On 07/12, Andrii Nakryiko wrote:
Libbpf supports single virtual __kconfig extern currently:
LINUX_KERNEL_VERSION.
LINUX_KERNEL_VERSION isn't coming from /proc/kconfig.gz and is intead
customly filled out by libbpf.
This patch generalizes this approach to support more such virtual
__kconfig externs. One such extern added in this patch is
LINUX_HAS_BPF_COOKIE which is used for BPF-side USDT supporting code in
usdt.bpf.h instead of using CO-RE-based enum detection approach for
detecting bpf_get_attach_cookie() BPF helper. This allows to remove
otherwise not needed CO-RE dependency and keeps user-space and BPF-side
parts of libbpf's USDT support strictly in sync in terms of their
feature detection.
We'll use similar approach for syscall wrapper detection for
BPF_KSYSCALL() BPF-side macro in follow up patch.
Generally, currently libbpf reserves CONFIG_ prefix for Kconfig values
and LINUX_ for virtual libbpf-backed externs. In the future we might
extend the set of prefixes that are supported. This can be done without
any breaking changes, as currently any __kconfig extern with
unrecognized name is rejected.
For LINUX_xxx externs we support the normal "weak rule": if libbpf
doesn't recognize given LINUX_xxx extern but such extern is marked as
__weak, it is not rejected and defaults to zero. This follows
CONFIG_xxx handling logic and will allow BPF applications to
opportunistically use newer libbpf virtual externs without breaking on
older libbpf versions unnecessarily.
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
---
tools/lib/bpf/libbpf.c | 69 +++++++++++++++++++++++++++++-----------
tools/lib/bpf/usdt.bpf.h | 16 ++--------
2 files changed, 52 insertions(+), 33 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index cb49408eb298..4bae67767f82 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -1800,11 +1800,18 @@ static bool is_kcfg_value_in_range(const struct
extern_desc *ext, __u64 v)
static int set_kcfg_value_num(struct extern_desc *ext, void *ext_val,
__u64 value)
{
- if (ext->kcfg.type != KCFG_INT && ext->kcfg.type != KCFG_CHAR) {
- pr_warn("extern (kcfg) %s=%llu should be integer\n",
+ if (ext->kcfg.type != KCFG_INT && ext->kcfg.type != KCFG_CHAR &&
+ ext->kcfg.type != KCFG_BOOL) {
+ pr_warn("extern (kcfg) %s=%llu should be integer, char or boolean\n",
ext->name, (unsigned long long)value);
return -EINVAL;
}
+ if (ext->kcfg.type == KCFG_BOOL && value > 1) {
+ pr_warn("extern (kcfg) %s=%llu value isn't boolean\n",
+ ext->name, (unsigned long long)value);
+ return -EINVAL;
+
+ }
if (!is_kcfg_value_in_range(ext, value)) {
pr_warn("extern (kcfg) %s=%llu value doesn't fit in %d bytes\n",
ext->name, (unsigned long long)value, ext->kcfg.sz);
@@ -1870,10 +1877,13 @@ static int
bpf_object__process_kconfig_line(struct bpf_object *obj,
/* assume integer */
err = parse_u64(value, &num);
if (err) {
- pr_warn("extern (kcfg) %s=%s should be integer\n",
- ext->name, value);
+ pr_warn("extern (kcfg) %s=%s should be integer\n", ext->name, value);
return err;
}
+ if (ext->kcfg.type != KCFG_INT && ext->kcfg.type != KCFG_CHAR) {
+ pr_warn("extern (kcfg) %s=%s should be integer\n", ext->name, value);
+ return -EINVAL;
+ }
err = set_kcfg_value_num(ext, ext_val, num);
break;
}
@@ -7493,26 +7503,47 @@ static int bpf_object__resolve_externs(struct
bpf_object *obj,
for (i = 0; i < obj->nr_extern; i++) {
ext = &obj->externs[i];
- if (ext->type == EXT_KCFG &&
- strcmp(ext->name, "LINUX_KERNEL_VERSION") == 0) {
- void *ext_val = kcfg_data + ext->kcfg.data_off;
- __u32 kver = get_kernel_version();
+ if (ext->type == EXT_KSYM) {
+ if (ext->ksym.type_id)
+ need_vmlinux_btf = true;
+ else
+ need_kallsyms = true;
+ continue;
+ } else if (ext->type == EXT_KCFG) {
+ void *ext_ptr = kcfg_data + ext->kcfg.data_off;
+ __u64 value = 0;
+
+ /* Kconfig externs need actual /proc/config.gz */
+ if (str_has_pfx(ext->name, "CONFIG_")) {
+ need_config = true;
+ continue;
+ }
- if (!kver) {
- pr_warn("failed to get kernel version\n");
+ /* Virtual kcfg externs are customly handled by libbpf */
+ if (strcmp(ext->name, "LINUX_KERNEL_VERSION") == 0) {
+ value = get_kernel_version();
+ if (!value) {
+ pr_warn("extern (kcfg) '%s': failed to get kernel version\n",
ext->name);
+ return -EINVAL;
+ }
+ } else if (strcmp(ext->name, "LINUX_HAS_BPF_COOKIE") == 0) {
+ value = kernel_supports(obj, FEAT_BPF_COOKIE);
+ } else if (!str_has_pfx(ext->name, "LINUX_") || !ext->is_weak) {
+ /* Currently libbpf supports only CONFIG_ and LINUX_ prefixed
+ * __kconfig externs, where LINUX_ ones are virtual and filled out
+ * customly by libbpf (their values don't come from Kconfig).
