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libbpf: Refactor and simplify legacy kprobe code 

Refactor legacy kprobe handling code to follow the same logic as uprobe
legacy logic added in the next patchs:
  - add append_to_file() helper that makes it simpler to work with
    tracefs file-based interface for creating and deleting probes;
  - move out probe/event name generation outside of the code that
    adds/removes it, which simplifies bookkeeping significantly;
  - change the probe name format to start with "libbpf_" prefix and
    include offset within kernel function;
  - switch 'unsigned long' to 'size_t' for specifying kprobe offsets,
    which is consistent with how uprobes define that, simplifies
    printf()-ing internally, and also avoids unnecessary complications on
    architectures where sizeof(long) != sizeof(void *).

This patch also implicitly fixes the problem with invalid open() error
handling present in poke_kprobe_events(), which (the function) this
patch removes.

Fixes: ca304b40c2 ("libbpf: Introduce legacy kprobe events support")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210921210036.1545557-4-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko 2021-09-21 14:00:35 -07:00 committed by Alexei Starovoitov
parent d3b0e3b03c
commit 46ed5fc33d
2 changed files with 88 additions and 73 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

159
tools/lib/bpf/libbpf.c
View File

@ -9011,59 +9011,17 @@ int bpf_link__unpin(struct bpf_link *link)
return 0;
}
static int poke_kprobe_events(bool add, const char *name, bool retprobe, uint64_t offset)
{
int fd, ret = 0;
pid_t p = getpid();
char cmd[260], probename[128], probefunc[128];
const char *file = "/sys/kernel/debug/tracing/kprobe_events";
if (retprobe)
snprintf(probename, sizeof(probename), "kretprobes/%s_libbpf_%u", name, p);
else
snprintf(probename, sizeof(probename), "kprobes/%s_libbpf_%u", name, p);
if (offset)
snprintf(probefunc, sizeof(probefunc), "%s+%zu", name, (size_t)offset);
if (add) {
snprintf(cmd, sizeof(cmd), "%c:%s %s",
retprobe ? 'r' : 'p',
probename,
offset ? probefunc : name);
} else {
snprintf(cmd, sizeof(cmd), "-:%s", probename);
}
fd = open(file, O_WRONLY | O_APPEND, 0);
if (!fd)
return -errno;
ret = write(fd, cmd, strlen(cmd));
if (ret < 0)
ret = -errno;
close(fd);
return ret;
}
static inline int add_kprobe_event_legacy(const char *name, bool retprobe, uint64_t offset)
{
return poke_kprobe_events(true, name, retprobe, offset);
}
static inline int remove_kprobe_event_legacy(const char *name, bool retprobe)
{
return poke_kprobe_events(false, name, retprobe, 0);
}
struct bpf_link_perf {
struct bpf_link link;
int perf_event_fd;
/* legacy kprobe support: keep track of probe identifier and type */
char *legacy_probe_name;
bool legacy_is_kprobe;
bool legacy_is_retprobe;
};
static int remove_kprobe_event_legacy(const char *probe_name, bool retprobe);
static int bpf_link_perf_detach(struct bpf_link *link)
{
struct bpf_link_perf *perf_link = container_of(link, struct bpf_link_perf, link);
@ -9077,9 +9035,12 @@ static int bpf_link_perf_detach(struct bpf_link *link)
close(link->fd);
/* legacy kprobe needs to be removed after perf event fd closure */
if (perf_link->legacy_probe_name)
err = remove_kprobe_event_legacy(perf_link->legacy_probe_name,
perf_link->legacy_is_retprobe);
if (perf_link->legacy_probe_name) {
if (perf_link->legacy_is_kprobe) {
err = remove_kprobe_event_legacy(perf_link->legacy_probe_name,
perf_link->legacy_is_retprobe);
}
}
return err;
}
@ -9202,18 +9163,6 @@ static int parse_uint_from_file(const char *file, const char *fmt)
return ret;
}
static int determine_kprobe_perf_type_legacy(const char *func_name, bool is_retprobe)
{
char file[192];
snprintf(file, sizeof(file),
"/sys/kernel/debug/tracing/events/%s/%s_libbpf_%d/id",
is_retprobe ? "kretprobes" : "kprobes",
func_name, getpid());
return parse_uint_from_file(file, "%d\n");
}
static int determine_kprobe_perf_type(void)
{
const char *file = "/sys/bus/event_source/devices/kprobe/type";
@ -9296,21 +9245,79 @@ static int perf_event_open_probe(bool uprobe, bool retprobe, const char *name,
return pfd;
}
static int perf_event_kprobe_open_legacy(bool retprobe, const char *name, uint64_t offset, int pid)
static int append_to_file(const char *file, const char *fmt, ...)
