probe location is a kernel function entry or a tracepoint.
> > +
> >  config KPROBE_EVENTS
> >  	depends on KPROBES
> >  	depends on HAVE_REGS_AND_STACK_ACCESS_API
> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > index 9da9c979faa3..0d9c48197a5c 100644
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -5670,7 +5670,11 @@ static const char readme_msg[] =
> >  	"\t     args: <name>=fetcharg[:type]\n"
> >  	"\t fetcharg: (%<register>|$<efield>), @<address>, @<symbol>[+|-<offset>],\n"
> >  #ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API
> > +#ifdef CONFIG_PROBE_EVENTS_BTF_ARGS
> > +	"\t           $stack<index>, $stack, $retval, $comm, $arg<N>, <argname>\n"
> > +#else
> >  	"\t           $stack<index>, $stack, $retval, $comm, $arg<N>,\n"
> > +#endif
> >  #else
> >  	"\t           $stack<index>, $stack, $retval, $comm,\n"
> >  #endif
> > diff --git a/kernel/trace/trace_fprobe.c b/kernel/trace/trace_fprobe.c
> > index 1dba45dfd234..a34081113fa8 100644
> > --- a/kernel/trace/trace_fprobe.c
> > +++ b/kernel/trace/trace_fprobe.c
> > @@ -367,6 +367,7 @@ static void free_trace_fprobe(struct trace_fprobe *tf)
> >  static struct trace_fprobe *alloc_trace_fprobe(const char *group,
> >  					       const char *event,
> >  					       const char *symbol,
> > +					       struct tracepoint *tpoint,
> >  					       int maxactive,
> >  					       int nargs, bool is_return)
> >  {
> > @@ -386,6 +387,7 @@ static struct trace_fprobe *alloc_trace_fprobe(const char *group,
> >  	else
> >  		tf->fp.entry_handler = fentry_dispatcher;
> >  
> > +	tf->tpoint = tpoint;
> >  	tf->fp.nr_maxactive = maxactive;
> >  
> >  	ret = trace_probe_init(&tf->tp, event, group, false);
> > @@ -929,8 +931,12 @@ static int __trace_fprobe_create(int argc, const char *argv[])
> >  	int maxactive = 0;
> >  	char buf[MAX_EVENT_NAME_LEN];
> >  	char gbuf[MAX_EVENT_NAME_LEN];
> > -	unsigned int flags = TPARG_FL_KERNEL;
> > +	char sbuf[KSYM_NAME_LEN];
> >  	bool is_tracepoint = false;
> > +	struct tracepoint *tpoint = NULL;
> > +	struct traceprobe_parse_context ctx = {
> > +		.flags = TPARG_FL_KERNEL | TPARG_FL_FENTRY,
> > +	};
> >  
> >  	if ((argv[0][0] != 'f' && argv[0][0] != 't') || argc < 2)
> >  		return -ECANCELED;
> > @@ -994,12 +1000,6 @@ static int __trace_fprobe_create(int argc, const char *argv[])
> >  		goto parse_error;
> >  	}
> >  
> > -	flags |= TPARG_FL_FENTRY;
> > -	if (is_return)
> > -		flags |= TPARG_FL_RETURN;
> > -	if (is_tracepoint)
> > -		flags |= TPARG_FL_TPOINT;
> > -
> >  	trace_probe_log_set_index(0);
> >  	if (event) {
> >  		ret = traceprobe_parse_event_name(&event, &group, gbuf,
> > @@ -1011,7 +1011,8 @@ static int __trace_fprobe_create(int argc, const char *argv[])
> >  	if (!event) {
> >  		/* Make a new event name */
> >  		if (is_tracepoint)
> > -			strscpy(buf, symbol, MAX_EVENT_NAME_LEN);
> > +			snprintf(buf, MAX_EVENT_NAME_LEN, "%s%s",
> > +				 isdigit(*symbol) ? "_" : "", symbol);
> >  		else
> >  			snprintf(buf, MAX_EVENT_NAME_LEN, "%s__%s", symbol,
> >  				 is_return ? "exit" : "entry");
