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Date: Tue, 2 Aug 2022 09:13:32 -0700
From: Nick Desaulniers <ndesaulniers@...gle.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>, llvm@...ts.linux.dev,
kbuild-all@...ts.01.org, linux-kernel@...r.kernel.org,
kernel test robot <lkp@...el.com>
Subject: Re: [tglx-devel:depthtracking 35/38] arch/x86/kernel/callthunks.c:411:7:
warning: variable 'ret' is used uninitialized whenever 'if' condition is true
On Thu, Jul 14, 2022 at 5:24 AM kernel test robot <lkp@...el.com> wrote:
>
> tree: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git depthtracking
> head: 81d2c1b17a61bfeca4b92a5d6e1fb6f5ff464826
> commit: 57b6f2ca7edda679f0a9fe58087ecc9dd9f8dafb [35/38] kprobes: Add callthunk blacklisting
> config: x86_64-randconfig-a005 (https://download.01.org/0day-ci/archive/20220714/202207142029.dpdKYPLD-lkp@intel.com/config)
> compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project 5e61b9c556267086ef9b743a0b57df302eef831b)
> reproduce (this is a W=1 build):
> wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> chmod +x ~/bin/make.cross
> # https://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git/commit/?id=57b6f2ca7edda679f0a9fe58087ecc9dd9f8dafb
> git remote add tglx-devel https://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git
> git fetch --no-tags tglx-devel depthtracking
> git checkout 57b6f2ca7edda679f0a9fe58087ecc9dd9f8dafb
> # save the config file
> mkdir build_dir && cp config build_dir/.config
> COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash arch/x86/kernel/
>
> If you fix the issue, kindly add following tag where applicable
> Reported-by: kernel test robot <lkp@...el.com>
>
> All warnings (new ones prefixed by >>):
>
> >> arch/x86/kernel/callthunks.c:411:7: warning: variable 'ret' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
> if (!vbuf)
> ^~~~~
> arch/x86/kernel/callthunks.c:475:9: note: uninitialized use occurs here
> return ret;
> ^~~
> arch/x86/kernel/callthunks.c:411:3: note: remove the 'if' if its condition is always false
> if (!vbuf)
> ^~~~~~~~~~
> arch/x86/kernel/callthunks.c:375:9: note: initialize the variable 'ret' to silence this warning
> int ret, text_size, size;
> ^
> = 0
> 1 warning generated.
>
>
> vim +411 arch/x86/kernel/callthunks.c
Looks legit.
>
> 25cd68b763b44e Thomas Gleixner 2022-06-18 367
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 368 static __init_or_module int callthunks_setup(struct callthunk_sites *cs,
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 369 struct module_layout *layout)
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 370 {
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 371 u8 *tp, *thunk, *buffer, *vbuf = NULL;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 372 struct paravirt_patch_site *pv;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 373 unsigned int nthunks, bitpos;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 374 struct thunk_mem_area *area;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 375 int ret, text_size, size;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 376 s32 *s;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 377
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 378 lockdep_assert_held(&text_mutex);
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 379
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 380 prdbg("Setup %s\n", layout_getname(layout));
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 381 /* Calculate the number of thunks required */
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 382 nthunks = cs->syms_end - cs->syms_start;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 383 nthunks += cs->pv_end - cs->pv_start;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 384
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 385 /*
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 386 * thunk_size can be 0 when there are no intra module calls,
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 387 * but there might be still sites to patch.
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 388 */
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 389 if (!nthunks)
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 390 goto patch;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 391
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 392 area = callthunks_alloc(nthunks);
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 393 if (!area)
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 394 return -ENOMEM;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 395
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 396 bitpos = area->start;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 397 thunk = area->tmem->base + bitpos * callthunk_desc.thunk_size;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 398 tp = thunk;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 399
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 400 prdbg("Thunk %px\n", tp);
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 401 /*
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 402 * If the memory area is already RX, use a temporary
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 403 * buffer. Otherwise just copy into the unused area
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 404 */
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 405 if (!area->tmem->is_rx) {
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 406 prdbg("Using thunk direct\n");
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 407 buffer = thunk;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 408 } else {
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 409 size = nthunks * callthunk_desc.thunk_size;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 410 vbuf = vmalloc(size);
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 @411 if (!vbuf)
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 412 goto fail;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 413 memset(vbuf, INT3_INSN_OPCODE, size);
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 414 buffer = vbuf;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 415 prdbg("Using thunk vbuf %px\n", vbuf);
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 416 }
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 417
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 418 for (s = cs->syms_start; s < cs->syms_end; s++, bitpos++) {
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 419 void *dest = (void *)s + *s;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 420
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 421 ret = callthunk_setup_one(dest, tp, buffer, layout);
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 422 if (ret)
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 423 goto fail;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 424 buffer += callthunk_desc.thunk_size;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 425 tp += callthunk_desc.thunk_size;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 426 bitmap_set(area->tmem->map, bitpos, 1);
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 427 area->nthunks++;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 428 }
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 429
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 430 for (pv = cs->pv_start; pv < cs->pv_end; pv++, bitpos++) {
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 431 ret = callthunk_setup_one(pv->instr, tp, buffer, layout);
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 432 if (ret)
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 433 goto fail;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 434 buffer += callthunk_desc.thunk_size;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 435 tp += callthunk_desc.thunk_size;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 436 bitmap_set(area->tmem->map, bitpos, 1);
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 437 area->nthunks++;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 438 }
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 439
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 440 text_size = tp - thunk;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 441 prdbg("Thunk %px .. %px 0x%x\n", thunk, tp, text_size);
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 442
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 443 /*
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 444 * If thunk memory is already RX, poke the buffer into it.
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 445 * Otherwise make the memory RX.
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 446 */
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 447 if (vbuf)
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 448 text_poke_copy_locked(thunk, vbuf, text_size);
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 449 else
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 450 callthunk_area_set_rx(area);
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 451 sync_core();
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 452
> 25cd68b763b44e Thomas Gleixner 2022-06-18 453 ret = callthunk_set_modname(layout);
> 25cd68b763b44e Thomas Gleixner 2022-06-18 454 if (ret)
> 25cd68b763b44e Thomas Gleixner 2022-06-18 455 goto fail;
> 25cd68b763b44e Thomas Gleixner 2022-06-18 456
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 457 layout->base = thunk;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 458 layout->size = text_size;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 459 layout->text_size = text_size;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 460 layout->arch_data = area;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 461
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 462 vfree(vbuf);
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 463
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 464 patch:
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 465 prdbg("Patching call sites %s\n", layout_getname(layout));
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 466 patch_call_sites(cs->call_start, cs->call_end, layout);
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 467 patch_paravirt_call_sites(cs->pv_start, cs->pv_end, layout);
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 468 prdbg("Patching call sites done%s\n", layout_getname(layout));
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 469 return 0;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 470
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 471 fail:
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 472 WARN_ON_ONCE(ret);
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 473 callthunk_free(area, false);
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 474 vfree(vbuf);
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 475 return ret;
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 476 }
> 02b09aaafc9a43 Thomas Gleixner 2022-06-18 477
>
> :::::: The code at line 411 was first introduced by commit
> :::::: 02b09aaafc9a439ca50cc049e98f7cc945e5b294 x86/callthunks: Add call patching for call depth tracking
>
> :::::: TO: Thomas Gleixner <tglx@...utronix.de>
> :::::: CC: Thomas Gleixner <tglx@...utronix.de>
>
> --
> 0-DAY CI Kernel Test Service
> https://01.org/lkp
>
--
Thanks,
~Nick Desaulniers
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