[PATCH AUTOSEL 5.7 387/388] libbpf: Support pre-initializing .bss global variables

Sasha Levin
2020-06-18T02:28:05Z

From: Andrii Nakryiko <andriin@fb.com>

[ Upstream commit caf62492f479585296e9d636c798d5ac256b7b04 ]

Remove invalid assumption in libbpf that .bss map doesn't have to be updated
in kernel. With addition of skeleton and memory-mapped initialization image,
.bss doesn't have to be all zeroes when BPF map is created, because user-code
might have initialized those variables from user-space.

Fixes: eba9c5f498a1 ("libbpf: Refactor global data map initialization")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200612194504.557844-1-andriin@fb.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
tools/lib/bpf/libbpf.c | 4 --
.../selftests/bpf/prog_tests/skeleton.c | 45 ++++++++++++++++---
.../selftests/bpf/progs/test_skeleton.c | 19 ++++++--
3 files changed, 55 insertions(+), 13 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 8f480e29a6b0..7d80bb1fea4c 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -3455,10 +3455,6 @@ bpf_object__populate_internal_map(struct bpf_object *obj, struct bpf_map *map)
char *cp, errmsg[STRERR_BUFSIZE];
int err, zero = 0;

- /* kernel already zero-initializes .bss map. */
- if (map_type == LIBBPF_MAP_BSS)
- return 0;
-
err = bpf_map_update_elem(map->fd, &zero, map->mmaped, 0);
if (err) {
err = -errno;
diff --git a/tools/testing/selftests/bpf/prog_tests/skeleton.c b/tools/testing/selftests/bpf/prog_tests/skeleton.c
index 9264a2736018..fa153cf67b1b 100644
--- a/tools/testing/selftests/bpf/prog_tests/skeleton.c
+++ b/tools/testing/selftests/bpf/prog_tests/skeleton.c
@@ -15,6 +15,8 @@ void test_skeleton(void)
int duration = 0, err;
struct test_skeleton* skel;
struct test_skeleton__bss *bss;
+ struct test_skeleton__data *data;
+ struct test_skeleton__rodata *rodata;
struct test_skeleton__kconfig *kcfg;

skel = test_skeleton__open();
@@ -24,13 +26,45 @@ void test_skeleton(void)
if (CHECK(skel->kconfig, "skel_kconfig", "kconfig is mmaped()!\n"))
goto cleanup;

+ bss = skel->bss;
+ data = skel->data;
+ rodata = skel->rodata;
+
+ /* validate values are pre-initialized correctly */
+ CHECK(data->in1 != -1, "in1", "got %d != exp %d\n", data->in1, -1);
+ CHECK(data->out1 != -1, "out1", "got %d != exp %d\n", data->out1, -1);
+ CHECK(data->in2 != -1, "in2", "got %lld != exp %lld\n", data->in2, -1LL);
+ CHECK(data->out2 != -1, "out2", "got %lld != exp %lld\n", data->out2, -1LL);
+
+ CHECK(bss->in3 != 0, "in3", "got %d != exp %d\n", bss->in3, 0);
+ CHECK(bss->out3 != 0, "out3", "got %d != exp %d\n", bss->out3, 0);
+ CHECK(bss->in4 != 0, "in4", "got %lld != exp %lld\n", bss->in4, 0LL);
+ CHECK(bss->out4 != 0, "out4", "got %lld != exp %lld\n", bss->out4, 0LL);
+
+ CHECK(rodata->in6 != 0, "in6", "got %d != exp %d\n", rodata->in6, 0);
+ CHECK(bss->out6 != 0, "out6", "got %d != exp %d\n", bss->out6, 0);
+
+ /* validate we can pre-setup global variables, even in .bss */
+ data->in1 = 10;
+ data->in2 = 11;
+ bss->in3 = 12;
+ bss->in4 = 13;
+ rodata->in6 = 14;
+
err = test_skeleton__load(skel);
if (CHECK(err, "skel_load", "failed to load skeleton: %d\n", err))
goto cleanup;

- bss = skel->bss;
- bss->in1 = 1;
- bss->in2 = 2;
+ /* validate pre-setup values are still there */
+ CHECK(data->in1 != 10, "in1", "got %d != exp %d\n", data->in1, 10);
+ CHECK(data->in2 != 11, "in2", "got %lld != exp %lld\n", data->in2, 11LL);
+ CHECK(bss->in3 != 12, "in3", "got %d != exp %d\n", bss->in3, 12);
+ CHECK(bss->in4 != 13, "in4", "got %lld != exp %lld\n", bss->in4, 13LL);
+ CHECK(rodata->in6 != 14, "in6", "got %d != exp %d\n", rodata->in6, 14);
+
+ /* now set new values and attach to get them into outX variables */
+ data->in1 = 1;
+ data->in2 = 2;
bss->in3 = 3;
bss->in4 = 4;
bss->in5.a = 5;
@@ -44,14 +78,15 @@ void test_skeleton(void)
/* trigger tracepoint */
usleep(1);

- CHECK(bss->out1 != 1, "res1", "got %d != exp %d\n", bss->out1, 1);
- CHECK(bss->out2 != 2, "res2", "got %lld != exp %d\n", bss->out2, 2);
+ CHECK(data->out1 != 1, "res1", "got %d != exp %d\n", data->out1, 1);
+ CHECK(data->out2 != 2, "res2", "got %lld != exp %d\n", data->out2, 2);
CHECK(bss->out3 != 3, "res3", "got %d != exp %d\n", (int)bss->out3, 3);
CHECK(bss->out4 != 4, "res4", "got %lld != exp %d\n", bss->out4, 4);
CHECK(bss->handler_out5.a != 5, "res5", "got %d != exp %d\n",
bss->handler_out5.a, 5);
CHECK(bss->handler_out5.b != 6, "res6", "got %lld != exp %d\n",
bss->handler_out5.b, 6);
+ CHECK(bss->out6 != 14, "res7", "got %d != exp %d\n", bss->out6, 14);

CHECK(bss->bpf_syscall != kcfg->CONFIG_BPF_SYSCALL, "ext1",
"got %d != exp %d\n", bss->bpf_syscall, kcfg->CONFIG_BPF_SYSCALL);
diff --git a/tools/testing/selftests/bpf/progs/test_skeleton.c b/tools/testing/selftests/bpf/progs/test_skeleton.c
index de03a90f78ca..77ae86f44db5 100644
--- a/tools/testing/selftests/bpf/progs/test_skeleton.c
+++ b/tools/testing/selftests/bpf/progs/test_skeleton.c
@@ -10,16 +10,26 @@ struct s {
long long b;
} __attribute__((packed));

-int in1 = 0;
-long long in2 = 0;
+/* .data section */
+int in1 = -1;
+long long in2 = -1;
+
+/* .bss section */
char in3 = '\0';
long long in4 __attribute__((aligned(64))) = 0;
struct s in5 = {};

-long long out2 = 0;
+/* .rodata section */
+const volatile int in6 = 0;
+
+/* .data section */
+int out1 = -1;
+long long out2 = -1;
+
+/* .bss section */
char out3 = 0;
long long out4 = 0;
-int out1 = 0;
+int out6 = 0;

extern bool CONFIG_BPF_SYSCALL __kconfig;
extern int LINUX_KERNEL_VERSION __kconfig;
@@ -36,6 +46,7 @@ int handler(const void *ctx)
out3 = in3;
out4 = in4;
out5 = in5;
+ out6 = in6;

bpf_syscall = CONFIG_BPF_SYSCALL;
kern_ver = LINUX_KERNEL_VERSION;
--
2.25.1