> > @@ -1019,8 +1020,25 @@ static int __trace_fprobe_create(int argc, const char *argv[])
> >  		event = buf;
> >  	}
> >  
> > +	if (is_return)
> > +		ctx.flags |= TPARG_FL_RETURN;
> > +
> > +	if (is_tracepoint) {
> > +		ctx.flags |= TPARG_FL_TPOINT;
> > +		tpoint = find_tracepoint(symbol);
> > +		if (!tpoint) {
> > +			trace_probe_log_set_index(1);
> > +			trace_probe_log_err(0, NO_TRACEPOINT);
> > +			goto parse_error;
> > +		}
> > +		ctx.funcname = kallsyms_lookup(
> > +				(unsigned long)tpoint->probestub,
> > +				NULL, NULL, NULL, sbuf);
> > +	} else
> > +		ctx.funcname = symbol;
> > +
> >  	/* setup a probe */
> > -	tf = alloc_trace_fprobe(group, event, symbol, maxactive,
> > +	tf = alloc_trace_fprobe(group, event, symbol, tpoint, maxactive,
> >  				argc - 2, is_return);
> >  	if (IS_ERR(tf)) {
> >  		ret = PTR_ERR(tf);
> > @@ -1029,24 +1047,15 @@ static int __trace_fprobe_create(int argc, const char *argv[])
> >  		goto out;	/* We know tf is not allocated */
> >  	}
> >  
> > -	if (is_tracepoint) {
> > -		tf->tpoint = find_tracepoint(tf->symbol);
> > -		if (!tf->tpoint) {
> > -			trace_probe_log_set_index(1);
> > -			trace_probe_log_err(0, NO_TRACEPOINT);
> > -			goto parse_error;
> > -		}
> > +	if (is_tracepoint)
> >  		tf->mod = __module_text_address(
> >  				(unsigned long)tf->tpoint->probestub);
> > -	}
> >  
> >  	argc -= 2; argv += 2;
> > -
> >  	/* parse arguments */
> >  	for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
> > -		struct traceprobe_parse_context ctx = { .flags = flags };
> > -
> >  		trace_probe_log_set_index(i + 2);
> > +		ctx.offset = 0;
> >  		ret = traceprobe_parse_probe_arg(&tf->tp, i, argv[i], &ctx);
> >  		if (ret)
> >  			goto error;	/* This can be -ENOMEM */
> > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> > index fd62de2a2f51..aff6c1a5e161 100644
> > --- a/kernel/trace/trace_kprobe.c
> > +++ b/kernel/trace/trace_kprobe.c
> > @@ -742,7 +742,7 @@ static int __trace_kprobe_create(int argc, const char *argv[])
> >  	void *addr = NULL;
> >  	char buf[MAX_EVENT_NAME_LEN];
> >  	char gbuf[MAX_EVENT_NAME_LEN];
> > -	unsigned int flags = TPARG_FL_KERNEL;
> > +	struct traceprobe_parse_context ctx = { .flags = TPARG_FL_KERNEL };
> >  
> >  	switch (argv[0][0]) {
> >  	case 'r':
> > @@ -823,10 +823,10 @@ static int __trace_kprobe_create(int argc, const char *argv[])
> >  			goto parse_error;
> >  		}
> >  		if (is_return)
> > -			flags |= TPARG_FL_RETURN;
> > +			ctx.flags |= TPARG_FL_RETURN;
> >  		ret = kprobe_on_func_entry(NULL, symbol, offset);
> >  		if (ret == 0)
> > -			flags |= TPARG_FL_FENTRY;
> > +			ctx.flags |= TPARG_FL_FENTRY;
> >  		/* Defer the ENOENT case until register kprobe */
> >  		if (ret == -EINVAL && is_return) {
> >  			trace_probe_log_err(0, BAD_RETPROBE);
> > @@ -856,7 +856,7 @@ static int __trace_kprobe_create(int argc, const char *argv[])
> >  
> >  	/* setup a probe */
> >  	tk = alloc_trace_kprobe(group, event, addr, symbol, offset, maxactive,
> > -			       argc - 2, is_return);
> > +				argc - 2, is_return);
> >  	if (IS_ERR(tk)) {
