* [PATCH bpf-next 1/2] libbpf: load global data maps lazily on legacy kernels
@ 2021-11-20 1:14 Andrii Nakryiko
2021-11-20 1:14 ` [PATCH bpf-next 2/2] selftests/bpf: mix legacy (maps) and modern (vars) BPF in one test Andrii Nakryiko
2021-11-20 7:31 ` [PATCH bpf-next 1/2] libbpf: load global data maps lazily on legacy kernels Song Liu
0 siblings, 2 replies; 4+ messages in thread
From: Andrii Nakryiko @ 2021-11-20 1:14 UTC (permalink / raw)
To: bpf, ast, daniel; +Cc: andrii, kernel-team
Load global data maps lazily, if kernel is too old to support global
data. Make sure that programs are still correct by detecting if any of
the to-be-loaded programs have relocation against any of such maps.
This allows to solve the issue ([0]) with bpf_printk() and Clang
generating unnecessary and unreferenced .rodata.strX.Y sections, but it
also goes further along the CO-RE lines, allowing to have a BPF object
in which some code can work on very old kernels and relies only on BPF
maps explicitly, while other BPF programs might enjoy global variable
support. If such programs are correctly set to not load at runtime on
old kernels, bpf_object will load and function correctly now.
[0] https://lore.kernel.org/bpf/CAK-59YFPU3qO+_pXWOH+c1LSA=8WA1yabJZfREjOEXNHAqgXNg@mail.gmail.com/
Fixes: aed659170a31 ("libbpf: Support multiple .rodata.* and .data.* BPF maps")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
tools/lib/bpf/libbpf.c | 34 ++++++++++++++++++++++++++++++----
1 file changed, 30 insertions(+), 4 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index af405c38aadc..27695bf31250 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -5006,6 +5006,24 @@ bpf_object__create_maps(struct bpf_object *obj)
for (i = 0; i < obj->nr_maps; i++) {
map = &obj->maps[i];
+ /* To support old kernels, we skip creating global data maps
+ * (.rodata, .data, .kconfig, etc); later on, during program
+ * loading, if we detect that at least one of the to-be-loaded
+ * programs is referencing any global data map, we'll error
+ * out with program name and relocation index logged.
+ * This approach allows to accommodate Clang emitting
+ * unnecessary .rodata.str1.1 sections for string literals,
+ * but also it allows to have CO-RE applications that use
+ * global variables in some of BPF programs, but not others.
+ * If those global variable-using programs are not loaded at
+ * runtime due to bpf_program__set_autoload(prog, false),
+ * bpf_object loading will succeed just fine even on old
+ * kernels.
+ */
+ if (bpf_map__is_internal(map) &&
+ !kernel_supports(obj, FEAT_GLOBAL_DATA))
+ continue;
+
retried = false;
retry:
if (map->pin_path) {
@@ -5605,6 +5623,14 @@ bpf_object__relocate_data(struct bpf_object *obj, struct bpf_program *prog)
insn[0].src_reg = BPF_PSEUDO_MAP_IDX_VALUE;
insn[0].imm = relo->map_idx;
} else {
+ const struct bpf_map *map = &obj->maps[relo->map_idx];
+
+ if (bpf_map__is_internal(map) &&
+ !kernel_supports(obj, FEAT_GLOBAL_DATA)) {
+ pr_warn("prog '%s': relo #%d: kernel doesn't support global data\n",
+ prog->name, i);
+ return -ENOTSUP;
+ }
insn[0].src_reg = BPF_PSEUDO_MAP_VALUE;
insn[0].imm = obj->maps[relo->map_idx].fd;
}
@@ -6139,6 +6165,8 @@ bpf_object__relocate(struct bpf_object *obj, const char *targ_btf_path)
*/
if (prog_is_subprog(obj, prog))
continue;
+ if (!prog->load)
+ continue;
err = bpf_object__relocate_calls(obj, prog);
if (err) {
@@ -6152,6 +6180,8 @@ bpf_object__relocate(struct bpf_object *obj, const char *targ_btf_path)
