--- v5
+++ v1
@@ -1,41 +1,123 @@
From: Abhishek Dubey <adubey@linux.ibm.com>
-Back propagation of tailcall count is no longer needed for
-powerpc64 due to use of reference, which updates the tailcall
-count in the tail_call_info field in the frame of the main
-program only.
+In the previous patch, we introduced BPF_PPC_STACK_SAVE
+into the trampoline frame to make its layout consistent
+with a conventional stack frame.
-Back propagation is still required for 32-bit powerpc.
+The trampoline JIT currently uses NVRs R25 and R26 and
+allocates dedicated stack slots to save them. This
+dedicated space can be eliminated by reusing the
+BPF_PPC_STACK_SAVE area instead, reducing overall stack
+footprint.
+
+The BPF_PPC_STACK_SAVE area corresponds to the register
+range R26–R31. By remapping registers in the trampoline
+JIT code (R25 → R26 and R26 → R27), we can spill these
+registers into the existing save area and utilize the stack
+more efficiently.
Signed-off-by: Abhishek Dubey <adubey@linux.ibm.com>
---
- arch/powerpc/net/bpf_jit_comp.c | 13 +++++--------
- 1 file changed, 5 insertions(+), 8 deletions(-)
+ arch/powerpc/net/bpf_jit_comp.c | 27 +++++++++++----------------
+ 1 file changed, 11 insertions(+), 16 deletions(-)
diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
-index 4b18daed054a..f8769d785123 100644
+index 4aaa0a287a45..b09d294084d4 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
-@@ -659,14 +659,11 @@ static void bpf_trampoline_setup_tail_call_info(u32 *image, struct codegen_conte
- static void bpf_trampoline_restore_tail_call_cnt(u32 *image, struct codegen_context *ctx,
- int func_frame_offset, int r4_off)
- {
-- if (IS_ENABLED(CONFIG_PPC64)) {
-- /* See bpf_jit_stack_tailcallcnt() */
-- int tailcallcnt_offset = BPF_PPC_TAILCALL;
+@@ -512,7 +512,7 @@ static int invoke_bpf_prog(u32 *image, u32 *ro_image, struct codegen_context *ct
+
+ /* __bpf_prog_enter(p, &bpf_tramp_run_ctx) */
+ PPC_LI_ADDR(_R3, p);
+- EMIT(PPC_RAW_MR(_R25, _R3));
++ EMIT(PPC_RAW_MR(_R26, _R3));
+ EMIT(PPC_RAW_ADDI(_R4, _R1, run_ctx_off));
+ ret = bpf_jit_emit_func_call_rel(image, ro_image, ctx,
+ (unsigned long)bpf_trampoline_enter(p));
+@@ -520,7 +520,7 @@ static int invoke_bpf_prog(u32 *image, u32 *ro_image, struct codegen_context *ct
+ return ret;
+
+ /* Remember prog start time returned by __bpf_prog_enter */
+- EMIT(PPC_RAW_MR(_R26, _R3));
++ EMIT(PPC_RAW_MR(_R27, _R3));
+
+ /*
+ * if (__bpf_prog_enter(p) == 0)
+@@ -543,7 +543,7 @@ static int invoke_bpf_prog(u32 *image, u32 *ro_image, struct codegen_context *ct
+ image[ctx->idx] = ppc_inst_val(branch_insn);
+ ctx->idx++;
+ } else {
+- EMIT(PPC_RAW_LL(_R12, _R25, offsetof(struct bpf_prog, bpf_func)));
++ EMIT(PPC_RAW_LL(_R12, _R26, offsetof(struct bpf_prog, bpf_func)));
+ EMIT(PPC_RAW_MTCTR(_R12));
+ EMIT(PPC_RAW_BCTRL());
