From bbcf0f55e57841e532ab395596db9197e8d53e8d Mon Sep 17 00:00:00 2001 From: Tiezhu Yang Date: Mon, 29 Aug 2022 11:05:09 +0800 Subject: 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: Daniel Borkmann Suggested-by: Johan Almbladh Signed-off-by: Tiezhu Yang Signed-off-by: Daniel Borkmann Link: https://lore.kernel.org/bpf/1661742309-2320-1-git-send-email-yangtiezhu@loongson.cn --- arch/mips/net/bpf_jit_comp32.c | 10 +++++++++- arch/mips/net/bpf_jit_comp64.c | 10 +++++++++- 2 files changed, 18 insertions(+), 2 deletions(-) (limited to 'arch/mips') diff --git a/arch/mips/net/bpf_jit_comp32.c b/arch/mips/net/bpf_jit_comp32.c index 83c975d5cca2..ace5db3fbd17 100644 --- a/arch/mips/net/bpf_jit_comp32.c +++ b/arch/mips/net/bpf_jit_comp32.c @@ -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); /* diff --git a/arch/mips/net/bpf_jit_comp64.c b/arch/mips/net/bpf_jit_comp64.c index 6475828ffb36..0e7c1bdcf914 100644 --- a/arch/mips/net/bpf_jit_comp64.c +++ b/arch/mips/net/bpf_jit_comp64.c @@ -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 === */ -- cgit v1.2.3