[PATCH v2 1/2] powerpc64/bpf: Implement JIT support for private stack
kernel test robot
lkp at intel.com
Thu Feb 26 04:13:18 AEDT 2026
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 v7.0-rc1 next-20260224]
[cannot apply to bpf-next/net powerpc/fixes]
[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-powerpc64/20260225-184532
base: https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
patch link: https://lore.kernel.org/r/20260225153950.15331-1-adubey%40linux.ibm.com
patch subject: [PATCH v2 1/2] powerpc64/bpf: Implement JIT support for private stack
config: powerpc-randconfig-r123-20260225 (https://download.01.org/0day-ci/archive/20260226/202602260116.5ljOxwdH-lkp@intel.com/config)
compiler: clang version 23.0.0git (https://github.com/llvm/llvm-project 9a109fbb6e184ec9bcce10615949f598f4c974a9)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260226/202602260116.5ljOxwdH-lkp@intel.com/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 <lkp at intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202602260116.5ljOxwdH-lkp@intel.com/
All warnings (new ones prefixed by >>):
>> arch/powerpc/net/bpf_jit_comp.c:222:7: warning: variable 'addrs' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
222 | if (!priv_stack_ptr) {
| ^~~~~~~~~~~~~~~
arch/powerpc/net/bpf_jit_comp.c:370:9: note: uninitialized use occurs here
370 | kfree(addrs);
| ^~~~~
arch/powerpc/net/bpf_jit_comp.c:222:3: note: remove the 'if' if its condition is always false
222 | if (!priv_stack_ptr) {
| ^~~~~~~~~~~~~~~~~~~~~~
223 | fp = org_fp;
| ~~~~~~~~~~~~
224 | goto out_priv_stack;
| ~~~~~~~~~~~~~~~~~~~~
225 | }
| ~
arch/powerpc/net/bpf_jit_comp.c:171:12: note: initialize the variable 'addrs' to silence this warning
171 | u32 *addrs;
| ^
| = NULL
1 warning generated.
vim +222 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_obj(*jit_data);
204 if (!jit_data) {
205 fp = org_fp;
206 goto out;
207 }
208 fp->aux->jit_data = jit_data;
209 }
210
211 priv_stack_ptr = fp->aux->priv_stack_ptr;
212 if (!priv_stack_ptr && fp->aux->jits_use_priv_stack) {
213 /*
214 * Allocate private stack of size equivalent to
215 * verifier-calculated stack size plus two memory
216 * guard regions to detect private stack overflow
217 * and underflow.
218 */
219 priv_stack_alloc_size = round_up(fp->aux->stack_depth, 16) +
220 2 * PRIV_STACK_GUARD_SZ;
221 priv_stack_ptr = __alloc_percpu_gfp(priv_stack_alloc_size, 16, GFP_KERNEL);
> 222 if (!priv_stack_ptr) {
223 fp = org_fp;
224 goto out_priv_stack;
225 }
226
227 priv_stack_init_guard(priv_stack_ptr, priv_stack_alloc_size);
228 fp->aux->priv_stack_ptr = priv_stack_ptr;
229 }
230
231 flen = fp->len;
232 addrs = jit_data->addrs;
233 if (addrs) {
234 cgctx = jit_data->ctx;
235 /*
236 * JIT compiled to a writable location (image/code_base) first.
237 * It is then moved to the readonly final location (fimage/fcode_base)
238 * using instruction patching.