prog = &obj->programs[i];
if (prog_is_subprog(obj, prog))
continue;
+ if (!prog->load)
+ continue;
err = bpf_object__relocate_data(obj, prog);
if (err) {
pr_warn("prog '%s': failed to relocate data references: %d\n",
@@ -6939,10 +6969,6 @@ static int bpf_object__sanitize_maps(struct bpf_object *obj)
bpf_object__for_each_map(m, obj) {
if (!bpf_map__is_internal(m))
continue;
- if (!kernel_supports(obj, FEAT_GLOBAL_DATA)) {
- pr_warn("kernel doesn't support global data\n");
- return -ENOTSUP;
- }
if (!kernel_supports(obj, FEAT_ARRAY_MMAP))
m->def.map_flags ^= BPF_F_MMAPABLE;
}
--
2.30.2
^ permalink raw reply related [flat|nested] 4+ messages in thread
* [PATCH bpf-next 2/2] selftests/bpf: mix legacy (maps) and modern (vars) BPF in one test
2021-11-20 1:14 [PATCH bpf-next 1/2] libbpf: load global data maps lazily on legacy kernels Andrii Nakryiko
@ 2021-11-20 1:14 ` Andrii Nakryiko
2021-11-20 7:43 ` Song Liu
2021-11-20 7:31 ` [PATCH bpf-next 1/2] libbpf: load global data maps lazily on legacy kernels Song Liu
1 sibling, 1 reply; 4+ messages in thread
From: Andrii Nakryiko @ 2021-11-20 1:14 UTC (permalink / raw)
To: bpf, ast, daniel; +Cc: andrii, kernel-team
Add selftest that combines two BPF programs within single BPF object
file such that one of the programs is using global variables, but can be
skipped at runtime on old kernels that don't support global data.
Another BPF program is written with the goal to be runnable on very old
kernels and only relies on explicitly accessed BPF maps.
Such test, run against old kernels (e.g., libbpf CI will run it against 4.9
kernel that doesn't support global data), allows to test the approach
and ensure that libbpf doesn't make unnecessary assumption about
necessary kernel features.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
.../selftests/bpf/prog_tests/legacy_printk.c | 65 +++++++++++++++++++
.../selftests/bpf/progs/test_legacy_printk.c | 65 +++++++++++++++++++
2 files changed, 130 insertions(+)
create mode 100644 tools/testing/selftests/bpf/prog_tests/legacy_printk.c
create mode 100644 tools/testing/selftests/bpf/progs/test_legacy_printk.c
diff --git a/tools/testing/selftests/bpf/prog_tests/legacy_printk.c b/tools/testing/selftests/bpf/prog_tests/legacy_printk.c
new file mode 100644
index 000000000000..ec6e45f2a644
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/legacy_printk.c
@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+#include <test_progs.h>
+#include "test_legacy_printk.skel.h"
+
+static int execute_one_variant(bool legacy)
+{
+ struct test_legacy_printk *skel;
+ int err, zero = 0, my_pid = getpid(), res, map_fd;
+
+ skel = test_legacy_printk__open();
+ if (!ASSERT_OK_PTR(skel, "skel_open"))
+ return -errno;
+
+ bpf_program__set_autoload(skel->progs.handle_legacy, legacy);
+ bpf_program__set_autoload(skel->progs.handle_modern, !legacy);
+
+ err = test_legacy_printk__load(skel);
+ /* no ASSERT_OK, we expect one of two variants can fail here */
+ if (err)
+ goto err_out;
+
+ if (legacy) {
+ map_fd = bpf_map__fd(skel->maps.my_pid_map);
+ err = bpf_map_update_elem(map_fd, &zero, &my_pid, BPF_ANY);
+ if (!ASSERT_OK(err, "my_pid_map_update"))
+ goto err_out;
+ err = bpf_map_lookup_elem(map_fd, &zero, &res);
+ } else {
+ skel->bss->my_pid_var = my_pid;
+ }
+
+ err = test_legacy_printk__attach(skel);
+ if (!ASSERT_OK(err, "skel_attach"))
+ goto err_out;
+
+ usleep(1); /* trigger */
+
+ if (legacy) {
+ map_fd = bpf_map__fd(skel->maps.res_map);
