[PATCH bpf-next v6 1/3] riscv, bpf: Add 12-argument support for RV64 bpf trampoline

Pu Lehui
2024-07-02T12:18:08Z

From: Pu Lehui <pulehui@huawei.com>

This patch adds 12 function arguments support for riscv64 bpf
trampoline. The current bpf trampoline supports <= sizeof(u64) bytes
scalar arguments [0] and <= 16 bytes struct arguments [1]. Therefore, we
focus on the situation where scalars are at most XLEN bits and
aggregates whose total size does not exceed 2×XLEN bits in the riscv
calling convention [2].

Link: https://elixir.bootlin.com/linux/v6.8/source/kernel/bpf/btf.c#L6184 [0]
Link: https://elixir.bootlin.com/linux/v6.8/source/kernel/bpf/btf.c#L6769 [1]
Link: https://github.com/riscv-non-isa/riscv-elf-psabi-doc/releases/download/draft-20230929-e5c800e661a53efe3c2678d71a306323b60eb13b/riscv-abi.pdf [2]
Signed-off-by: Pu Lehui <pulehui@huawei.com>
Acked-by: Björn Töpel <bjorn@kernel.org>
Reviewed-by: Björn Töpel <bjorn@rivosinc.com>
---
arch/riscv/net/bpf_jit_comp64.c | 66 +++++++++++++++++++++++----------
1 file changed, 47 insertions(+), 19 deletions(-)

diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
index 351e1484205e..685c7389ae7e 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -15,6 +15,7 @@
#include <asm/percpu.h>
#include "bpf_jit.h"

+#define RV_MAX_REG_ARGS 8
#define RV_FENTRY_NINSNS 2
/* imm that allows emit_imm to emit max count insns */
#define RV_MAX_COUNT_IMM 0x7FFF7FF7FF7FF7FF
@@ -692,26 +693,45 @@ int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type poke_type,
return ret;
}

-static void store_args(int nregs, int args_off, struct rv_jit_context *ctx)
+static void store_args(int nr_arg_slots, int args_off, struct rv_jit_context *ctx)
{
int i;

- for (i = 0; i < nregs; i++) {
- emit_sd(RV_REG_FP, -args_off, RV_REG_A0 + i, ctx);
+ for (i = 0; i < nr_arg_slots; i++) {
+ if (i < RV_MAX_REG_ARGS) {
+ emit_sd(RV_REG_FP, -args_off, RV_REG_A0 + i, ctx);
+ } else {
+ /* skip slots for T0 and FP of traced function */
+ emit_ld(RV_REG_T1, 16 + (i - RV_MAX_REG_ARGS) * 8, RV_REG_FP, ctx);
+ emit_sd(RV_REG_FP, -args_off, RV_REG_T1, ctx);
+ }
args_off -= 8;
}
}

-static void restore_args(int nregs, int args_off, struct rv_jit_context *ctx)
+static void restore_args(int nr_reg_args, int args_off, struct rv_jit_context *ctx)
{
int i;

- for (i = 0; i < nregs; i++) {
+ for (i = 0; i < nr_reg_args; i++) {
emit_ld(RV_REG_A0 + i, -args_off, RV_REG_FP, ctx);
args_off -= 8;
}
}

