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tracing/probes: Support BTF based data structure field access 

Using BTF to access the fields of a data structure. You can use this
for accessing the field with '->' or '.' operation with BTF argument.

 # echo 't sched_switch next=next->pid vruntime=next->se.vruntime' \
   > dynamic_events
 # echo 1 > events/tracepoints/sched_switch/enable
 # head -n 40 trace | tail
          <idle>-0       [000] d..3.   272.565382: sched_switch: (__probestub_sched_switch+0x4/0x10) next=26 vruntime=956533179
      kcompactd0-26      [000] d..3.   272.565406: sched_switch: (__probestub_sched_switch+0x4/0x10) next=0 vruntime=0
          <idle>-0       [000] d..3.   273.069441: sched_switch: (__probestub_sched_switch+0x4/0x10) next=9 vruntime=956533179
     kworker/0:1-9       [000] d..3.   273.069464: sched_switch: (__probestub_sched_switch+0x4/0x10) next=26 vruntime=956579181
      kcompactd0-26      [000] d..3.   273.069480: sched_switch: (__probestub_sched_switch+0x4/0x10) next=0 vruntime=0
          <idle>-0       [000] d..3.   273.141434: sched_switch: (__probestub_sched_switch+0x4/0x10) next=22 vruntime=956533179
    kworker/u2:1-22      [000] d..3.   273.141461: sched_switch: (__probestub_sched_switch+0x4/0x10) next=0 vruntime=0
          <idle>-0       [000] d..3.   273.480872: sched_switch: (__probestub_sched_switch+0x4/0x10) next=22 vruntime=956585857
    kworker/u2:1-22      [000] d..3.   273.480905: sched_switch: (__probestub_sched_switch+0x4/0x10) next=70 vruntime=959533179
              sh-70      [000] d..3.   273.481102: sched_switch: (__probestub_sched_switch+0x4/0x10) next=0 vruntime=0

Link: https://lore.kernel.org/all/169272157251.160970.9318175874130965571.stgit@devnote2/

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Masami Hiramatsu (Google) 2023-08-23 01:26:12 +09:00
parent 302db0f5b3
commit c440adfbe3
3 changed files with 216 additions and 28 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
kernel/trace/trace.c
View File

@ -5717,7 +5717,8 @@ static const char readme_msg[] =
"\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"
"\t $stack<index>, $stack, $retval, $comm, $arg<N>,\n"
"\t <argname>[->field[->field|.field...]],\n"
#else
"\t $stack<index>, $stack, $retval, $comm, $arg<N>,\n"
#endif