+ err = bpf_map_lookup_elem(map_fd, &zero, &res);
+ if (!ASSERT_OK(err, "res_map_lookup"))
+ goto err_out;
+ } else {
+ res = skel->bss->res_var;
+ }
+
+ if (!ASSERT_GT(res, 0, "res")) {
+ err = -EINVAL;
+ goto err_out;
+ }
+
+err_out:
+ test_legacy_printk__destroy(skel);
+ return err;
+}
+
+void test_legacy_printk(void)
+{
+ /* legacy variant should work everywhere */
+ ASSERT_OK(execute_one_variant(true /* legacy */), "legacy_case");
+
+ /* execute modern variant, can fail the load on old kernels */
+ execute_one_variant(false);
+}
diff --git a/tools/testing/selftests/bpf/progs/test_legacy_printk.c b/tools/testing/selftests/bpf/progs/test_legacy_printk.c
new file mode 100644
index 000000000000..96d945781e77
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_legacy_printk.c
@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include <linux/bpf.h>
+#define BPF_NO_GLOBAL_DATA
+#include <bpf/bpf_helpers.h>
+
+char LICENSE[] SEC("license") = "GPL";
+
+struct {
+ __uint(type, BPF_MAP_TYPE_ARRAY);
+ __type(key, int);
+ __type(value, int);
+ __uint(max_entries, 1);
+} my_pid_map SEC(".maps");
+
+struct {
+ __uint(type, BPF_MAP_TYPE_ARRAY);
+ __type(key, int);
+ __type(value, int);
+ __uint(max_entries, 1);
+} res_map SEC(".maps");
+
+volatile int my_pid_var = 0;
+volatile int res_var = 0;
+
+SEC("tp/raw_syscalls/sys_enter")
+int handle_legacy(void *ctx)
+{
+ int zero = 0, *my_pid, cur_pid, *my_res;
+
+ my_pid = bpf_map_lookup_elem(&my_pid_map, &zero);
+ if (!my_pid)
+ return 1;
+
+ cur_pid = bpf_get_current_pid_tgid() >> 32;
+ if (cur_pid != *my_pid)
+ return 1;
+
+ my_res = bpf_map_lookup_elem(&res_map, &zero);
+ if (!my_res)
+ return 1;
+
+ if (*my_res == 0)
+ bpf_printk("Legacy-case bpf_printk test, pid %d\n", cur_pid);
+ *my_res = 1;
+
+ return *my_res;
+}
+
+SEC("tp/raw_syscalls/sys_enter")
+int handle_modern(void *ctx)
+{
+ int zero = 0, cur_pid;
+
+ cur_pid = bpf_get_current_pid_tgid() >> 32;
+ if (cur_pid != my_pid_var)
+ return 1;
+
+ if (res_var == 0)
+ bpf_printk("Modern-case bpf_printk test, pid %d\n", cur_pid);
+ res_var = 1;
+
+ return res_var;
+}
--
2.30.2
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH bpf-next 1/2] libbpf: load global data maps lazily on legacy kernels
2021-11-20 1:14 [PATCH bpf-next 1/2] libbpf: load global data maps lazily on legacy kernels Andrii Nakryiko
2021-11-20 1:14 ` [PATCH bpf-next 2/2] selftests/bpf: mix legacy (maps) and modern (vars) BPF in one test Andrii Nakryiko
@ 2021-11-20 7:31 ` Song Liu
1 sibling, 0 replies; 4+ messages in thread
From: Song Liu @ 2021-11-20 7:31 UTC (permalink / raw)
To: Andrii Nakryiko
Cc: bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net,
Kernel Team
> On Nov 19, 2021, at 3:14 PM, Andrii Nakryiko <andrii@kernel.org> wrote:
>
> Load global data maps lazily, if kernel is too old to support global
> data. Make sure that programs are still correct by detecting if any of
> the to-be-loaded programs have relocation against any of such maps.
>
> This allows to solve the issue ([0]) with bpf_printk() and Clang
> generating unnecessary and unreferenced .rodata.strX.Y sections, but it
> also goes further along the CO-RE lines, allowing to have a BPF object
> in which some code can work on very old kernels and relies only on BPF
> maps explicitly, while other BPF programs might enjoy global variable
> support. If such programs are correctly set to not load at runtime on
> old kernels, bpf_object will load and function correctly now.'