+static void restore_stack_args(int nr_stack_args, int args_off, int stk_arg_off,
+ struct rv_jit_context *ctx)
+{
+ int i;
+
+ for (i = 0; i < nr_stack_args; i++) {
+ emit_ld(RV_REG_T1, -(args_off - RV_MAX_REG_ARGS * 8), RV_REG_FP, ctx);
+ emit_sd(RV_REG_FP, -stk_arg_off, RV_REG_T1, ctx);
+ args_off -= 8;
+ stk_arg_off -= 8;
+ }
+}
+
static int invoke_bpf_prog(struct bpf_tramp_link *l, int args_off, int retval_off,
int run_ctx_off, bool save_ret, struct rv_jit_context *ctx)
{
@@ -784,8 +804,8 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
{
int i, ret, offset;
int *branches_off = NULL;
- int stack_size = 0, nregs = m->nr_args;
- int retval_off, args_off, nregs_off, ip_off, run_ctx_off, sreg_off;
+ int stack_size = 0, nr_arg_slots = 0;
+ int retval_off, args_off, nregs_off, ip_off, run_ctx_off, sreg_off, stk_arg_off;
struct bpf_tramp_links *fentry = &tlinks[BPF_TRAMP_FENTRY];
struct bpf_tramp_links *fexit = &tlinks[BPF_TRAMP_FEXIT];
struct bpf_tramp_links *fmod_ret = &tlinks[BPF_TRAMP_MODIFY_RETURN];
@@ -831,20 +851,21 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
* FP - sreg_off [ callee saved reg ]
*
* [ pads ] pads for 16 bytes alignment
+ *
+ * [ stack_argN ]
+ * [ ... ]
+ * FP - stk_arg_off [ stack_arg1 ] BPF_TRAMP_F_CALL_ORIG
*/

if (flags & (BPF_TRAMP_F_ORIG_STACK | BPF_TRAMP_F_SHARE_IPMODIFY))
return -ENOTSUPP;

- /* extra regiters for struct arguments */
- for (i = 0; i < m->nr_args; i++)
- if (m->arg_flags[i] & BTF_FMODEL_STRUCT_ARG)
- nregs += round_up(m->arg_size[i], 8) / 8 - 1;
-
- /* 8 arguments passed by registers */
- if (nregs > 8)
+ if (m->nr_args > MAX_BPF_FUNC_ARGS)
return -ENOTSUPP;

+ for (i = 0; i < m->nr_args; i++)
+ nr_arg_slots += round_up(m->arg_size[i], 8) / 8;
+
/* room of trampoline frame to store return address and frame pointer */
stack_size += 16;

@@ -854,7 +875,7 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
retval_off = stack_size;
}

- stack_size += nregs * 8;
+ stack_size += nr_arg_slots * 8;
args_off = stack_size;

stack_size += 8;
@@ -871,8 +892,14 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
stack_size += 8;
sreg_off = stack_size;

+ if (nr_arg_slots - RV_MAX_REG_ARGS > 0)
+ stack_size += (nr_arg_slots - RV_MAX_REG_ARGS) * 8;
+
stack_size = round_up(stack_size, STACK_ALIGN);

+ /* room for args on stack must be at the top of stack */
+ stk_arg_off = stack_size;
+
if (!is_struct_ops) {
/* For the trampoline called from function entry,
* the frame of traced function and the frame of
@@ -908,10 +935,10 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
emit_sd(RV_REG_FP, -ip_off, RV_REG_T1, ctx);
}

- emit_li(RV_REG_T1, nregs, ctx);
+ emit_li(RV_REG_T1, nr_arg_slots, ctx);
emit_sd(RV_REG_FP, -nregs_off, RV_REG_T1, ctx);

- store_args(nregs, args_off, ctx);
+ store_args(nr_arg_slots, args_off, ctx);

/* skip to actual body of traced function */
if (flags & BPF_TRAMP_F_SKIP_FRAME)
@@ -951,7 +978,8 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
}

if (flags & BPF_TRAMP_F_CALL_ORIG) {
- restore_args(nregs, args_off, ctx);
+ restore_args(min_t(int, nr_arg_slots, RV_MAX_REG_ARGS), args_off, ctx);
+ restore_stack_args(nr_arg_slots - RV_MAX_REG_ARGS, args_off, stk_arg_off, ctx);
ret = emit_call((const u64)orig_call, true, ctx);
if (ret)
goto out;
@@ -986,7 +1014,7 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
}

if (flags & BPF_TRAMP_F_RESTORE_REGS)
- restore_args(nregs, args_off, ctx);
+ restore_args(min_t(int, nr_arg_slots, RV_MAX_REG_ARGS), args_off, ctx);

if (save_ret) {
emit_ld(RV_REG_A0, -retval_off, RV_REG_FP, ctx);
--
2.34.1