> >  		ret = PTR_ERR(tk);
> >  		/* This must return -ENOMEM, else there is a bug */
> > @@ -866,10 +866,10 @@ static int __trace_kprobe_create(int argc, const char *argv[])
> >  	argc -= 2; argv += 2;
> >  
> >  	/* parse arguments */
> > +	ctx.funcname = symbol;
> >  	for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
> > -		struct traceprobe_parse_context ctx = { .flags = flags };
> > -
> >  		trace_probe_log_set_index(i + 2);
> > +		ctx.offset = 0;
> >  		ret = traceprobe_parse_probe_arg(&tk->tp, i, argv[i], &ctx);
> >  		if (ret)
> >  			goto error;	/* This can be -ENOMEM */
> > diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> > index 84a9f0446390..de30b6add9af 100644
> > --- a/kernel/trace/trace_probe.c
> > +++ b/kernel/trace/trace_probe.c
> > @@ -11,6 +11,8 @@
> >   */
> >  #define pr_fmt(fmt)	"trace_probe: " fmt
> >  
> > +#include <linux/bpf.h>
> > +
> >  #include "trace_probe.h"
> >  
> >  #undef C
> > @@ -300,6 +302,164 @@ static int parse_trace_event_arg(char *arg, struct fetch_insn *code,
> >  	return -ENOENT;
> >  }
> >  
> > +#ifdef CONFIG_PROBE_EVENTS_BTF_ARGS
> > +
> > +static struct btf *traceprobe_get_btf(void)
> > +{
> > +	return bpf_get_btf_vmlinux();
> > +}
> > +
> > +static u32 btf_type_int(const struct btf_type *t)
> > +{
> > +	return *(u32 *)(t + 1);
> > +}
> > +
> > +static const char *type_from_btf_id(struct btf *btf, s32 id)
> > +{
> > +	const struct btf_type *t;
> > +	u32 intdata;
> > +	s32 tid;
> > +
> > +	/* TODO: const char * could be converted as a string */
> > +	t = btf_type_skip_modifiers(btf, id, &tid);
> > +
> > +	switch (BTF_INFO_KIND(t->info)) {
> > +	case BTF_KIND_ENUM:
> > +		/* enum is "int", so convert to "s32" */
> > +		return "s32";
> 
> you could add
> 	case BTF_KIND_ENUM64:
> 		return "s64";
> 
> ...too I guess.

OK, I'll add it too.

> 
> > +	case BTF_KIND_PTR:
> > +		/* pointer will be converted to "x??" */
> > +		if (IS_ENABLED(CONFIG_64BIT))
> > +			return "x64";
> > +		else
> > +			return "x32";
> > +	case BTF_KIND_INT:
> > +		intdata = btf_type_int(t);
> > +		if (BTF_INT_ENCODING(intdata) & BTF_INT_SIGNED) {
> > +			switch (BTF_INT_BITS(intdata)) {
> > +			case 8:
> > +				return "s8";
> > +			case 16:
> > +				return "s16";
> > +			case 32:
> > +				return "s32";
> > +			case 64:
> > +				return "s64";
> > +			}
> > +		} else {	/* unsigned */
> > +			switch (BTF_INT_BITS(intdata)) {
> > +			case 8:
> > +				return "u8";
> > +			case 16:
> > +				return "u16";
> > +			case 32:
> > +				return "u32";
> > +			case 64:
> > +				return "u64";
> > +			}
> > +		}
> > +	}
> > +	/* TODO: support other types */
> > +
> > +	return NULL;
> > +}
> > +
> > +static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr)
> > +{
> > +	struct btf *btf = traceprobe_get_btf();
> > +	const struct btf_type *t;
> > +	s32 id;
> > +
> > +	if (!btf || !funcname || !nr)
> 
> I _think_ you need IS_ERR_OR_NULL(btf) handling for the struct btf * here; 
> btf_parse_vmlinux() mostly returns ERR_PTR values, while btf_vmlinux
> can be NULL if BTF isn't present.

