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libbpf: Support pre-initializing .bss global variables 

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: eba9c5f498 ("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
This commit is contained in:
Andrii Nakryiko 2020-06-12 12:45:04 -07:00 committed by Alexei Starovoitov
parent 22eb78792e
commit caf62492f4
3 changed files with 55 additions and 13 deletions
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4
tools/lib/bpf/libbpf.c
View File

@ -3564,10 +3564,6 @@ 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;

45
tools/testing/selftests/bpf/prog_tests/skeleton.c
View File

@ -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);

19
tools/testing/selftests/bpf/progs/test_skeleton.c
View File

@ -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;