Commit caf62492 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
Browse files

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: eba9c5f4 ("libbpf: Refactor global data map initialization")
Signed-off-by: default avatarAndrii Nakryiko <andriin@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200612194504.557844-1-andriin@fb.com
parent 22eb7879

tools/lib/bpf/libbpf.c

+0 −4
Original line number Diff line number Diff line
@@ -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;

tools/testing/selftests/bpf/prog_tests/skeleton.c

+40 −5
Original line number Diff line number Diff line
@@ -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);

tools/testing/selftests/bpf/progs/test_skeleton.c

+15 −4
Original line number Diff line number Diff line
@@ -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;

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