Subject: Re: [PATCH 1/2] powerpc64/bpf: Implement JIT support for private stack

From: adubey <[email-masked]>
Date: Wed, 25 Feb 2026 16:14:29 +0530

On 2026-02-17 00:44, kernel test robot wrote:
> Hi,
> 
> kernel test robot noticed the following build warnings:
> 
> [auto build test WARNING on bpf-next/master]
> [also build test WARNING on bpf/master powerpc/next linus/master 
> next-20260216]
> [cannot apply to bpf-next/net powerpc/fixes v6.19]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch#_base_tree_information]
> 
> url:
> https://github.com/intel-lab-lkp/linux/commits/adubey-linux-ibm-com/selftests-bpf-Enable-private-stack-tests-for-powerpc64/20260216-182353
> base:   
> https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
> patch link:
> https://lore.kernel.org/r/20260216152234.36632-1-adubey%40linux.ibm.com
> patch subject: [PATCH 1/2] powerpc64/bpf: Implement JIT support for
> private stack
> config: powerpc-randconfig-001-20260217
> (https://download.01.org/0day-ci/archive/20260217/[email-masked]/config)
> compiler: powerpc-linux-gcc (GCC) 8.5.0
> reproduce (this is a W=1 build):
> (https://download.01.org/0day-ci/archive/20260217/[email-masked]/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new 
> version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <[email-masked]>
> | Closes:
> https://lore.kernel.org/oe-kbuild-all/[email-masked]/
> 
> All warnings (new ones prefixed by >>):
> 
>    arch/powerpc/net/bpf_jit_comp.c: In function 'bpf_int_jit_compile':
>>> arch/powerpc/net/bpf_jit_comp.c:266:35: warning: cast from pointer to 
>>> integer of different size [-Wpointer-to-int-cast]
>      cgctx.priv_sp = priv_stack_ptr ? (u64)priv_stack_ptr : 0;
>                                       ^
> 
> 
> vim +266 arch/powerpc/net/bpf_jit_comp.c
> 
>    164
>    165	struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
>    166	{
>    167		u32 proglen;
>    168		u32 alloclen;
>    169		u8 *image = NULL;
>    170		u32 *code_base;
>    171		u32 *addrs;
>    172		struct powerpc_jit_data *jit_data;
>    173		struct codegen_context cgctx;
>    174		int pass;
>    175		int flen;
>    176		int priv_stack_alloc_size;
>    177		void __percpu *priv_stack_ptr = NULL;
>    178		struct bpf_binary_header *fhdr = NULL;
>    179		struct bpf_binary_header *hdr = NULL;
>    180		struct bpf_prog *org_fp = fp;
>    181		struct bpf_prog *tmp_fp;
>    182		bool bpf_blinded = false;
>    183		bool extra_pass = false;
>    184		u8 *fimage = NULL;
>    185		u32 *fcode_base;
>    186		u32 extable_len;
>    187		u32 fixup_len;
>    188
>    189		if (!fp->jit_requested)
>    190			return org_fp;
>    191
>    192		tmp_fp = bpf_jit_blind_constants(org_fp);
>    193		if (IS_ERR(tmp_fp))
>    194			return org_fp;
>    195
>    196		if (tmp_fp != org_fp) {
>    197			bpf_blinded = true;
>    198			fp = tmp_fp;
>    199		}
>    200
>    201		jit_data = fp->aux->jit_data;
>    202		if (!jit_data) {
>    203			jit_data = kzalloc(sizeof(*jit_data), GFP_KERNEL);
>    204			if (!jit_data) {
>    205				fp = org_fp;
>    206				goto out;
>    207			}
>    208			fp->aux->jit_data = jit_data;
>    209		}
>    210
>    211		if (!priv_stack_ptr && fp->aux->jits_use_priv_stack) {
>    212			/*
>    213			 * Allocate private stack of size equivalent to
>    214			 * verifier-calculated stack size plus two memory
>    215			 * guard regions to detect private stack overflow
>    216			 * and underflow.
>    217			 */
>    218			priv_stack_alloc_size = round_up(fp->aux->stack_depth, 16) +
>    219								2 * PRIV_STACK_GUARD_SZ;
>    220			priv_stack_ptr = __alloc_percpu_gfp(priv_stack_alloc_size,
> 16, GFP_KERNEL);
>    221			if (!priv_stack_ptr) {
>    222				fp = org_fp;
>    223				goto out_priv_stack;
>    224			}
>    225
>    226			priv_stack_init_guard(priv_stack_ptr, priv_stack_alloc_size);
>    227			fp->aux->priv_stack_ptr = priv_stack_ptr;
>    228		}
>    229
>    230		flen = fp->len;
>    231		addrs = jit_data->addrs;
>    232		if (addrs) {
>    233			cgctx = jit_data->ctx;
>    234			/*
>    235			 * JIT compiled to a writable location (image/code_base) 
> first.
>    236			 * It is then moved to the readonly final location 
> (fimage/fcode_base)
>    237			 * using instruction patching.
>    238			 */
>    239			fimage = jit_data->fimage;
>    240			fhdr = jit_data->fhdr;
>    241			proglen = jit_data->proglen;
>    242			hdr = jit_data->hdr;
