From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
linuxppc-dev@lists.ozlabs.org, bpf@vger.kernel.org
Subject: Re: [PATCH] powerpc/bpf: Use bctrl for making function calls
Date: Wed, 9 Jun 2021 11:42:47 +0200 [thread overview]
Message-ID: <4c371bd1-1fcf-54c1-d0a2-836d40887893@csgroup.eu> (raw)
In-Reply-To: <20210609090024.1446800-1-naveen.n.rao@linux.vnet.ibm.com>
Le 09/06/2021 à 11:00, Naveen N. Rao a écrit :
> blrl corrupts the link stack. Instead use bctrl when making function
> calls from BPF programs.
What's the link stack ? Is it the PPC64 branch predictor stack ?
>
> Reported-by: Anton Blanchard <anton@ozlabs.org>
> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
> ---
> arch/powerpc/include/asm/ppc-opcode.h | 1 +
> arch/powerpc/net/bpf_jit_comp32.c | 4 ++--
> arch/powerpc/net/bpf_jit_comp64.c | 12 ++++++------
> 3 files changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/ppc-opcode.h b/arch/powerpc/include/asm/ppc-opcode.h
> index ac41776661e963..1abacb8417d562 100644
> --- a/arch/powerpc/include/asm/ppc-opcode.h
> +++ b/arch/powerpc/include/asm/ppc-opcode.h
> @@ -451,6 +451,7 @@
> #define PPC_RAW_MTLR(r) (0x7c0803a6 | ___PPC_RT(r))
> #define PPC_RAW_MFLR(t) (PPC_INST_MFLR | ___PPC_RT(t))
> #define PPC_RAW_BCTR() (PPC_INST_BCTR)
> +#define PPC_RAW_BCTRL() (PPC_INST_BCTRL)
Can you use the numeric value instead of the PPC_INST_BCTRL, to avoid conflict with
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/4ca2bfdca2f47a293d05f61eb3c4e487ee170f1f.1621506159.git.christophe.leroy@csgroup.eu/
> #define PPC_RAW_MTCTR(r) (PPC_INST_MTCTR | ___PPC_RT(r))
> #define PPC_RAW_ADDI(d, a, i) (PPC_INST_ADDI | ___PPC_RT(d) | ___PPC_RA(a) | IMM_L(i))
> #define PPC_RAW_LI(r, i) PPC_RAW_ADDI(r, 0, i)
> diff --git a/arch/powerpc/net/bpf_jit_comp32.c b/arch/powerpc/net/bpf_jit_comp32.c
> index bbb16099e8c7fa..40ab50bea61c02 100644
> --- a/arch/powerpc/net/bpf_jit_comp32.c
> +++ b/arch/powerpc/net/bpf_jit_comp32.c
> @@ -195,8 +195,8 @@ void bpf_jit_emit_func_call_rel(u32 *image, struct codegen_context *ctx, u64 fun
> /* Load function address into r0 */
> EMIT(PPC_RAW_LIS(__REG_R0, IMM_H(func)));
> EMIT(PPC_RAW_ORI(__REG_R0, __REG_R0, IMM_L(func)));
> - EMIT(PPC_RAW_MTLR(__REG_R0));
> - EMIT(PPC_RAW_BLRL());
> + EMIT(PPC_RAW_MTCTR(__REG_R0));
> + EMIT(PPC_RAW_BCTRL());
> }
> }
>
> diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
> index 57a8c1153851a0..ae9a6532be6ad4 100644
> --- a/arch/powerpc/net/bpf_jit_comp64.c
> +++ b/arch/powerpc/net/bpf_jit_comp64.c
> @@ -153,8 +153,8 @@ static void bpf_jit_emit_func_call_hlp(u32 *image, struct codegen_context *ctx,
> PPC_LI64(b2p[TMP_REG_2], func);
> /* Load actual entry point from function descriptor */
> PPC_BPF_LL(b2p[TMP_REG_1], b2p[TMP_REG_2], 0);
> - /* ... and move it to LR */
> - EMIT(PPC_RAW_MTLR(b2p[TMP_REG_1]));
> + /* ... and move it to CTR */
> + EMIT(PPC_RAW_MTCTR(b2p[TMP_REG_1]));
> /*
> * Load TOC from function descriptor at offset 8.
> * We can clobber r2 since we get called through a
> @@ -165,9 +165,9 @@ static void bpf_jit_emit_func_call_hlp(u32 *image, struct codegen_context *ctx,
> #else
> /* We can clobber r12 */
> PPC_FUNC_ADDR(12, func);
> - EMIT(PPC_RAW_MTLR(12));
> + EMIT(PPC_RAW_MTCTR(12));
> #endif
> - EMIT(PPC_RAW_BLRL());
> + EMIT(PPC_RAW_BCTRL());
> }
>
> void bpf_jit_emit_func_call_rel(u32 *image, struct codegen_context *ctx, u64 func)
> @@ -202,8 +202,8 @@ void bpf_jit_emit_func_call_rel(u32 *image, struct codegen_context *ctx, u64 fun
> PPC_BPF_LL(12, 12, 0);
> #endif
>
> - EMIT(PPC_RAW_MTLR(12));
> - EMIT(PPC_RAW_BLRL());
> + EMIT(PPC_RAW_MTCTR(12));
> + EMIT(PPC_RAW_BCTRL());
> }
>
> static void bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 out)
>
> base-commit: 112f47a1484ddca610b70cbe4a99f0d0f1701daf
>
next prev parent reply other threads:[~2021-06-09 9:43 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-09 9:00 [PATCH] powerpc/bpf: Use bctrl for making function calls Naveen N. Rao
2021-06-09 9:42 ` Christophe Leroy [this message]
2021-06-09 13:11 ` Naveen N. Rao
2021-06-26 10:37 ` Michael Ellerman
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