Unverified Commit 9b6584e3 authored by Paul Burton's avatar Paul Burton
Browse files

MIPS: jump_label: Use compact branches for >= r6 



MIPSr6 introduced compact branches which have no delay slots. Make use
of them for jump labels in order to avoid the need for a nop to fill the
branch or jump delay slot, saving 4 bytes of code for each static branch.

Signed-off-by: default avatarPaul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
parent c838b580

arch/mips/include/asm/jump_label.h

+9 −3
Original line number Diff line number Diff line
@@ -11,6 +11,7 @@ 
#ifndef __ASSEMBLY__



#include <linux/types.h>

#include <asm/isa-rev.h>



#define JUMP_LABEL_NOP_SIZE 4
@@ -22,8 +23,13 @@ 


#ifdef CONFIG_CPU_MICROMIPS

# define B_INSN "b32"

# define J_INSN "j32"

#elif MIPS_ISA_REV >= 6

# define B_INSN "bc"

# define J_INSN "bc"

#else

# define B_INSN "b"

# define J_INSN "j"

#endif



static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
@@ -42,7 +48,7 @@ l_yes: 


static __always_inline bool arch_static_branch_jump(struct static_key *key, bool branch)

{

	asm_volatile_goto("1:\tj %l[l_yes]\n\t"

	asm_volatile_goto("1:\t" J_INSN " %l[l_yes]\n\t"

		".pushsection __jump_table,  \"aw\"\n\t"

		WORD_INSN " 1b, %l[l_yes], %0\n\t"

		".popsection\n\t"

arch/mips/kernel/jump_label.c

+25 −5
Original line number Diff line number Diff line
@@ -40,18 +40,38 @@ void arch_jump_label_transform(struct jump_entry *e, 
{

	union mips_instruction *insn_p;

	union mips_instruction insn;

	long offset;



	insn_p = (union mips_instruction *)msk_isa16_mode(e->code);



	/* Jump only works within an aligned region its delay slot is in. */

	BUG_ON((e->target & ~J_RANGE_MASK) != ((e->code + 4) & ~J_RANGE_MASK));



	/* Target must have the right alignment and ISA must be preserved. */

	BUG_ON((e->target & J_ALIGN_MASK) != J_ISA_BIT);



	if (type == JUMP_LABEL_JMP) {

		if (!IS_ENABLED(CONFIG_CPU_MICROMIPS) && MIPS_ISA_REV >= 6) {

			offset = e->target - ((unsigned long)insn_p + 4);

			offset >>= 2;



			/*

			 * The branch offset must fit in the instruction's 26

			 * bit field.

			 */

			WARN_ON((offset >= BIT(25)) ||

				(offset < -(long)BIT(25)));



			insn.j_format.opcode = bc6_op;

			insn.j_format.target = offset;

		} else {

			/*

			 * Jump only works within an aligned region its delay

			 * slot is in.

			 */

			WARN_ON((e->target & ~J_RANGE_MASK) !=

				((e->code + 4) & ~J_RANGE_MASK));



			insn.j_format.opcode = J_ISA_BIT ? mm_j32_op : j_op;

			insn.j_format.target = e->target >> J_RANGE_SHIFT;

		}

	} else {

		insn.word = 0; /* nop */

	}

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