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[213.115.136.2]) by smtp.gmail.com with ESMTPSA id gb24sm71772ejc.53.2021.09.07.15.24.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 Sep 2021 15:24:01 -0700 (PDT) From: Johan Almbladh To: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org Cc: kafai@fb.com, songliubraving@fb.com, yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org, iii@linux.ibm.com, netdev@vger.kernel.org, bpf@vger.kernel.org, Johan Almbladh Subject: [PATCH bpf-next v2 13/13] bpf/tests: Add tail call limit test with external function call Date: Wed, 8 Sep 2021 00:23:39 +0200 Message-Id: <20210907222339.4130924-14-johan.almbladh@anyfinetworks.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210907222339.4130924-1-johan.almbladh@anyfinetworks.com> References: <20210907222339.4130924-1-johan.almbladh@anyfinetworks.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net This patch adds a tail call limit test where the program also emits a BPF_CALL to an external function prior to the tail call. Mainly testing that JITed programs preserve its internal register state, for example tail call count, across such external calls. Signed-off-by: Johan Almbladh --- lib/test_bpf.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 48 insertions(+), 3 deletions(-) diff --git a/lib/test_bpf.c b/lib/test_bpf.c index 7475abfd2186..6e45b4da9841 100644 --- a/lib/test_bpf.c +++ b/lib/test_bpf.c @@ -12259,6 +12259,20 @@ static struct tail_call_test tail_call_tests[] = { }, .result = MAX_TAIL_CALL_CNT + 1, }, + { + "Tail call count preserved across function calls", + .insns = { + BPF_ALU64_IMM(BPF_ADD, R1, 1), + BPF_STX_MEM(BPF_DW, R10, R1, -8), + BPF_CALL_REL(0), + BPF_LDX_MEM(BPF_DW, R1, R10, -8), + BPF_ALU32_REG(BPF_MOV, R0, R1), + TAIL_CALL(0), + BPF_EXIT_INSN(), + }, + .stack_depth = 8, + .result = MAX_TAIL_CALL_CNT + 1, + }, { "Tail call error path, NULL target", .insns = { @@ -12281,6 +12295,29 @@ static struct tail_call_test tail_call_tests[] = { }, }; +/* + * A test function to be called from a BPF program, clobbering a lot of + * CPU registers in the process. A JITed BPF program calling this function + * must save and restore any caller-saved registers it uses for internal + * state, for example the current tail call count. + */ +BPF_CALL_1(test_bpf_func, u64, arg) +{ + char buf[64]; + long a = 0; + long b = 1; + long c = 2; + long d = 3; + long e = 4; + long f = 5; + long g = 6; + long h = 7; + + return snprintf(buf, sizeof(buf), + "%ld %lu %lx %ld %lu %lx %ld %lu %x", + a, b, c, d, e, f, g, h, (int)arg); +} + static void __init destroy_tail_call_tests(struct bpf_array *progs) { int i; @@ -12334,16 +12371,17 @@ static __init int prepare_tail_call_tests(struct bpf_array **pprogs) for (i = 0; i < len; i++) { struct bpf_insn *insn = &fp->insnsi[i]; - if (insn->imm != TAIL_CALL_MARKER) - continue; - switch (insn->code) { case BPF_LD | BPF_DW | BPF_IMM: + if (insn->imm != TAIL_CALL_MARKER) + break; insn[0].imm = (u32)(long)progs; insn[1].imm = ((u64)(long)progs) >> 32; break; case BPF_ALU | BPF_MOV | BPF_K: + if (insn->imm != TAIL_CALL_MARKER) + break; if (insn->off == TAIL_CALL_NULL) insn->imm = ntests; else if (insn->off == TAIL_CALL_INVALID) @@ -12351,6 +12389,13 @@ static __init int prepare_tail_call_tests(struct bpf_array **pprogs) else insn->imm = which + insn->off; insn->off = 0; + break; + + case BPF_JMP | BPF_CALL: + if (insn->src_reg != BPF_PSEUDO_CALL) + break; + *insn = BPF_EMIT_CALL(test_bpf_func); + break; } }