+ * If LINUX_xxx variable is not recognized by libbpf, but is marked
+ * __weak, it defaults to zero value, just like for CONFIG_xxx
+ * externs.
+ */
+ pr_warn("extern (kcfg) '%s': unrecognized virtual extern\n",
ext->name);
return -EINVAL;
}
- err = set_kcfg_value_num(ext, ext_val, kver);
+
+ err = set_kcfg_value_num(ext, ext_ptr, value);
if (err)
return err;
- pr_debug("extern (kcfg) %s=0x%x\n", ext->name, kver);
- } else if (ext->type == EXT_KCFG && str_has_pfx(ext->name, "CONFIG_"))
{
- need_config = true;
- } else if (ext->type == EXT_KSYM) {
- if (ext->ksym.type_id)
- need_vmlinux_btf = true;
- else
- need_kallsyms = true;
+ pr_debug("extern (kcfg) %s=0x%llx\n", ext->name, (long long)value);
} else {
pr_warn("unrecognized extern '%s'\n", ext->name);
return -EINVAL;
diff --git a/tools/lib/bpf/usdt.bpf.h b/tools/lib/bpf/usdt.bpf.h
index 4181fddb3687..4f2adc0bd6ca 100644
--- a/tools/lib/bpf/usdt.bpf.h
+++ b/tools/lib/bpf/usdt.bpf.h
@@ -6,7 +6,6 @@
#include <linux/errno.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>
-#include <bpf/bpf_core_read.h>
/* Below types and maps are internal implementation details of libbpf's
USDT
* support and are subjects to change. Also, bpf_usdt_xxx() API helpers
should
@@ -30,14 +29,6 @@
#ifndef BPF_USDT_MAX_IP_CNT
#define BPF_USDT_MAX_IP_CNT (4 * BPF_USDT_MAX_SPEC_CNT)
#endif
-/* We use BPF CO-RE to detect support for BPF cookie from BPF side. This
is
- * the only dependency on CO-RE, so if it's undesirable, user can
override
- * BPF_USDT_HAS_BPF_COOKIE to specify whether to BPF cookie is supported
or not.
- */
-#ifndef BPF_USDT_HAS_BPF_COOKIE
-#define BPF_USDT_HAS_BPF_COOKIE \
- bpf_core_enum_value_exists(enum bpf_func_id___usdt,
BPF_FUNC_get_attach_cookie___usdt)
-#endif
enum __bpf_usdt_arg_type {
BPF_USDT_ARG_CONST,
@@ -83,15 +74,12 @@ struct {
__type(value, __u32);
} __bpf_usdt_ip_to_spec_id SEC(".maps") __weak;
-/* don't rely on user's BPF code to have latest definition of
bpf_func_id */
-enum bpf_func_id___usdt {
- BPF_FUNC_get_attach_cookie___usdt = 0xBAD, /* value doesn't matter */
-};
+extern const _Bool LINUX_HAS_BPF_COOKIE __kconfig;
Could _Bool be a problem when used by c++? I remember that we can have
sizeof(bool) != sizeof(_Bool) when compiling with g++. If we were to
use 'int' instead I'm assuming we'll loose all the niceties of
KCFG_BOOL?
Or shouldn't be a problem since it's not part of C/C++ api boundary?
static __always_inline
int __bpf_usdt_spec_id(struct pt_regs *ctx)
{
- if (!BPF_USDT_HAS_BPF_COOKIE) {
+ if (!LINUX_HAS_BPF_COOKIE) {
long ip = PT_REGS_IP(ctx);
int *spec_id_ptr;
--
2.30.2