239 */
240 fimage = jit_data->fimage;
241 fhdr = jit_data->fhdr;
242 proglen = jit_data->proglen;
243 hdr = jit_data->hdr;
244 image = (void *)hdr + ((void *)fimage - (void *)fhdr);
245 extra_pass = true;
246 /* During extra pass, ensure index is reset before repopulating extable entries */
247 cgctx.exentry_idx = 0;
248 goto skip_init_ctx;
249 }
250
251 addrs = kcalloc(flen + 1, sizeof(*addrs), GFP_KERNEL);
252 if (addrs == NULL) {
253 fp = org_fp;
254 goto out_addrs;
255 }
256
257 memset(&cgctx, 0, sizeof(struct codegen_context));
258 bpf_jit_init_reg_mapping(&cgctx);
259
260 /* Make sure that the stack is quadword aligned. */
261 cgctx.stack_size = round_up(fp->aux->stack_depth, 16);
262 cgctx.arena_vm_start = bpf_arena_get_kern_vm_start(fp->aux->arena);
263 cgctx.user_vm_start = bpf_arena_get_user_vm_start(fp->aux->arena);
264 cgctx.is_subprog = bpf_is_subprog(fp);
265 cgctx.exception_boundary = fp->aux->exception_boundary;
266 cgctx.exception_cb = fp->aux->exception_cb;
267 cgctx.priv_sp = priv_stack_ptr;
268
269 /* Scouting faux-generate pass 0 */
270 if (bpf_jit_build_body(fp, NULL, NULL, &cgctx, addrs, 0, false)) {
271 /* We hit something illegal or unsupported. */
272 fp = org_fp;
273 goto out_addrs;
274 }
275
276 /*
277 * If we have seen a tail call, we need a second pass.
278 * This is because bpf_jit_emit_common_epilogue() is called
279 * from bpf_jit_emit_tail_call() with a not yet stable ctx->seen.
280 * We also need a second pass if we ended up with too large
281 * a program so as to ensure BPF_EXIT branches are in range.
282 */
283 if (cgctx.seen & SEEN_TAILCALL || !is_offset_in_branch_range((long)cgctx.idx * 4)) {
284 cgctx.idx = 0;
285 if (bpf_jit_build_body(fp, NULL, NULL, &cgctx, addrs, 0, false)) {
286 fp = org_fp;
287 goto out_addrs;
288 }
289 }
290
291 bpf_jit_realloc_regs(&cgctx);
292 /*
293 * Pretend to build prologue, given the features we've seen. This will
294 * update ctgtx.idx as it pretends to output instructions, then we can
295 * calculate total size from idx.
296 */
297 bpf_jit_build_prologue(NULL, &cgctx);
298 addrs[fp->len] = cgctx.idx * 4;
299 bpf_jit_build_epilogue(NULL, &cgctx);
300
301 fixup_len = fp->aux->num_exentries * BPF_FIXUP_LEN * 4;
302 extable_len = fp->aux->num_exentries * sizeof(struct exception_table_entry);
303
304 proglen = cgctx.idx * 4;
305 alloclen = proglen + FUNCTION_DESCR_SIZE + fixup_len + extable_len;
306
307 fhdr = bpf_jit_binary_pack_alloc(alloclen, &fimage, 4, &hdr, &image,
308 bpf_jit_fill_ill_insns);
309 if (!fhdr) {
310 fp = org_fp;
311 goto out_addrs;
312 }
313
314 if (extable_len)
315 fp->aux->extable = (void *)fimage + FUNCTION_DESCR_SIZE + proglen + fixup_len;
316
317 skip_init_ctx:
318 code_base = (u32 *)(image + FUNCTION_DESCR_SIZE);
319 fcode_base = (u32 *)(fimage + FUNCTION_DESCR_SIZE);
320
321 /* Code generation passes 1-2 */
322 for (pass = 1; pass < 3; pass++) {
323 /* Now build the prologue, body code & epilogue for real. */
324 cgctx.idx = 0;
325 cgctx.alt_exit_addr = 0;
326 bpf_jit_build_prologue(code_base, &cgctx);
327 if (bpf_jit_build_body(fp, code_base, fcode_base, &cgctx, addrs, pass,
328 extra_pass)) {
329 bpf_arch_text_copy(&fhdr->size, &hdr->size, sizeof(hdr->size));
330 bpf_jit_binary_pack_free(fhdr, hdr);
331 fp = org_fp;
332 goto out_addrs;
333 }
334 bpf_jit_build_epilogue(code_base, &cgctx);
335
336 if (bpf_jit_enable > 1)
337 pr_info("Pass %d: shrink = %d, seen = 0x%x\n", pass,
338 proglen - (cgctx.idx * 4), cgctx.seen);
339 }
340
341 if (bpf_jit_enable > 1)
342 /*
343 * Note that we output the base address of the code_base
344 * rather than image, since opcodes are in code_base.
345 */
346 bpf_jit_dump(flen, proglen, pass, code_base);
347
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