Ah, I missed that. To simplify the code, I will handle that in traceprobe_get_btf().

Thank you!

>  
> > +		return ERR_PTR(-EINVAL);
> > +
> > +	id = btf_find_by_name_kind(btf, funcname, BTF_KIND_FUNC);
> > +	if (id <= 0)
> > +		return ERR_PTR(-ENOENT);
> > +
> > +	/* Get BTF_KIND_FUNC type */
> > +	t = btf_type_by_id(btf, id);
> > +	if (!btf_type_is_func(t))
> > +		return ERR_PTR(-ENOENT);
> > +
> > +	/* The type of BTF_KIND_FUNC is BTF_KIND_FUNC_PROTO */
> > +	t = btf_type_by_id(btf, t->type);
> > +	if (!btf_type_is_func_proto(t))
> > +		return ERR_PTR(-ENOENT);
> > +
> > +	*nr = btf_type_vlen(t);
> > +
> > +	if (*nr)
> > +		return (const struct btf_param *)(t + 1);
> > +	else
> > +		return NULL;
> > +}
> > +
> > +static int parse_btf_arg(const char *varname, struct fetch_insn *code,
> > +			 struct traceprobe_parse_context *ctx)
> > +{
> > +	struct btf *btf = traceprobe_get_btf();
> > +	const struct btf_param *params;
> > +	int i;
> > +
> > +	if (!btf) {
> > +		trace_probe_log_err(ctx->offset, NOSUP_BTFARG);
> > +		return -EOPNOTSUPP;
> > +	}
> > +
> > +	if (WARN_ON_ONCE(!ctx->funcname))
> > +		return -EINVAL;
> > +
> > +	if (!ctx->params) {
> > +		params = find_btf_func_param(ctx->funcname, &ctx->nr_params);
> > +		if (IS_ERR(params)) {
> > +			trace_probe_log_err(ctx->offset, NO_BTF_ENTRY);
> > +			return PTR_ERR(params);
> > +		}
> > +		ctx->params = params;
> > +	} else
> > +		params = ctx->params;
> > +
> > +	for (i = 0; i < ctx->nr_params; i++) {
> > +		const char *name = btf_name_by_offset(btf, params[i].name_off);
> > +
> > +		if (name && !strcmp(name, varname)) {
> > +			code->op = FETCH_OP_ARG;
> > +			code->param = i;
> > +			return 0;
> > +		}
> > +	}
> > +	trace_probe_log_err(ctx->offset, NO_BTFARG);
> > +	return -ENOENT;
> > +}
> > +
> > +static const struct fetch_type *parse_btf_arg_type(int arg_idx,
> > +					struct traceprobe_parse_context *ctx)
> > +{
> > +	struct btf *btf = traceprobe_get_btf();
> > +	const char *typestr = NULL;
> > +
> > +	if (btf && ctx->params)
> > +		typestr = type_from_btf_id(btf, ctx->params[arg_idx].type);
> > +
> > +	return find_fetch_type(typestr, ctx->flags);
> > +}
> > +#else
> > +static struct btf *traceprobe_get_btf(void)
> > +{
> > +	return NULL;
> > +}
> > +
> > +static int parse_btf_arg(const char *varname, struct fetch_insn *code,
> > +			 struct traceprobe_parse_context *ctx)
> > +{
> > +	trace_probe_log_err(ctx->offset, NOSUP_BTFARG);
> > +	return -EOPNOTSUPP;
> > +}
> > +#define parse_btf_arg_type(idx, ctx)		\
> > +	find_fetch_type(NULL, ctx->flags)
> > +#endif
> > +
> >  #define PARAM_MAX_STACK (THREAD_SIZE / sizeof(unsigned long))
> >  
> >  static int parse_probe_vars(char *arg, const struct fetch_type *t,
> > @@ -556,6 +716,15 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
> >  				code->op = FETCH_OP_IMM;
> >  		}
> >  		break;
> > +	default:
