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libbpf: Put Kconfig externs into .kconfig section
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Move Kconfig-provided externs into custom .kconfig section. Add __kconfig into
bpf_helpers.h for user convenience. Update selftests accordingly.

Suggested-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20191219002837.3074619-2-andriin@fb.com
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Andrii Nakryiko authored and Alexei Starovoitov committed Dec 19, 2019
1 parent d695870 commit 81bfdd0
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Showing 6 changed files with 60 additions and 48 deletions.
8 changes: 4 additions & 4 deletions tools/bpf/bpftool/gen.c
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Original file line number Diff line number Diff line change
Expand Up @@ -83,8 +83,8 @@ static const char *get_map_ident(const struct bpf_map *map)
return "rodata";
else if (str_has_suffix(name, ".bss"))
return "bss";
else if (str_has_suffix(name, ".extern"))
return "externs"; /* extern is a C keyword */
else if (str_has_suffix(name, ".kconfig"))
return "kconfig";
else
return NULL;
}
Expand Down Expand Up @@ -112,8 +112,8 @@ static int codegen_datasec_def(struct bpf_object *obj,
sec_ident = "bss";
else if (strcmp(sec_name, ".rodata") == 0)
sec_ident = "rodata";
else if (strcmp(sec_name, ".extern") == 0)
sec_ident = "externs"; /* extern is a C keyword */
else if (strcmp(sec_name, ".kconfig") == 0)
sec_ident = "kconfig";
else
return 0;

Expand Down
2 changes: 2 additions & 0 deletions tools/lib/bpf/bpf_helpers.h
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Original file line number Diff line number Diff line change
Expand Up @@ -53,4 +53,6 @@ enum libbpf_tristate {
TRI_MODULE = 2,
};

#define __kconfig __attribute__((section(".kconfig")))

#endif
58 changes: 35 additions & 23 deletions tools/lib/bpf/libbpf.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -231,21 +231,21 @@ struct bpf_program {
#define DATA_SEC ".data"
#define BSS_SEC ".bss"
#define RODATA_SEC ".rodata"
#define EXTERN_SEC ".extern"
#define KCONFIG_SEC ".kconfig"

enum libbpf_map_type {
LIBBPF_MAP_UNSPEC,
LIBBPF_MAP_DATA,
LIBBPF_MAP_BSS,
LIBBPF_MAP_RODATA,
LIBBPF_MAP_EXTERN,
LIBBPF_MAP_KCONFIG,
};

static const char * const libbpf_type_to_btf_name[] = {
[LIBBPF_MAP_DATA] = DATA_SEC,
[LIBBPF_MAP_BSS] = BSS_SEC,
[LIBBPF_MAP_RODATA] = RODATA_SEC,
[LIBBPF_MAP_EXTERN] = EXTERN_SEC,
[LIBBPF_MAP_KCONFIG] = KCONFIG_SEC,
};

struct bpf_map {
Expand Down Expand Up @@ -305,7 +305,7 @@ struct bpf_object {
char *kconfig_path;
struct extern_desc *externs;
int nr_extern;
int extern_map_idx;
int kconfig_map_idx;

bool loaded;
bool has_pseudo_calls;
Expand Down Expand Up @@ -606,7 +606,7 @@ static struct bpf_object *bpf_object__new(const char *path,
obj->efile.data_shndx = -1;
obj->efile.rodata_shndx = -1;
obj->efile.bss_shndx = -1;
obj->extern_map_idx = -1;
obj->kconfig_map_idx = -1;

obj->kern_version = get_kernel_version();
obj->loaded = false;
Expand Down Expand Up @@ -902,11 +902,25 @@ static size_t bpf_map_mmap_sz(const struct bpf_map *map)
return map_sz;
}

static char *internal_map_name(struct bpf_object *obj,
enum libbpf_map_type type)
{
char map_name[BPF_OBJ_NAME_LEN];
const char *sfx = libbpf_type_to_btf_name[type];
int sfx_len = max((size_t)7, strlen(sfx));
int pfx_len = min((size_t)BPF_OBJ_NAME_LEN - sfx_len - 1,
strlen(obj->name));

snprintf(map_name, sizeof(map_name), "%.*s%.*s", pfx_len, obj->name,
sfx_len, libbpf_type_to_btf_name[type]);

return strdup(map_name);
}

static int
bpf_object__init_internal_map(struct bpf_object *obj, enum libbpf_map_type type,
int sec_idx, void *data, size_t data_sz)
{
char map_name[BPF_OBJ_NAME_LEN];
struct bpf_map_def *def;
struct bpf_map *map;
int err;
Expand All @@ -918,9 +932,7 @@ bpf_object__init_internal_map(struct bpf_object *obj, enum libbpf_map_type type,
map->libbpf_type = type;
map->sec_idx = sec_idx;
map->sec_offset = 0;
snprintf(map_name, sizeof(map_name), "%.8s%.7s", obj->name,
libbpf_type_to_btf_name[type]);
map->name = strdup(map_name);
map->name = internal_map_name(obj, type);
if (!map->name) {
pr_warn("failed to alloc map name\n");
return -ENOMEM;
Expand All @@ -931,12 +943,12 @@ bpf_object__init_internal_map(struct bpf_object *obj, enum libbpf_map_type type,
def->key_size = sizeof(int);
def->value_size = data_sz;
def->max_entries = 1;
def->map_flags = type == LIBBPF_MAP_RODATA || type == LIBBPF_MAP_EXTERN
def->map_flags = type == LIBBPF_MAP_RODATA || type == LIBBPF_MAP_KCONFIG
? BPF_F_RDONLY_PROG : 0;
def->map_flags |= BPF_F_MMAPABLE;