>    243			image = (void *)hdr + ((void *)fimage - (void *)fhdr);
>    244			extra_pass = true;
>    245			/* During extra pass, ensure index is reset before
> repopulating extable entries */
>    246			cgctx.exentry_idx = 0;
>    247			goto skip_init_ctx;
>    248		}
>    249
>    250		addrs = kcalloc(flen + 1, sizeof(*addrs), GFP_KERNEL);
>    251		if (addrs == NULL) {
>    252			fp = org_fp;
>    253			goto out_addrs;
>    254		}
>    255
>    256		memset(&cgctx, 0, sizeof(struct codegen_context));
>    257		bpf_jit_init_reg_mapping(&cgctx);
>    258
>    259		/* Make sure that the stack is quadword aligned. */
>    260		cgctx.stack_size = round_up(fp->aux->stack_depth, 16);
>    261		cgctx.arena_vm_start = 
> bpf_arena_get_kern_vm_start(fp->aux->arena);
>    262		cgctx.user_vm_start = 
> bpf_arena_get_user_vm_start(fp->aux->arena);
>    263		cgctx.is_subprog = bpf_is_subprog(fp);
>    264		cgctx.exception_boundary = fp->aux->exception_boundary;
>    265		cgctx.exception_cb = fp->aux->exception_cb;
>  > 266		cgctx.priv_sp = priv_stack_ptr ? (u64)priv_stack_ptr : 0;
>    267
>    268		/* Scouting faux-generate pass 0 */
>    269		if (bpf_jit_build_body(fp, NULL, NULL, &cgctx, addrs, 0, 
> false)) {
>    270			/* We hit something illegal or unsupported. */
>    271			fp = org_fp;
>    272			goto out_addrs;
>    273		}
>    274
>    275		/*
>    276		 * If we have seen a tail call, we need a second pass.
>    277		 * This is because bpf_jit_emit_common_epilogue() is called
>    278		 * from bpf_jit_emit_tail_call() with a not yet stable 
> ctx->seen.
>    279		 * We also need a second pass if we ended up with too large
>    280		 * a program so as to ensure BPF_EXIT branches are in range.
>    281		 */
>    282		if (cgctx.seen & SEEN_TAILCALL ||
> !is_offset_in_branch_range((long)cgctx.idx * 4)) {
>    283			cgctx.idx = 0;
>    284			if (bpf_jit_build_body(fp, NULL, NULL, &cgctx, addrs, 0, 
> false)) {
>    285				fp = org_fp;
>    286				goto out_addrs;
>    287			}
>    288		}
>    289
>    290		bpf_jit_realloc_regs(&cgctx);
>    291		/*
>    292		 * Pretend to build prologue, given the features we've seen.  
> This will
>    293		 * update ctgtx.idx as it pretends to output instructions, then 
> we can
>    294		 * calculate total size from idx.
>    295		 */
>    296		bpf_jit_build_prologue(NULL, &cgctx);
>    297		addrs[fp->len] = cgctx.idx * 4;
>    298		bpf_jit_build_epilogue(NULL, &cgctx);
>    299
>    300		fixup_len = fp->aux->num_exentries * BPF_FIXUP_LEN * 4;
>    301		extable_len = fp->aux->num_exentries * sizeof(struct
> exception_table_entry);
>    302
>    303		proglen = cgctx.idx * 4;
>    304		alloclen = proglen + FUNCTION_DESCR_SIZE + fixup_len + 
> extable_len;
>    305
>    306		fhdr = bpf_jit_binary_pack_alloc(alloclen, &fimage, 4, &hdr, 
> &image,
>    307						      bpf_jit_fill_ill_insns);
>    308		if (!fhdr) {
>    309			fp = org_fp;
>    310			goto out_addrs;
>    311		}
>    312
>    313		if (extable_len)
>    314			fp->aux->extable = (void *)fimage + FUNCTION_DESCR_SIZE +
> proglen + fixup_len;
>    315
>    316	skip_init_ctx:
>    317		code_base = (u32 *)(image + FUNCTION_DESCR_SIZE);
>    318		fcode_base = (u32 *)(fimage + FUNCTION_DESCR_SIZE);
>    319
>    320		/* Code generation passes 1-2 */
>    321		for (pass = 1; pass < 3; pass++) {
>    322			/* Now build the prologue, body code & epilogue for real. */
>    323			cgctx.idx = 0;
>    324			cgctx.alt_exit_addr = 0;
>    325			bpf_jit_build_prologue(code_base, &cgctx);
>    326			if (bpf_jit_build_body(fp, code_base, fcode_base, &cgctx, 
> addrs, pass,
>    327					       extra_pass)) {
>    328				bpf_arch_text_copy(&fhdr->size, &hdr->size, 
> sizeof(hdr->size));
>    329				bpf_jit_binary_pack_free(fhdr, hdr);
>    330				fp = org_fp;
>    331				goto out_addrs;
>    332			}
>    333			bpf_jit_build_epilogue(code_base, &cgctx);
>    334
>    335			if (bpf_jit_enable > 1)
>    336				pr_info("Pass %d: shrink = %d, seen = 0x%x\n", pass,
>    337					proglen - (cgctx.idx * 4), cgctx.seen);
>    338		}
>    339
>    340		if (bpf_jit_enable > 1)
>    341			/*
>    342			 * Note that we output the base address of the code_base
>    343			 * rather than image, since opcodes are in code_base.
>    344			 */
>    345			bpf_jit_dump(flen, proglen, pass, code_base);
>    346
Fixed in v2 : 
https://lore.kernel.org/bpf/[email-masked]/

-Abhishek