> > +		if (isalpha(arg[0]) || arg[0] == '_') {	/* BTF variable */
> > +			if (!tparg_is_function_entry(ctx->flags)) {
> > +				trace_probe_log_err(ctx->offset, NOSUP_BTFARG);
> > +				return -EINVAL;
> > +			}
> > +			ret = parse_btf_arg(arg, code, ctx);
> > +			break;
> > +		}
> >  	}
> >  	if (!ret && code->op == FETCH_OP_NOP) {
> >  		/* Parsed, but do not find fetch method */
> > @@ -704,6 +873,11 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
> >  	if (ret)
> >  		goto fail;
> >  
> > +	/* Update storing type if BTF is available */
> > +	if (IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS) &&
> > +	    !t && code->op == FETCH_OP_ARG)
> > +		parg->type = parse_btf_arg_type(code->param, ctx);
> > +
> >  	ret = -EINVAL;
> >  	/* Store operation */
> >  	if (parg->type->is_string) {
> > @@ -857,8 +1031,14 @@ int traceprobe_parse_probe_arg(struct trace_probe *tp, int i, const char *arg,
> >  		parg->name = kmemdup_nul(arg, body - arg, GFP_KERNEL);
> >  		body++;
> >  	} else {
> > -		/* If argument name is omitted, set "argN" */
> > -		parg->name = kasprintf(GFP_KERNEL, "arg%d", i + 1);
> > +		/*
> > +		 * If argument name is omitted, try arg as a name (BTF variable)
> > +		 * or "argN".
> > +		 */
> > +		if (is_good_name(arg))
> > +			parg->name = kstrdup(arg, GFP_KERNEL);
> > +		else
> > +			parg->name = kasprintf(GFP_KERNEL, "arg%d", i + 1);
> >  		body = arg;
> >  	}
> >  	if (!parg->name)
> > diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
> > index 2dc1e5c4c9e8..9ea5c7e8753f 100644
> > --- a/kernel/trace/trace_probe.h
> > +++ b/kernel/trace/trace_probe.h
> > @@ -23,6 +23,7 @@
> >  #include <linux/limits.h>
> >  #include <linux/uaccess.h>
> >  #include <linux/bitops.h>
> > +#include <linux/btf.h>
> >  #include <asm/bitsperlong.h>
> >  
> >  #include "trace.h"
> > @@ -376,6 +377,9 @@ static inline bool tparg_is_function_entry(unsigned int flags)
> >  
> >  struct traceprobe_parse_context {
> >  	struct trace_event_call *event;
> > +	const struct btf_param *params;
> > +	s32 nr_params;
> > +	const char *funcname;
> >  	unsigned int flags;
> >  	int offset;
> >  };
> > @@ -474,7 +478,10 @@ extern int traceprobe_define_arg_fields(struct trace_event_call *event_call,
> >  	C(NO_EVENT_INFO,	"This requires both group and event name to attach"),\
> >  	C(BAD_ATTACH_EVENT,	"Attached event does not exist"),\
> >  	C(BAD_ATTACH_ARG,	"Attached event does not have this field"),\
> > -	C(NO_EP_FILTER,		"No filter rule after 'if'"),
> > +	C(NO_EP_FILTER,		"No filter rule after 'if'"),		\
> > +	C(NOSUP_BTFARG,		"BTF is not available or not supported"),	\
> > +	C(NO_BTFARG,		"This variable is not found at this probe point"),\
> > +	C(NO_BTF_ENTRY,		"No BTF entry for this probe point"),
> >  
> >  #undef C
> >  #define C(a, b)		TP_ERR_##a
> > 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>

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