pr_debug("map '%s' (global data): at sec_idx %d, offset %zu, flags %x.\n",
map_name, map->sec_idx, map->sec_offset, def->map_flags);
map->name, map->sec_idx, map->sec_offset, def->map_flags);

map->mmaped = mmap(NULL, bpf_map_mmap_sz(map), PROT_READ | PROT_WRITE,
MAP_SHARED | MAP_ANONYMOUS, -1, 0);
Expand Down Expand Up @@ -1232,7 +1244,7 @@ static int bpf_object__read_kernel_config(struct bpf_object *obj,
return err;
}

static int bpf_object__init_extern_map(struct bpf_object *obj)
static int bpf_object__init_kconfig_map(struct bpf_object *obj)
{
struct extern_desc *last_ext;
size_t map_sz;
Expand All @@ -1244,13 +1256,13 @@ static int bpf_object__init_extern_map(struct bpf_object *obj)
last_ext = &obj->externs[obj->nr_extern - 1];
map_sz = last_ext->data_off + last_ext->sz;

err = bpf_object__init_internal_map(obj, LIBBPF_MAP_EXTERN,
err = bpf_object__init_internal_map(obj, LIBBPF_MAP_KCONFIG,
obj->efile.symbols_shndx,
NULL, map_sz);
if (err)
return err;

obj->extern_map_idx = obj->nr_maps - 1;
obj->kconfig_map_idx = obj->nr_maps - 1;

return 0;
}
Expand Down Expand Up @@ -1742,7 +1754,7 @@ static int bpf_object__init_maps(struct bpf_object *obj,
err = bpf_object__init_user_maps(obj, strict);
err = err ?: bpf_object__init_user_btf_maps(obj, strict, pin_root_path);
err = err ?: bpf_object__init_global_data_maps(obj);
err = err ?: bpf_object__init_extern_map(obj);
err = err ?: bpf_object__init_kconfig_map(obj);
if (err)
return err;

Expand Down Expand Up @@ -2269,9 +2281,9 @@ static int bpf_object__collect_externs(struct bpf_object *obj)
i, ext->sym_idx, ext->data_off, ext->name);
}

btf_id = btf__find_by_name(obj->btf, EXTERN_SEC);
btf_id = btf__find_by_name(obj->btf, KCONFIG_SEC);
if (btf_id <= 0) {
pr_warn("no BTF info found for '%s' datasec\n", EXTERN_SEC);
pr_warn("no BTF info found for '%s' datasec\n", KCONFIG_SEC);
return -ESRCH;
}

Expand Down Expand Up @@ -2361,7 +2373,7 @@ bpf_object__section_to_libbpf_map_type(const struct bpf_object *obj, int shndx)
else if (shndx == obj->efile.rodata_shndx)
return LIBBPF_MAP_RODATA;
else if (shndx == obj->efile.symbols_shndx)
return LIBBPF_MAP_EXTERN;
return LIBBPF_MAP_KCONFIG;
else
return LIBBPF_MAP_UNSPEC;
}
Expand Down Expand Up @@ -2908,8 +2920,8 @@ bpf_object__populate_internal_map(struct bpf_object *obj, struct bpf_map *map)
return err;
}

/* Freeze .rodata and .extern map as read-only from syscall side. */
if (map_type == LIBBPF_MAP_RODATA || map_type == LIBBPF_MAP_EXTERN) {
/* Freeze .rodata and .kconfig map as read-only from syscall side. */
if (map_type == LIBBPF_MAP_RODATA || map_type == LIBBPF_MAP_KCONFIG) {
err = bpf_map_freeze(map->fd);
if (err) {
err = -errno;
Expand Down Expand Up @@ -4264,7 +4276,7 @@ bpf_program__relocate(struct bpf_program *prog, struct bpf_object *obj)
break;
case RELO_EXTERN:
insn[0].src_reg = BPF_PSEUDO_MAP_VALUE;
insn[0].imm = obj->maps[obj->extern_map_idx].fd;
insn[0].imm = obj->maps[obj->kconfig_map_idx].fd;
insn[1].imm = relo->sym_off;
break;
case RELO_CALL:
Expand Down Expand Up @@ -4743,7 +4755,7 @@ static int bpf_object__resolve_externs(struct bpf_object *obj,
if (obj->nr_extern == 0)
return 0;

data = obj->maps[obj->extern_map_idx].mmaped;
data = obj->maps[obj->kconfig_map_idx].mmaped;

for (i = 0; i < obj->nr_extern; i++) {
ext = &obj->externs[i];
Expand Down Expand Up @@ -7546,7 +7558,7 @@ int bpf_object__open_skeleton(struct bpf_object_skeleton *s,
}

