[PATCH v2 5/6] powerpc64/bpf: Support exceptions

adubey
2026-01-14T11:46:48Z

From: Abhishek Dubey <adubey@linux.ibm.com>

The modified prologue/epilogue generation code now
enables exception-callback to use the stack frame of
the program marked as exception boundary, where callee
saved registers are stored.

As per ppc64 ABIv2 documentation[1], r14-r31 are callee
saved registers. BPF programs on ppc64 already saves
r26-r31 registers. Saving the remaining set of callee
saved registers(r14-r25) is handled in the next patch.

[1] https://ftp.rtems.org/pub/rtems/people/sebh/ABI64BitOpenPOWERv1.1_16July2015_pub.pdf

Signed-off-by: Abhishek Dubey <adubey@linux.ibm.com>
---
arch/powerpc/net/bpf_jit.h | 2 ++
arch/powerpc/net/bpf_jit_comp.c | 7 ++++
arch/powerpc/net/bpf_jit_comp64.c | 53 +++++++++++++++++++++----------
3 files changed, 45 insertions(+), 17 deletions(-)

diff --git a/arch/powerpc/net/bpf_jit.h b/arch/powerpc/net/bpf_jit.h
index 5d735bc5e6bd..fb548ae5d143 100644
--- a/arch/powerpc/net/bpf_jit.h
+++ b/arch/powerpc/net/bpf_jit.h
@@ -179,6 +179,8 @@ struct codegen_context {
u64 arena_vm_start;
u64 user_vm_start;
bool is_subprog;
+ bool exception_boundary;
+ bool exception_cb;
};

#define bpf_to_ppc(r) (ctx->b2p[r])
diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index e3088cf089d1..26991940d36e 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -207,6 +207,8 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
cgctx.arena_vm_start = bpf_arena_get_kern_vm_start(fp->aux->arena);
cgctx.user_vm_start = bpf_arena_get_user_vm_start(fp->aux->arena);
cgctx.is_subprog = bpf_is_subprog(fp);
+ cgctx.exception_boundary = fp->aux->exception_boundary;
+ cgctx.exception_cb = fp->aux->exception_cb;

/* Scouting faux-generate pass 0 */
if (bpf_jit_build_body(fp, NULL, NULL, &cgctx, addrs, 0, false)) {
@@ -436,6 +438,11 @@ void bpf_jit_free(struct bpf_prog *fp)
bpf_prog_unlock_free(fp);
}

+bool bpf_jit_supports_exceptions(void)
+{
+ return IS_ENABLED(CONFIG_PPC64);
+}
+
bool bpf_jit_supports_subprog_tailcalls(void)
{
return IS_ENABLED(CONFIG_PPC64);
diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index ec58395f74f7..a6083dd9786c 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -89,7 +89,9 @@ static inline bool bpf_has_stack_frame(struct codegen_context *ctx)
* - the bpf program uses its stack area
* The latter condition is deduced from the usage of BPF_REG_FP
*/
- return ctx->seen & SEEN_FUNC || bpf_is_seen_register(ctx, bpf_to_ppc(BPF_REG_FP));
+ return ctx->seen & SEEN_FUNC ||
+ bpf_is_seen_register(ctx, bpf_to_ppc(BPF_REG_FP)) ||
+ ctx->exception_cb;
}

/*
@@ -190,23 +192,32 @@ void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx)
EMIT(PPC_RAW_STDU(_R1, _R1, -(BPF_PPC_STACKFRAME + ctx->stack_size)));
}

- /*
- * Back up non-volatile regs -- BPF registers 6-10
- * If we haven't created our own stack frame, we save these
- * in the protected zone below the previous stack frame
- */
- for (i = BPF_REG_6; i <= BPF_REG_10; i++)
- if (bpf_is_seen_register(ctx, bpf_to_ppc(i)))
- EMIT(PPC_RAW_STD(bpf_to_ppc(i), _R1, bpf_jit_stack_offsetof(ctx, bpf_to_ppc(i))));
+ if (!ctx->exception_cb) {
+ /*
+ * Back up non-volatile regs -- BPF registers 6-10
+ * If we haven't created our own stack frame, we save these
+ * in the protected zone below the previous stack frame
+ */
+ for (i = BPF_REG_6; i <= BPF_REG_10; i++)
+ if (ctx->exception_boundary || bpf_is_seen_register(ctx, bpf_to_ppc(i)))
+ EMIT(PPC_RAW_STD(bpf_to_ppc(i), _R1,
+ bpf_jit_stack_offsetof(ctx, bpf_to_ppc(i))));

- if (ctx->arena_vm_start)
- EMIT(PPC_RAW_STD(bpf_to_ppc(ARENA_VM_START), _R1,
+ if (ctx->exception_boundary || ctx->arena_vm_start)
+ EMIT(PPC_RAW_STD(bpf_to_ppc(ARENA_VM_START), _R1,
bpf_jit_stack_offsetof(ctx, bpf_to_ppc(ARENA_VM_START))));

- /* Setup frame pointer to point to the bpf stack area */
- if (bpf_is_seen_register(ctx, bpf_to_ppc(BPF_REG_FP)))
- EMIT(PPC_RAW_ADDI(bpf_to_ppc(BPF_REG_FP), _R1,
+ /* Setup frame pointer to point to the bpf stack area */
+ if (bpf_is_seen_register(ctx, bpf_to_ppc(BPF_REG_FP)))
+ EMIT(PPC_RAW_ADDI(bpf_to_ppc(BPF_REG_FP), _R1,
STACK_FRAME_MIN_SIZE + ctx->stack_size));
+ } else {
+ /*
+ * Exception callback receives Frame Pointer of main
+ * program as third arg
+ */
+ EMIT(PPC_RAW_MR(_R1, _R5));
+ }

if (ctx->arena_vm_start)
PPC_LI64(bpf_to_ppc(ARENA_VM_START), ctx->arena_vm_start);
@@ -218,17 +229,25 @@ static void bpf_jit_emit_common_epilogue(u32 *image, struct codegen_context *ctx

/* Restore NVRs */
for (i = BPF_REG_6; i <= BPF_REG_10; i++)
- if (bpf_is_seen_register(ctx, bpf_to_ppc(i)))
+ if (ctx->exception_cb || bpf_is_seen_register(ctx, bpf_to_ppc(i)))
EMIT(PPC_RAW_LD(bpf_to_ppc(i), _R1, bpf_jit_stack_offsetof(ctx, bpf_to_ppc(i))));

- if (ctx->arena_vm_start)
+ if (ctx->exception_cb || ctx->arena_vm_start)
EMIT(PPC_RAW_LD(bpf_to_ppc(ARENA_VM_START), _R1,
bpf_jit_stack_offsetof(ctx, bpf_to_ppc(ARENA_VM_START))));

+ if (ctx->exception_cb) {
+ /*
+ * LR value from boundary-frame is received as second parameter
+ * in exception callback.
+ */
+ EMIT(PPC_RAW_MTLR(_R4));
+ }
+
/* Tear down our stack frame */
if (bpf_has_stack_frame(ctx)) {
EMIT(PPC_RAW_ADDI(_R1, _R1, BPF_PPC_STACKFRAME + ctx->stack_size));
- if (ctx->seen & SEEN_FUNC) {
+ if (ctx->seen & SEEN_FUNC || ctx->exception_cb) {
EMIT(PPC_RAW_LD(_R0, _R1, PPC_LR_STKOFF));
EMIT(PPC_RAW_MTLR(_R0));
}
--
2.48.1