{
int fd, n, err = 0;
va_list ap;
fd = open(file, O_WRONLY | O_APPEND, 0);
if (fd < 0)
return -errno;
va_start(ap, fmt);
n = vdprintf(fd, fmt, ap);
va_end(ap);
if (n < 0)
err = -errno;
close(fd);
return err;
}
static void gen_kprobe_legacy_event_name(char *buf, size_t buf_sz,
const char *kfunc_name, size_t offset)
{
snprintf(buf, buf_sz, "libbpf_%u_%s_0x%zx", getpid(), kfunc_name, offset);
}
static int add_kprobe_event_legacy(const char *probe_name, bool retprobe,
const char *kfunc_name, size_t offset)
{
const char *file = "/sys/kernel/debug/tracing/kprobe_events";
return append_to_file(file, "%c:%s/%s %s+0x%zx",
retprobe ? 'r' : 'p',
retprobe ? "kretprobes" : "kprobes",
probe_name, kfunc_name, offset);
}
static int remove_kprobe_event_legacy(const char *probe_name, bool retprobe)
{
const char *file = "/sys/kernel/debug/tracing/kprobe_events";
return append_to_file(file, "-:%s/%s", retprobe ? "kretprobes" : "kprobes", probe_name);
}
static int determine_kprobe_perf_type_legacy(const char *probe_name, bool retprobe)
{
char file[256];
snprintf(file, sizeof(file),
"/sys/kernel/debug/tracing/events/%s/%s/id",
retprobe ? "kretprobes" : "kprobes", probe_name);
return parse_uint_from_file(file, "%d\n");
}
static int perf_event_kprobe_open_legacy(const char *probe_name, bool retprobe,
const char *kfunc_name, size_t offset, int pid)
{
struct perf_event_attr attr = {};
char errmsg[STRERR_BUFSIZE];
int type, pfd, err;
err = add_kprobe_event_legacy(name, retprobe, offset);
err = add_kprobe_event_legacy(probe_name, retprobe, kfunc_name, offset);
if (err < 0) {
pr_warn("failed to add legacy kprobe event: %s\n",
pr_warn("failed to add legacy kprobe event for '%s+0x%zx': %s\n",
kfunc_name, offset,
libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
return err;
}
type = determine_kprobe_perf_type_legacy(name, retprobe);
type = determine_kprobe_perf_type_legacy(probe_name, retprobe);
if (type < 0) {
pr_warn("failed to determine legacy kprobe event id: %s\n",
pr_warn("failed to determine legacy kprobe event id for '%s+0x%zx': %s\n",
kfunc_name, offset,
libbpf_strerror_r(type, errmsg, sizeof(errmsg)));
return type;
}
@ -9340,7 +9347,7 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
char errmsg[STRERR_BUFSIZE];
char *legacy_probe = NULL;
struct bpf_link *link;
unsigned long offset;
size_t offset;
bool retprobe, legacy;
int pfd, err;
@ -9357,17 +9364,23 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
func_name, offset,
-1 /* pid */, 0 /* ref_ctr_off */);
} else {
char probe_name[256];
gen_kprobe_legacy_event_name(probe_name, sizeof(probe_name),
func_name, offset);
legacy_probe = strdup(func_name);
if (!legacy_probe)
return libbpf_err_ptr(-ENOMEM);
pfd = perf_event_kprobe_open_legacy(retprobe, func_name,
pfd = perf_event_kprobe_open_legacy(legacy_probe, retprobe, func_name,
offset, -1 /* pid */);
}
if (pfd < 0) {
err = pfd;
pr_warn("prog '%s': failed to create %s '%s' perf event: %s\n",
prog->name, retprobe ? "kretprobe" : "kprobe", func_name,
err = -errno;
pr_warn("prog '%s': failed to create %s '%s+0x%zx' perf event: %s\n",
prog->name, retprobe ? "kretprobe" : "kprobe",
func_name, offset,
libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
goto err_out;
}
@ -9375,8 +9388,9 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
err = libbpf_get_error(link);
if (err) {
close(pfd);
pr_warn("prog '%s': failed to attach to %s '%s': %s\n",
prog->name, retprobe ? "kretprobe" : "kprobe", func_name,
pr_warn("prog '%s': failed to attach to %s '%s+0x%zx': %s\n",
prog->name, retprobe ? "kretprobe" : "kprobe",
func_name, offset,
libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
goto err_out;
}
@ -9384,6 +9398,7 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
struct bpf_link_perf *perf_link = container_of(link, struct bpf_link_perf, link);
perf_link->legacy_probe_name = legacy_probe;
perf_link->legacy_is_kprobe = true;
perf_link->legacy_is_retprobe = retprobe;
}

2
tools/lib/bpf/libbpf.h
View File

@ -269,7 +269,7 @@ struct bpf_kprobe_opts {
/* custom user-provided value fetchable through bpf_get_attach_cookie() */
__u64 bpf_cookie;
/* function's offset to install kprobe to */
unsigned long offset;
size_t offset;
/* kprobe is return probe */
bool retprobe;
size_t :0;