/* externs shouldn't be pre-setup from user code */
if (mmaped && (*map)->libbpf_type != LIBBPF_MAP_EXTERN)
if (mmaped && (*map)->libbpf_type != LIBBPF_MAP_KCONFIG)
*mmaped = (*map)->mmaped;
}

Expand Down
16 changes: 7 additions & 9 deletions tools/testing/selftests/bpf/prog_tests/skeleton.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -15,20 +15,18 @@ void test_skeleton(void)
int duration = 0, err;
struct test_skeleton* skel;
struct test_skeleton__bss *bss;
struct test_skeleton__externs *exts;
struct test_skeleton__kconfig *kcfg;

skel = test_skeleton__open();
if (CHECK(!skel, "skel_open", "failed to open skeleton\n"))
return;

printf("EXTERNS BEFORE: %p\n", skel->externs);
if (CHECK(skel->externs, "skel_externs", "externs are mmaped()!\n"))
if (CHECK(skel->kconfig, "skel_kconfig", "kconfig is mmaped()!\n"))
goto cleanup;

err = test_skeleton__load(skel);
if (CHECK(err, "skel_load", "failed to load skeleton: %d\n", err))
goto cleanup;
printf("EXTERNS AFTER: %p\n", skel->externs);

bss = skel->bss;
bss->in1 = 1;
Expand All @@ -37,7 +35,7 @@ void test_skeleton(void)
bss->in4 = 4;
bss->in5.a = 5;
bss->in5.b = 6;
exts = skel->externs;
kcfg = skel->kconfig;

err = test_skeleton__attach(skel);
if (CHECK(err, "skel_attach", "skeleton attach failed: %d\n", err))
Expand All @@ -55,10 +53,10 @@ void test_skeleton(void)
CHECK(bss->handler_out5.b != 6, "res6", "got %lld != exp %d\n",
bss->handler_out5.b, 6);

CHECK(bss->bpf_syscall != exts->CONFIG_BPF_SYSCALL, "ext1",
"got %d != exp %d\n", bss->bpf_syscall, exts->CONFIG_BPF_SYSCALL);
CHECK(bss->kern_ver != exts->LINUX_KERNEL_VERSION, "ext2",
"got %d != exp %d\n", bss->kern_ver, exts->LINUX_KERNEL_VERSION);
CHECK(bss->bpf_syscall != kcfg->CONFIG_BPF_SYSCALL, "ext1",
"got %d != exp %d\n", bss->bpf_syscall, kcfg->CONFIG_BPF_SYSCALL);
CHECK(bss->kern_ver != kcfg->LINUX_KERNEL_VERSION, "ext2",
"got %d != exp %d\n", bss->kern_ver, kcfg->LINUX_KERNEL_VERSION);

cleanup:
test_skeleton__destroy(skel);
Expand Down
20 changes: 10 additions & 10 deletions tools/testing/selftests/bpf/progs/test_core_extern.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -10,16 +10,16 @@
/* non-existing BPF helper, to test dead code elimination */
static int (*bpf_missing_helper)(const void *arg1, int arg2) = (void *) 999;

extern int LINUX_KERNEL_VERSION;
extern bool CONFIG_BPF_SYSCALL; /* strong */
extern enum libbpf_tristate CONFIG_TRISTATE __weak;
extern bool CONFIG_BOOL __weak;
extern char CONFIG_CHAR __weak;
extern uint16_t CONFIG_USHORT __weak;
extern int CONFIG_INT __weak;
extern uint64_t CONFIG_ULONG __weak;
extern const char CONFIG_STR[8] __weak;
extern uint64_t CONFIG_MISSING __weak;
extern int LINUX_KERNEL_VERSION __kconfig;
extern bool CONFIG_BPF_SYSCALL __kconfig; /* strong */
extern enum libbpf_tristate CONFIG_TRISTATE __kconfig __weak;
extern bool CONFIG_BOOL __kconfig __weak;
extern char CONFIG_CHAR __kconfig __weak;
extern uint16_t CONFIG_USHORT __kconfig __weak;
extern int CONFIG_INT __kconfig __weak;
extern uint64_t CONFIG_ULONG __kconfig __weak;
extern const char CONFIG_STR[8] __kconfig __weak;
extern uint64_t CONFIG_MISSING __kconfig __weak;

uint64_t kern_ver = -1;
uint64_t bpf_syscall = -1;
Expand Down
4 changes: 2 additions & 2 deletions tools/testing/selftests/bpf/progs/test_skeleton.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -21,8 +21,8 @@ char out3 = 0;
long long out4 = 0;
int out1 = 0;

extern bool CONFIG_BPF_SYSCALL;
extern int LINUX_KERNEL_VERSION;
extern bool CONFIG_BPF_SYSCALL __kconfig;
extern int LINUX_KERNEL_VERSION __kconfig;
bool bpf_syscall = 0;
int kern_ver = 0;

Expand Down

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