Commit bbcf0f55 authored by Tiezhu Yang's avatar Tiezhu Yang Committed by Daniel Borkmann
Browse files

bpf, mips: No need to use min() to get MAX_TAIL_CALL_CNT 



MAX_TAIL_CALL_CNT is 33, so min(MAX_TAIL_CALL_CNT, 0xffff) is always
MAX_TAIL_CALL_CNT, it is better to use MAX_TAIL_CALL_CNT directly.

At the same time, add BUILD_BUG_ON(MAX_TAIL_CALL_CNT > 0xffff) with a
comment on why the assertion is there.

Suggested-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Suggested-by: default avatarJohan Almbladh <johan.almbladh@anyfinetworks.com>
Signed-off-by: default avatarTiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/1661742309-2320-1-git-send-email-yangtiezhu@loongson.cn
parent aa75622c

arch/mips/net/bpf_jit_comp32.c

+9 −1
Original line number Diff line number Diff line
@@ -1376,12 +1376,20 @@ void build_prologue(struct jit_context *ctx) 
	const u8 *fp = bpf2mips32[BPF_REG_FP];

	int stack, saved, locals, reserved;



	/*

	 * In the unlikely event that the TCC limit is raised to more

	 * than 16 bits, it is clamped to the maximum value allowed for

	 * the generated code (0xffff). It is better fail to compile

	 * instead of degrading gracefully.

	 */

	BUILD_BUG_ON(MAX_TAIL_CALL_CNT > 0xffff);



	/*

	 * The first two instructions initialize TCC in the reserved (for us)

	 * 16-byte area in the parent's stack frame. On a tail call, the

	 * calling function jumps into the prologue after these instructions.

	 */

	emit(ctx, ori, MIPS_R_T9, MIPS_R_ZERO, min(MAX_TAIL_CALL_CNT, 0xffff));

	emit(ctx, ori, MIPS_R_T9, MIPS_R_ZERO, MAX_TAIL_CALL_CNT);

	emit(ctx, sw, MIPS_R_T9, 0, MIPS_R_SP);



	/*

arch/mips/net/bpf_jit_comp64.c

+9 −1
Original line number Diff line number Diff line
@@ -547,12 +547,20 @@ void build_prologue(struct jit_context *ctx) 
	u8 zx = bpf2mips64[JIT_REG_ZX];

	int stack, saved, locals, reserved;



	/*

	 * In the unlikely event that the TCC limit is raised to more

	 * than 16 bits, it is clamped to the maximum value allowed for

	 * the generated code (0xffff). It is better fail to compile

	 * instead of degrading gracefully.

	 */

	BUILD_BUG_ON(MAX_TAIL_CALL_CNT > 0xffff);



	/*

	 * The first instruction initializes the tail call count register.

	 * On a tail call, the calling function jumps into the prologue

	 * after this instruction.

	 */

	emit(ctx, ori, tc, MIPS_R_ZERO, min(MAX_TAIL_CALL_CNT, 0xffff));

	emit(ctx, ori, tc, MIPS_R_ZERO, MAX_TAIL_CALL_CNT);



	/* === Entry-point for tail calls === */