nickdesaulniers added a comment. Testing Diff 342071 on the mainline Linux kernel, just building x86_64 defconfig triggers 19 instances of this warning; all look legit. ;)
In D100581#2730708 <https://reviews.llvm.org/D100581#2730708>, @dblaikie wrote: > In D100581#2730557 <https://reviews.llvm.org/D100581#2730557>, > @nickdesaulniers wrote: > >> I see lots of instances from the kernel that look like this when reduced: >> >> $ cat foo.c >> int page; >> int put_page_testzero(int); >> void foo (void) { >> int zeroed; >> zeroed = put_page_testzero(page); >> ((void)(sizeof(( long)(!zeroed)))); >> } >> $ clang -c -Wall foo.c >> foo.c:4:7: warning: variable 'zeroed' set but not used >> [-Wunused-but-set-variable] >> int zeroed; >> ^ > > Any idea what the purpose of this code is/why it's not a reasonable thing to > warn on? include/linux/build_bug.h: 25 /* 26 * BUILD_BUG_ON_INVALID() permits the compiler to check the validity of the 27 * expression but avoids the generation of any code, even if that expression 28 * has side-effects. 29 */ 30 #define BUILD_BUG_ON_INVALID(e) ((void)(sizeof((__force long)(e)))) include/linux/mmdebug.h: 57 #define VM_BUG_ON(cond) BUILD_BUG_ON_INVALID(cond) mm/internal.h: 410 static inline unsigned long 411 vma_address(struct page *page, struct vm_area_struct *vma) 412 { 413 unsigned long start, end; 414 415 start = __vma_address(page, vma); 416 end = start + thp_size(page) - PAGE_SIZE; 417 418 /* page should be within @vma mapping range */ 419 VM_BUG_ON_VMA(end < vma->vm_start || start >= vma->vm_end, vma); The warning (in previous revisions was triggering on `end` in `vma_address`. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D100581/new/ https://reviews.llvm.org/D100581 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
