linux-kernel - [PATCH bpf 5/7] bpf/powerpc64: use define for max regs count used for arguments

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Message-Id: <20250613-deny_trampoline_structs_on_stack-v1-5-5be9211768c3@bootlin.com>
Date: Fri, 13 Jun 2025 09:37:14 +0200
From: Alexis Lothoré (eBPF Foundation) <alexis.lothore@...tlin.com>
To: Alexei Starovoitov <ast@...nel.org>, 
 Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, 
 Martin KaFai Lau <martin.lau@...ux.dev>, 
 Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
 Yonghong Song <yonghong.song@...ux.dev>, 
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, 
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
 Jiri Olsa <jolsa@...nel.org>, "David S. Miller" <davem@...emloft.net>, 
 David Ahern <dsahern@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, 
 Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
 Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
 "H. Peter Anvin" <hpa@...or.com>, Menglong Dong <imagedong@...cent.com>, 
 Björn Töpel <bjorn@...nel.org>, 
 Pu Lehui <pulehui@...wei.com>, Puranjay Mohan <puranjay@...nel.org>, 
 Paul Walmsley <paul.walmsley@...ive.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
 Alexandre Ghiti <alex@...ti.fr>, Ilya Leoshkevich <iii@...ux.ibm.com>, 
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 Christophe Leroy <christophe.leroy@...roup.eu>, 
 Naveen N Rao <naveen@...nel.org>, Madhavan Srinivasan <maddy@...ux.ibm.com>, 
 Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>, 
 Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>, 
 Maxime Coquelin <mcoquelin.stm32@...il.com>, 
 Alexandre Torgue <alexandre.torgue@...s.st.com>
Cc: ebpf@...uxfoundation.org, 
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
 Bastien Curutchet <bastien.curutchet@...tlin.com>, netdev@...r.kernel.org, 
 bpf@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Björn Töpel <bjorn@...osinc.com>, 
 linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org, 
 linuxppc-dev@...ts.ozlabs.org, linux-kselftest@...r.kernel.org, 
 linux-stm32@...md-mailman.stormreply.com, 
 linux-arm-kernel@...ts.infradead.org, 
 Alexis Lothoré (eBPF Foundation) <alexis.lothore@...tlin.com>
Subject: [PATCH bpf 5/7] bpf/powerpc64: use define for max regs count used
 for arguments

powerpc allows using up to 8 registers to pass arguments between function
calls. This value is hardcoded in multiple places, use a define for this
value.

Signed-off-by: Alexis Lothoré (eBPF Foundation) <alexis.lothore@...tlin.com>
---
 arch/powerpc/net/bpf_jit_comp.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index c0684733e9d6ac79b4cf653bf1b9ad40eb3e1aca..d313920a42c2310c6b5deab6d82e13af49c8ecb1 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -22,6 +22,8 @@

 #include "bpf_jit.h"

+#define MAX_REGS_FOR_ARGS	8
+
 /* These offsets are from bpf prog end and stay the same across progs */
 static int bpf_jit_ool_stub, bpf_jit_long_branch_stub;

@@ -613,7 +615,7 @@ static void bpf_trampoline_save_args(u32 *image, struct codegen_context *ctx, in
 	param_save_area_offset += STACK_FRAME_MIN_SIZE; /* param save area is past frame header */

 	for (int i = 0; i < nr_regs; i++) {
-		if (i < 8) {
+		if (i < MAX_REGS_FOR_ARGS) {
 			EMIT(PPC_RAW_STL(_R3 + i, _R1, regs_off + i * SZL));
 		} else {
 			EMIT(PPC_RAW_LL(_R3, _R1, param_save_area_offset + i * SZL));
@@ -626,7 +628,7 @@ static void bpf_trampoline_save_args(u32 *image, struct codegen_context *ctx, in
 static void bpf_trampoline_restore_args_regs(u32 *image, struct codegen_context *ctx,
 					     int nr_regs, int regs_off)
 {
-	for (int i = 0; i < nr_regs && i < 8; i++)
+	for (int i = 0; i < nr_regs && i < MAX_REGS_FOR_ARGS; i++)
 		EMIT(PPC_RAW_LL(_R3 + i, _R1, regs_off + i * SZL));
 }

@@ -725,7 +727,9 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
 	 *
 	 * Reserve space for at least 8 registers for now. This can be optimized later.
 	 */
-	bpf_frame_size += (nr_regs > 8 ? nr_regs : 8) * SZL;
+	bpf_frame_size +=
+		(nr_regs > MAX_REGS_FOR_ARGS ? nr_regs : MAX_REGS_FOR_ARGS) *
+		SZL;

 	/* Room for struct bpf_tramp_run_ctx */
 	run_ctx_off = bpf_frame_size;

-- 
2.49.0