230
kernel/trace/trace_probe.c
View File

@ -310,16 +310,14 @@ 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)
static const char *fetch_type_from_btf_type(struct btf *btf,
const struct btf_type *type,
struct traceprobe_parse_context *ctx)
{
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)) {
switch (BTF_INFO_KIND(type->info)) {
case BTF_KIND_ENUM:
/* enum is "int", so convert to "s32" */
return "s32";
@ -332,7 +330,7 @@ static const char *type_from_btf_id(struct btf *btf, s32 id)
else
return "x32";
case BTF_KIND_INT:
intdata = btf_type_int(t);
intdata = btf_type_int(type);
if (BTF_INT_ENCODING(intdata) & BTF_INT_SIGNED) {
switch (BTF_INT_BITS(intdata)) {
case 8:
@ -355,6 +353,10 @@ static const char *type_from_btf_id(struct btf *btf, s32 id)
case 64:
return "u64";
}
/* bitfield, size is encoded in the type */
ctx->last_bitsize = BTF_INT_BITS(intdata);
ctx->last_bitoffs += BTF_INT_OFFSET(intdata);
return "u64";
}
}
/* TODO: support other types */
@ -406,15 +408,136 @@ static void clear_btf_context(struct traceprobe_parse_context *ctx)
}
}
static int parse_btf_arg(const char *varname, struct fetch_insn *code,
/* Return 1 if the field separater is arrow operator ('->') */
static int split_next_field(char *varname, char **next_field,
struct traceprobe_parse_context *ctx)
{
char *field;
int ret = 0;
field = strpbrk(varname, ".-");
if (field) {
if (field[0] == '-' && field[1] == '>') {
field[0] = '\0';
field += 2;
ret = 1;
} else if (field[0] == '.') {
field[0] = '\0';
field += 1;
} else {
trace_probe_log_err(ctx->offset + field - varname, BAD_HYPHEN);
return -EINVAL;
}
*next_field = field;
}
return ret;
}
/*
* Parse the field of data structure. The @type must be a pointer type
* pointing the target data structure type.
*/
static int parse_btf_field(char *fieldname, const struct btf_type *type,
struct fetch_insn **pcode, struct fetch_insn *end,
struct traceprobe_parse_context *ctx)
{
struct fetch_insn *code = *pcode;
const struct btf_member *field;
u32 bitoffs, anon_offs;
char *next;
int is_ptr;
s32 tid;
do {
/* Outer loop for solving arrow operator ('->') */
if (BTF_INFO_KIND(type->info) != BTF_KIND_PTR) {
trace_probe_log_err(ctx->offset, NO_PTR_STRCT);
return -EINVAL;
}
/* Convert a struct pointer type to a struct type */
type = btf_type_skip_modifiers(ctx->btf, type->type, &tid);
if (!type) {
trace_probe_log_err(ctx->offset, BAD_BTF_TID);
return -EINVAL;
}
bitoffs = 0;
do {
/* Inner loop for solving dot operator ('.') */
next = NULL;
is_ptr = split_next_field(fieldname, &next, ctx);
if (is_ptr < 0)
return is_ptr;
anon_offs = 0;
field = btf_find_struct_member(ctx->btf, type, fieldname,
&anon_offs);
if (!field) {
trace_probe_log_err(ctx->offset, NO_BTF_FIELD);
return -ENOENT;
}
/* Add anonymous structure/union offset */
bitoffs += anon_offs;
/* Accumulate the bit-offsets of the dot-connected fields */
if (btf_type_kflag(type)) {
bitoffs += BTF_MEMBER_BIT_OFFSET(field->offset);
ctx->last_bitsize = BTF_MEMBER_BITFIELD_SIZE(field->offset);
} else {
bitoffs += field->offset;
ctx->last_bitsize = 0;
}
type = btf_type_skip_modifiers(ctx->btf, field->type, &tid);
if (!type) {
trace_probe_log_err(ctx->offset, BAD_BTF_TID);
return -EINVAL;
}
ctx->offset += next - fieldname;
fieldname = next;
} while (!is_ptr && fieldname);
if (++code == end) {
trace_probe_log_err(ctx->offset, TOO_MANY_OPS);
return -EINVAL;
}
code->op = FETCH_OP_DEREF; /* TODO: user deref support */
code->offset = bitoffs / 8;
*pcode = code;
ctx->last_bitoffs = bitoffs % 8;
ctx->last_type = type;
} while (fieldname);
return 0;
}
static int parse_btf_arg(char *varname,
struct fetch_insn **pcode, struct fetch_insn *end,
struct traceprobe_parse_context *ctx)
{
struct fetch_insn *code = *pcode;
const struct btf_param *params;
int i;
const struct btf_type *type;
char *field = NULL;
int i, is_ptr;
u32 tid;
if (WARN_ON_ONCE(!ctx->funcname))
return -EINVAL;
is_ptr = split_next_field(varname, &field, ctx);
if (is_ptr < 0)
return is_ptr;
if (!is_ptr && field) {
/* dot-connected field on an argument is not supported. */
trace_probe_log_err(ctx->offset + field - varname,
NOSUP_DAT_ARG);
return -EOPNOTSUPP;
}
if (!ctx->params) {
params = find_btf_func_param(ctx->funcname,
&ctx->nr_params, &ctx->btf,
@ -436,24 +559,39 @@ static int parse_btf_arg(const char *varname, struct fetch_insn *code,
code->param = i + 1;
else
code->param = i;
return 0;
tid = params[i].type;
goto found;
}
}
trace_probe_log_err(ctx->offset, NO_BTFARG);
return -ENOENT;
found:
type = btf_type_skip_modifiers(ctx->btf, tid, &tid);
if (!type) {
trace_probe_log_err(ctx->offset, BAD_BTF_TID);
return -EINVAL;
}
/* Initialize the last type information */
ctx->last_type = type;
ctx->last_bitoffs = 0;
ctx->last_bitsize = 0;
if (field) {
ctx->offset += field - varname;
return parse_btf_field(field, type, pcode, end, ctx);
}
return 0;
}
static const struct fetch_type *parse_btf_arg_type(int arg_idx,
static const struct fetch_type *parse_btf_arg_type(
struct traceprobe_parse_context *ctx)
{
struct btf *btf = ctx->btf;
const char *typestr = NULL;
if (btf && ctx->params) {
if (ctx->flags & TPARG_FL_TPOINT)
arg_idx--;
typestr = type_from_btf_id(btf, ctx->params[arg_idx].type);
}
if (btf && ctx->last_type)
typestr = fetch_type_from_btf_type(btf, ctx->last_type, ctx);
return find_fetch_type(typestr, ctx->flags);
}
@ -462,14 +600,16 @@ static const struct fetch_type *parse_btf_retval_type(
struct traceprobe_parse_context *ctx)
{
const char *typestr = NULL;
const struct btf_type *t;
const struct btf_type *type;
struct btf *btf;
if (ctx->funcname) {
/* Do not use ctx->btf, because it must be used with ctx->param */
t = btf_find_func_proto(ctx->funcname, &btf);
if (t) {
typestr = type_from_btf_id(btf, t->type);
type = btf_find_func_proto(ctx->funcname, &btf);
if (type) {
type = btf_type_skip_modifiers(btf, type->type, NULL);
if (!IS_ERR_OR_NULL(type))
typestr = fetch_type_from_btf_type(btf, type, ctx);
btf_put(btf);
}
}
@ -477,6 +617,28 @@ static const struct fetch_type *parse_btf_retval_type(
return find_fetch_type(typestr, ctx->flags);
}
static int parse_btf_bitfield(struct fetch_insn **pcode,
struct traceprobe_parse_context *ctx)
{
struct fetch_insn *code = *pcode;
if ((ctx->last_bitsize % 8 == 0) && ctx->last_bitoffs == 0)
return 0;
code++;
if (code->op != FETCH_OP_NOP) {
trace_probe_log_err(ctx->offset, TOO_MANY_OPS);
return -EINVAL;
}
*pcode = code;
code->op = FETCH_OP_MOD_BF;
code->lshift = 64 - (ctx->last_bitsize + ctx->last_bitoffs);
code->rshift = 64 - ctx->last_bitsize;
code->basesize = 64 / 8;
return 0;
}
static bool is_btf_retval_void(const char *funcname)
{
const struct btf_type *t;
@ -503,14 +665,22 @@ static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr
return ERR_PTR(-EOPNOTSUPP);
}
static int parse_btf_arg(const char *varname, struct fetch_insn *code,
static int parse_btf_arg(char *varname,
struct fetch_insn **pcode, struct fetch_insn *end,
struct traceprobe_parse_context *ctx)
{
trace_probe_log_err(ctx->offset, NOSUP_BTFARG);
return -EOPNOTSUPP;
}
#define parse_btf_arg_type(idx, ctx) \
static int parse_btf_bitfield(struct fetch_insn **pcode,
struct traceprobe_parse_context *ctx)
{
trace_probe_log_err(ctx->offset, NOSUP_BTFARG);
return -EOPNOTSUPP;
}
#define parse_btf_arg_type(ctx) \
find_fetch_type(NULL, ctx->flags)
#define parse_btf_retval_type(ctx) \
@ -778,6 +948,8 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
code->op = deref;
code->offset = offset;
/* Reset the last type if used */
ctx->last_type = NULL;
}
break;
case '\\': /* Immediate value */
@ -801,7 +973,7 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
trace_probe_log_err(ctx->offset, NOSUP_BTFARG);
return -EINVAL;
}
ret = parse_btf_arg(arg, code, ctx);
ret = parse_btf_arg(arg, pcode, end, ctx);
break;
}
}
@ -947,6 +1119,7 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
goto out;
code[FETCH_INSN_MAX - 1].op = FETCH_OP_END;
ctx->last_type = NULL;
ret = parse_probe_arg(arg, parg->type, &code, &code[FETCH_INSN_MAX - 1],
ctx);
if (ret)
@ -954,9 +1127,9 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
/* Update storing type if BTF is available */
if (IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS) && !t) {
if (code->op == FETCH_OP_ARG)
parg->type = parse_btf_arg_type(code->param, ctx);
else if (code->op == FETCH_OP_RETVAL)
if (ctx->last_type)
parg->type = parse_btf_arg_type(ctx);
else if (ctx->flags & TPARG_FL_RETURN)
parg->type = parse_btf_retval_type(ctx);
}
@ -1031,6 +1204,11 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
trace_probe_log_err(ctx->offset + t - arg, BAD_BITFIELD);
goto fail;
}
} else if (IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS) &&
ctx->last_type) {
ret = parse_btf_bitfield(&code, ctx);
if (ret)
goto fail;
}
ret = -EINVAL;
/* Loop(Array) operation */

