bpf: rearrange bpf_func_state fields to save a bit of memory

It's a trivial rearrangement saving 8 bytes. We have 4 bytes of padding
at the end which can be filled with another field without increasing
struct bpf_func_state.

copy_func_state() logic remains correct without any further changes.

BEFORE
======
struct bpf_func_state {
        struct bpf_reg_state       regs[11];             /*     0  1320 */
        /* --- cacheline 20 boundary (1280 bytes) was 40 bytes ago --- */
        int                        callsite;             /*  1320     4 */
        u32                        frameno;              /*  1324     4 */
        u32                        subprogno;            /*  1328     4 */
        u32                        async_entry_cnt;      /*  1332     4 */
        bool                       in_callback_fn;       /*  1336     1 */

        /* XXX 7 bytes hole, try to pack */

        /* --- cacheline 21 boundary (1344 bytes) --- */
        struct tnum                callback_ret_range;   /*  1344    16 */
        bool                       in_async_callback_fn; /*  1360     1 */
        bool                       in_exception_callback_fn; /*  1361     1 */

        /* XXX 2 bytes hole, try to pack */

        int                        acquired_refs;        /*  1364     4 */
        struct bpf_reference_state * refs;               /*  1368     8 */
        int                        allocated_stack;      /*  1376     4 */

        /* XXX 4 bytes hole, try to pack */

        struct bpf_stack_state *   stack;                /*  1384     8 */

        /* size: 1392, cachelines: 22, members: 13 */
        /* sum members: 1379, holes: 3, sum holes: 13 */
        /* last cacheline: 48 bytes */
};

AFTER
=====
struct bpf_func_state {
        struct bpf_reg_state       regs[11];             /*     0  1320 */
        /* --- cacheline 20 boundary (1280 bytes) was 40 bytes ago --- */
        int                        callsite;             /*  1320     4 */
        u32                        frameno;              /*  1324     4 */
        u32                        subprogno;            /*  1328     4 */
        u32                        async_entry_cnt;      /*  1332     4 */
        struct tnum                callback_ret_range;   /*  1336    16 */
        /* --- cacheline 21 boundary (1344 bytes) was 8 bytes ago --- */
        bool                       in_callback_fn;       /*  1352     1 */
        bool                       in_async_callback_fn; /*  1353     1 */
        bool                       in_exception_callback_fn; /*  1354     1 */

        /* XXX 1 byte hole, try to pack */

        int                        acquired_refs;        /*  1356     4 */
        struct bpf_reference_state * refs;               /*  1360     8 */
        struct bpf_stack_state *   stack;                /*  1368     8 */
        int                        allocated_stack;      /*  1376     4 */

        /* size: 1384, cachelines: 22, members: 13 */
        /* sum members: 1379, holes: 1, sum holes: 1 */
        /* padding: 4 */
        /* last cacheline: 40 bytes */
};
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231202175705.885270-2-andrii@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/bpf_verifier.h

@@ -297,8 +297,8 @@ struct bpf_func_state {
 	 * void foo(void) { bpf_timer_set_callback(,foo); }
 	 */
 	u32 async_entry_cnt;
-	bool in_callback_fn;
 	struct tnum callback_ret_range;
+	bool in_callback_fn;
 	bool in_async_callback_fn;
 	bool in_exception_callback_fn;
 	/* For callback calling functions that limit number of possible
@@ -316,8 +316,8 @@ struct bpf_func_state {
 	/* The following fields should be last. See copy_func_state() */
 	int acquired_refs;
 	struct bpf_reference_state *refs;
-	int allocated_stack;
 	struct bpf_stack_state *stack;
+	int allocated_stack;
 };
 
 struct bpf_idx_pair {