+ }
+@@ -560,8 +560,8 @@ static int invoke_bpf_prog(u32 *image, u32 *ro_image, struct codegen_context *ct
+ }
+
+ /* __bpf_prog_exit(p, start_time, &bpf_tramp_run_ctx) */
+- EMIT(PPC_RAW_MR(_R3, _R25));
+- EMIT(PPC_RAW_MR(_R4, _R26));
++ EMIT(PPC_RAW_MR(_R3, _R26));
++ EMIT(PPC_RAW_MR(_R4, _R27));
+ EMIT(PPC_RAW_ADDI(_R5, _R1, run_ctx_off));
+ ret = bpf_jit_emit_func_call_rel(image, ro_image, ctx,
+ (unsigned long)bpf_trampoline_exit(p));
+@@ -748,12 +748,10 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
+ * [ r0 save (32-bit) ] |
+ * dummy frame for unwind [ back chain 1 ] --
+ * [ padding ] align stack frame
+- * [ r26..r31 ] nvr save : BPF_PPC_STACK_SAVE
++ * nvr_off [ r26..r31 ] nvr save : BPF_PPC_STACK_SAVE
+ * [ tail_call_info ] non optional - 64-bit powerpc
+ * r4_off [ r4 (tailcallcnt) ] optional - 32-bit powerpc
+ * alt_lr_off [ real lr (ool stub)] optional - actual lr
+- * [ r26 ]
+- * nvr_off [ r25 ] nvr save area
+ * retval_off [ return value ]
+ * [ reg argN ]
+ * [ ... ]
+@@ -811,10 +809,6 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
+ if (save_ret)
+ bpf_frame_size += SZL;
+
+- /* Room for nvr save area */
+- nvr_off = bpf_frame_size;
+- bpf_frame_size += 2 * SZL;
-
-- EMIT(PPC_RAW_LL(_R3, _R1, -tailcallcnt_offset));
-- EMIT(PPC_RAW_STL(_R3, _R1, func_frame_offset - tailcallcnt_offset));
-- } else {
-- /* See bpf_jit_stack_offsetof() and BPF_PPC_TC */
-+ if (IS_ENABLED(CONFIG_PPC32)) {
-+ /*
-+ * Restore tailcall for 32-bit powerpc
-+ * See bpf_jit_stack_offsetof() and BPF_PPC_TC
-+ */
- EMIT(PPC_RAW_STL(_R4, _R1, r4_off));
- }
- }
+ /* Optional save area for actual LR in case of ool ftrace */
+ if (IS_ENABLED(CONFIG_PPC_FTRACE_OUT_OF_LINE)) {
+ alt_lr_off = bpf_frame_size;
+@@ -834,6 +828,7 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
+ bpf_frame_size += SZL;
+
+ /* Room for nvr save area */
++ nvr_off = bpf_frame_size;
+ bpf_frame_size += BPF_PPC_STACK_SAVE;
+
+ /* Padding to align stack frame, if any */
+@@ -897,8 +892,8 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
+ EMIT(PPC_RAW_STL(_R3, _R1, nregs_off));
+
+ /* Save nv regs */
+- EMIT(PPC_RAW_STL(_R25, _R1, nvr_off));
+- EMIT(PPC_RAW_STL(_R26, _R1, nvr_off + SZL));
++ EMIT(PPC_RAW_STL(_R26, _R1, nvr_off));
++ EMIT(PPC_RAW_STL(_R27, _R1, nvr_off + SZL));
+
+ if (flags & BPF_TRAMP_F_CALL_ORIG) {
+ PPC_LI_ADDR(_R3, (unsigned long)im);
+@@ -999,8 +994,8 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
+ EMIT(PPC_RAW_LL(_R3, _R1, retval_off));
+
+ /* Restore nv regs */
+- EMIT(PPC_RAW_LL(_R26, _R1, nvr_off + SZL));
+- EMIT(PPC_RAW_LL(_R25, _R1, nvr_off));
++ EMIT(PPC_RAW_LL(_R27, _R1, nvr_off + SZL));
++ EMIT(PPC_RAW_LL(_R26, _R1, nvr_off));
+
+ /* Epilogue */
+ if (IS_ENABLED(CONFIG_PPC64_ELF_ABI_V2) && !IS_ENABLED(CONFIG_PPC_KERNEL_PCREL))
--
2.48.1