11
kernel/trace/trace_probe.h
View File

@ -388,6 +388,9 @@ struct traceprobe_parse_context {
const struct btf_param *params; /* Parameter of the function */
s32 nr_params; /* The number of the parameters */
struct btf *btf; /* The BTF to be used */
const struct btf_type *last_type; /* Saved type */
u32 last_bitoffs; /* Saved bitoffs */
u32 last_bitsize; /* Saved bitsize */
unsigned int flags;
int offset;
};
@ -503,7 +506,13 @@ extern int traceprobe_define_arg_fields(struct trace_event_call *event_call,
C(BAD_VAR_ARGS, "$arg* must be an independent parameter without name etc."),\
C(NOFENTRY_ARGS, "$arg* can be used only on function entry"), \
C(DOUBLE_ARGS, "$arg* can be used only once in the parameters"), \
C(ARGS_2LONG, "$arg* failed because the argument list is too long"),
C(ARGS_2LONG, "$arg* failed because the argument list is too long"), \
C(ARGIDX_2BIG, "$argN index is too big"), \
C(NO_PTR_STRCT, "This is not a pointer to union/structure."), \
C(NOSUP_DAT_ARG, "Non pointer structure/union argument is not supported."),\
C(BAD_HYPHEN, "Failed to parse single hyphen. Forgot '>'?"), \
C(NO_BTF_FIELD, "This field is not found."), \
C(BAD_BTF_TID, "Failed to get BTF type info."),
#undef C
#define C(a, b) TP_ERR_##a