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bpf_map_def: introduce map name 'field'

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The field is actually just a compile time calculate index into pin_location.
We add a C++ only helper to return the ASCIIZ string at this offset.

Temporary abort() added to show this is equivalent.

Test: TreeHugger
Flag: EXEMPT mainline/noop
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: If57390b99f348ab03b277e8f68e7f38636c751fc
This commit is contained in:
Maciej Żenczykowski 2025-07-30 18:12:35 -07:00
commit b3dba5438d
3 changed files with 37 additions and 21 deletions
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2
bpf/loader/NetBpfLoad.cpp
View file

@ -484,6 +484,8 @@ static bool mapMatchesExpectations(const unique_fd& fd, const string& mapName,
// or a newly introduced kernel feature/bug (which is unlikely to get backported to 4.9).
if (!isAtLeastKernelVersion(4, 14, 0)) return true;
if (strcmp(mapName.c_str(), mapDef.name())) abort();
// Assuming fd is a valid Bpf Map file descriptor then
// all the following should always succeed on a 4.14+ kernel.
// If they somehow do fail, they'll return -1 (and set errno),

40
bpf/progs/include/bpf_helpers.h
View file

@ -244,26 +244,26 @@ static int (*bpf_sk_storage_delete_unsafe) (const void* sk_storage,
type == BPF_MAP_TYPE_SK_STORAGE) ? BPF_F_NO_PREALLOC : 0) \
)
#define DEFINE_BPF_MAP_BASE(the_map, TYPE, keysize, valuesize, num_entries, \
usr, grp, md, selinux, pindir, minkver, \
maxkver, minloader, maxloader, mapflags) \
VALIDATE_SELINUX_CONTEXT(minloader, selinux); \
VALIDATE_PIN_DIR(minloader, pindir); \
const struct bpf_map_def SECTION(".android_maps") the_map##_def = { \
.type = BPF_MAP_TYPE_##TYPE, \
.key_size = (keysize), \
.value_size = (valuesize), \
.max_entries = ABSOLUTE(num_entries), \
.map_flags = DEFAULT_BPF_MAP_FLAGS(BPF_MAP_TYPE_##TYPE, num_entries, mapflags), \
.uid = (usr), \
.gid = (grp), \
.mode = (md), \
.bpfloader_min_ver = (minloader), \
.bpfloader_max_ver = (maxloader), \
.min_kver = (minkver).kver, \
.max_kver = (maxkver).kver, \
.create_location = CREATE_LOCATION(selinux), \
.pin_location = "/sys/fs/bpf/" pindir "/map_" BPF_OBJ_NAME "_" #the_map, \
#define DEFINE_BPF_MAP_BASE(the_map, TYPE, keysize, valuesize, num_entries, usr, grp, md, \
selinux, pindir, minkver, maxkver, minloader, maxloader, mapflags) \
VALIDATE_SELINUX_CONTEXT(minloader, selinux); \
VALIDATE_PIN_DIR(minloader, pindir); \
const struct bpf_map_def SECTION(".android_maps") the_map##_def = { \
.type = BPF_MAP_TYPE_##TYPE, \
.key_size = (keysize), \
.value_size = (valuesize), \
.max_entries = ABSOLUTE(num_entries), \
.map_flags = DEFAULT_BPF_MAP_FLAGS(BPF_MAP_TYPE_##TYPE, num_entries, mapflags), \
.uid = (usr), \
.gid = (grp), \
.mode = (md), \
.bpfloader_min_ver = (minloader), \
.bpfloader_max_ver = (maxloader), \
.min_kver = (minkver).kver, \
.max_kver = (maxkver).kver, \
.create_location = CREATE_LOCATION(selinux), \
.pin_location = "/sys/fs/bpf/" pindir "/map_" BPF_OBJ_NAME "_" #the_map, \
.name_idx = __builtin_strlen("/sys/fs/bpf/" pindir "/map_" BPF_OBJ_NAME "_"), \
};
#define __uint(name, val) int (*name)[val]

16
bpf/progs/include/bpf_map_def.h
View file

@ -25,6 +25,10 @@
// Pull in AID_* constants from //system/core/libcutils/include/private/android_filesystem_config.h
#include <cutils/android_filesystem_config.h>
#ifdef __cplusplus
#include <type_traits>
#endif
/*
* The bpf_{map,prog}_def structures are compiled for different architectures.
* Once by the BPF compiler for the BPF architecture, and once by a C++
@ -144,11 +148,21 @@ struct bpf_map_def {
// These are fixed length ASCIIZ strings, padded with null bytes
char create_location[BPF_DEF_CHAR_ARRAY_SIZE];
char pin_location[BPF_DEF_CHAR_ARRAY_SIZE];
unsigned int name_idx;
#ifdef __cplusplus
const char * name() const { return this->pin_location + this->name_idx; }
#endif
};
#ifdef __cplusplus
static_assert(std::is_pod_v<struct bpf_map_def>);
static_assert(std::is_standard_layout_v<struct bpf_map_def>);
#endif
// This needs to be updated whenever the above structure definition is expanded.
// These asserts are here to make sure we have cross-6-arch consistency.
_Static_assert(sizeof(struct bpf_map_def) == 48 + 2 * BPF_DEF_CHAR_ARRAY_SIZE, "wrong sizeof struct bpf_map_def");
_Static_assert(sizeof(struct bpf_map_def) == 52 + 2 * BPF_DEF_CHAR_ARRAY_SIZE, "wrong sizeof struct bpf_map_def");
_Static_assert(__alignof__(struct bpf_map_def) == 4, "__alignof__ struct bpf_map_def != 4");
_Static_assert(_Alignof(struct bpf_map_def) == 4, "_Alignof struct bpf_map_def != 4");