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

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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 <daniel@iogearbox.net>
Suggested-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/1661742309-2320-1-git-send-email-yangtiezhu@loongson.cn
This commit is contained in:
Tiezhu Yang 2022-08-29 11:05:09 +08:00 committed by Daniel Borkmann
parent aa75622c3b
commit bbcf0f55e5
2 changed files with 18 additions and 2 deletions
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10
arch/mips/net/bpf_jit_comp32.c
View File

@ -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);
/*

10
arch/mips/net/bpf_jit_comp64.c
View File

@ -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 === */