Commit 7ba4f43e authored by Ilya Leoshkevich's avatar Ilya Leoshkevich Committed by Daniel Borkmann
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s390/bpf: Change seen_reg to a mask 



Using a mask instead of an array saves a small amount of memory and
allows marking multiple registers as seen with a simple "or". Another
positive side-effect is that it speeds up verification with jitterbug.

Signed-off-by: default avatarIlya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20240703005047.40915-2-iii@linux.ibm.com
parent bc239eb2

arch/s390/net/bpf_jit_comp.c

+16 −16
Original line number Diff line number Diff line
@@ -35,7 +35,7 @@ 


struct bpf_jit {

	u32 seen;		/* Flags to remember seen eBPF instructions */

	u32 seen_reg[16];	/* Array to remember which registers are used */

	u16 seen_regs;		/* Mask to remember which registers are used */

	u32 *addrs;		/* Array with relative instruction addresses */

	u8 *prg_buf;		/* Start of program */

	int size;		/* Size of program and literal pool */
@@ -120,8 +120,8 @@ static inline void reg_set_seen(struct bpf_jit *jit, u32 b1) 
{

	u32 r1 = reg2hex[b1];



	if (r1 >= 6 && r1 <= 15 && !jit->seen_reg[r1])

		jit->seen_reg[r1] = 1;

	if (r1 >= 6 && r1 <= 15)

		jit->seen_regs |= (1 << r1);

}



#define REG_SET_SEEN(b1)					\
@@ -129,8 +129,6 @@ static inline void reg_set_seen(struct bpf_jit *jit, u32 b1) 
	reg_set_seen(jit, b1);					\

})



#define REG_SEEN(b1) jit->seen_reg[reg2hex[(b1)]]



/*

 * EMIT macros for code generation

 */
@@ -438,12 +436,12 @@ static void restore_regs(struct bpf_jit *jit, u32 rs, u32 re, u32 stack_depth) 
/*

 * Return first seen register (from start)

 */

static int get_start(struct bpf_jit *jit, int start)

static int get_start(u16 seen_regs, int start)

{

	int i;



	for (i = start; i <= 15; i++) {

		if (jit->seen_reg[i])

		if (seen_regs & (1 << i))

			return i;

	}

	return 0;
@@ -452,15 +450,15 @@ static int get_start(struct bpf_jit *jit, int start) 
/*

 * Return last seen register (from start) (gap >= 2)

 */

static int get_end(struct bpf_jit *jit, int start)

static int get_end(u16 seen_regs, int start)

{

	int i;



	for (i = start; i < 15; i++) {

		if (!jit->seen_reg[i] && !jit->seen_reg[i + 1])

		if (!(seen_regs & (3 << i)))

			return i - 1;

	}

	return jit->seen_reg[15] ? 15 : 14;

	return (seen_regs & (1 << 15)) ? 15 : 14;

}



#define REGS_SAVE	1
@@ -469,8 +467,10 @@ static int get_end(struct bpf_jit *jit, int start) 
 * Save and restore clobbered registers (6-15) on stack.

 * We save/restore registers in chunks with gap >= 2 registers.

 */

static void save_restore_regs(struct bpf_jit *jit, int op, u32 stack_depth)

static void save_restore_regs(struct bpf_jit *jit, int op, u32 stack_depth,

			      u16 extra_regs)

{

	u16 seen_regs = jit->seen_regs | extra_regs;

	const int last = 15, save_restore_size = 6;

	int re = 6, rs;
@@ -484,10 +484,10 @@ static void save_restore_regs(struct bpf_jit *jit, int op, u32 stack_depth) 
	}



	do {

		rs = get_start(jit, re);

		rs = get_start(seen_regs, re);

		if (!rs)

			break;

		re = get_end(jit, rs + 1);

		re = get_end(seen_regs, rs + 1);

		if (op == REGS_SAVE)

			save_regs(jit, rs, re);

		else
@@ -573,7 +573,7 @@ static void bpf_jit_prologue(struct bpf_jit *jit, struct bpf_prog *fp, 
	/* Tail calls have to skip above initialization */

	jit->tail_call_start = jit->prg;

	/* Save registers */

	save_restore_regs(jit, REGS_SAVE, stack_depth);

	save_restore_regs(jit, REGS_SAVE, stack_depth, 0);

	/* Setup literal pool */

	if (is_first_pass(jit) || (jit->seen & SEEN_LITERAL)) {

		if (!is_first_pass(jit) &&
@@ -649,7 +649,7 @@ static void bpf_jit_epilogue(struct bpf_jit *jit, u32 stack_depth) 
	/* Load exit code: lgr %r2,%b0 */

	EMIT4(0xb9040000, REG_2, BPF_REG_0);

	/* Restore registers */

	save_restore_regs(jit, REGS_RESTORE, stack_depth);

	save_restore_regs(jit, REGS_RESTORE, stack_depth, 0);

	if (nospec_uses_trampoline()) {

		jit->r14_thunk_ip = jit->prg;

		/* Generate __s390_indirect_jump_r14 thunk */
@@ -1847,7 +1847,7 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, 
		/*

		 * Restore registers before calling function

		 */

		save_restore_regs(jit, REGS_RESTORE, stack_depth);

		save_restore_regs(jit, REGS_RESTORE, stack_depth, 0);



		/*

		 * goto *(prog->bpf_func + tail_call_start);