>
> [0] https://lore.kernel.org/bpf/CAK-59YFPU3qO+_pXWOH+c1LSA=8WA1yabJZfREjOEXNHAqgXNg@mail.gmail.com/
>
> Fixes: aed659170a31 ("libbpf: Support multiple .rodata.* and .data.* BPF maps")
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH bpf-next 2/2] selftests/bpf: mix legacy (maps) and modern (vars) BPF in one test
2021-11-20 1:14 ` [PATCH bpf-next 2/2] selftests/bpf: mix legacy (maps) and modern (vars) BPF in one test Andrii Nakryiko
@ 2021-11-20 7:43 ` Song Liu
0 siblings, 0 replies; 4+ messages in thread
From: Song Liu @ 2021-11-20 7:43 UTC (permalink / raw)
To: Andrii Nakryiko
Cc: bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net,
Kernel Team
> On Nov 19, 2021, at 3:14 PM, Andrii Nakryiko <andrii@kernel.org> wrote:
>
> Add selftest that combines two BPF programs within single BPF object
> file such that one of the programs is using global variables, but can be
> skipped at runtime on old kernels that don't support global data.
> Another BPF program is written with the goal to be runnable on very old
> kernels and only relies on explicitly accessed BPF maps.
>
> Such test, run against old kernels (e.g., libbpf CI will run it against 4.9
> kernel that doesn't support global data), allows to test the approach
> and ensure that libbpf doesn't make unnecessary assumption about
> necessary kernel features.
>
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
With one nit below.
> ---
> .../selftests/bpf/prog_tests/legacy_printk.c | 65 +++++++++++++++++++
> .../selftests/bpf/progs/test_legacy_printk.c | 65 +++++++++++++++++++
> 2 files changed, 130 insertions(+)
> create mode 100644 tools/testing/selftests/bpf/prog_tests/legacy_printk.c
> create mode 100644 tools/testing/selftests/bpf/progs/test_legacy_printk.c
>
[...]
> +SEC("tp/raw_syscalls/sys_enter")
> +int handle_legacy(void *ctx)
> +{
> + int zero = 0, *my_pid, cur_pid, *my_res;
> +
> + my_pid = bpf_map_lookup_elem(&my_pid_map, &zero);
> + if (!my_pid)
> + return 1;
> +
> + cur_pid = bpf_get_current_pid_tgid() >> 32;
> + if (cur_pid != *my_pid)
> + return 1;
> +
> + my_res = bpf_map_lookup_elem(&res_map, &zero);
> + if (!my_res)
> + return 1;
> +
> + if (*my_res == 0)
> + bpf_printk("Legacy-case bpf_printk test, pid %d\n", cur_pid);
I think we discourage bpf_printk in selftests in general, but we do need the
bpf_printk here. So maybe add a comment here (and below) to explain the case?
Thanks,
Song
> + *my_res = 1;
> +
> + return *my_res;
> +}
> +
> +SEC("tp/raw_syscalls/sys_enter")
> +int handle_modern(void *ctx)
> +{
> + int zero = 0, cur_pid;
> +
> + cur_pid = bpf_get_current_pid_tgid() >> 32;
> + if (cur_pid != my_pid_var)
> + return 1;
> +
> + if (res_var == 0)
> + bpf_printk("Modern-case bpf_printk test, pid %d\n", cur_pid);
> + res_var = 1;
> +
> + return res_var;
> +}
> --
> 2.30.2
>
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2021-11-20 7:43 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz follow: Atom feed
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2021-11-20 1:14 [PATCH bpf-next 1/2] libbpf: load global data maps lazily on legacy kernels Andrii Nakryiko
2021-11-20 1:14 ` [PATCH bpf-next 2/2] selftests/bpf: mix legacy (maps) and modern (vars) BPF in one test Andrii Nakryiko
2021-11-20 7:43 ` Song Liu
2021-11-20 7:31 ` [PATCH bpf-next 1/2] libbpf: load global data maps lazily on legacy kernels Song Liu
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