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bpf: Fix immediate JMP JEQ/JNE on MIPS32

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An addu instruction was emitted instead of addiu, causing the immediate
value 1 to be interpreted as register $at. This made the comparison
result invalid when the immediate operand was negative. Note that $at
is mapped to BPF_REG_AX, which is used for constant blinding.

Fix the instruction to use the immediate form.

Found with test_bpf on MIPS32r1 emulated by QEMU.

Fixes: eb63cfcd2e ("mips, bpf: Add eBPF JIT for 32-bit MIPS")
Signed-off-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://patch.msgid.link/20260923105158.3514342-1-johan.almbladh@anyfinetworks.com
This commit is contained in:
Johan Almbladh 2026-09-23 12:51:57 +02:00 committed by Alexei Starovoitov
parent 6db1ce73e9
commit db762fd96b
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1 changed files with 1 additions and 1 deletions
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arch/mips/net/bpf_jit_comp32.c
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@ -1111,7 +1111,7 @@ static void emit_jmp_i64(struct jit_context *ctx,
emit(ctx, xor, tmp, lo(dst), tmp);
}
if (imm < 0) { /* Compare sign extension */
emit(ctx, addu, MIPS_R_T9, hi(dst), 1);
emit(ctx, addiu, MIPS_R_T9, hi(dst), 1);
emit(ctx, or, tmp, tmp, MIPS_R_T9);
} else { /* Compare zero extension */
emit(ctx, or, tmp, tmp, hi(dst));