Thank you Yuri for insightful comments! Please see my responses inline... On 12/5/24 21:53, Yury Norov wrote: > On Thu, Dec 05, 2024 at 06:04:09PM +0530, Nilay Shroff wrote: >> While building the powerpc code using gcc 13, I came across following >> errors generated for kernel/padata.c file: >> >> CC kernel/padata.o >> In file included from ./include/linux/string.h:390, >> from ./arch/powerpc/include/asm/paca.h:16, >> from ./arch/powerpc/include/asm/current.h:13, >> from ./include/linux/thread_info.h:23, >> from ./include/asm-generic/preempt.h:5, >> from ./arch/powerpc/include/generated/asm/preempt.h:1, >> from ./include/linux/preempt.h:79, >> from ./include/linux/spinlock.h:56, >> from ./include/linux/swait.h:7, >> from ./include/linux/completion.h:12, >> from kernel/padata.c:14: >> In function ‘bitmap_copy’, >> inlined from ‘cpumask_copy’ at ./include/linux/cpumask.h:839:2, >> inlined from ‘__padata_set_cpumasks’ at kernel/padata.c:730:2: >> ./include/linux/fortify-string.h:114:33: error: ‘__builtin_memcpy’ reading between 257 and 536870904 bytes from a region of size 256 [-Werror=stringop-overread] >> 114 | #define __underlying_memcpy __builtin_memcpy >> | ^ >> ./include/linux/fortify-string.h:633:9: note: in expansion of macro ‘__underlying_memcpy’ >> 633 | __underlying_##op(p, q, __fortify_size); \ >> | ^~~~~~~~~~~~~ >> ./include/linux/fortify-string.h:678:26: note: in expansion of macro ‘__fortify_memcpy_chk’ >> 678 | #define memcpy(p, q, s) __fortify_memcpy_chk(p, q, s, \ >> | ^~~~~~~~~~~~~~~~~~~~ >> ./include/linux/bitmap.h:259:17: note: in expansion of macro ‘memcpy’ >> 259 | memcpy(dst, src, len); >> | ^~~~~~ >> kernel/padata.c: In function ‘__padata_set_cpumasks’: >> kernel/padata.c:713:48: note: source object ‘pcpumask’ of size [0, 256] >> 713 | cpumask_var_t pcpumask, >> | ~~~~~~~~~~~~~~^~~~~~~~ >> In function ‘bitmap_copy’, >> inlined from ‘cpumask_copy’ at ./include/linux/cpumask.h:839:2, >> inlined from ‘__padata_set_cpumasks’ at kernel/padata.c:730:2: >> ./include/linux/fortify-string.h:114:33: error: ‘__builtin_memcpy’ reading between 257 and 536870904 bytes from a region of size 256 [-Werror=stringop-overread] >> 114 | #define __underlying_memcpy __builtin_memcpy >> | ^ >> ./include/linux/fortify-string.h:633:9: note: in expansion of macro ‘__underlying_memcpy’ >> 633 | __underlying_##op(p, q, __fortify_size); \ >> | ^~~~~~~~~~~~~ >> ./include/linux/fortify-string.h:678:26: note: in expansion of macro ‘__fortify_memcpy_chk’ >> 678 | #define memcpy(p, q, s) __fortify_memcpy_chk(p, q, s, \ >> | ^~~~~~~~~~~~~~~~~~~~ >> ./include/linux/bitmap.h:259:17: note: in expansion of macro ‘memcpy’ >> 259 | memcpy(dst, src, len); >> | ^~~~~~ >> kernel/padata.c: In function ‘__padata_set_cpumasks’: >> kernel/padata.c:713:48: note: source object ‘pcpumask’ of size [0, 256] >> 713 | cpumask_var_t pcpumask, >> | ~~~~~~~~~~~~~~^~~~~~~~ >> >> Apparently, above errors only manifests with GCC 13.x and config option >> CONFIG_FORTIFY_SOURCE. Furthermore, if I use gcc 11.x or gcc 12.x then I >> don't encounter above errors. Prima facie, these errors appear to be false- > > If it works for pre-GCC13, and likely for clang, you shouldn't disable it > for them. It should be enabled for CONFIG_FORTIFY_SOURCE=n, as well. > > Check config CC_NO_ARRAY_BOUNDS for an example of how versioned flags > are implemented. > >> positive. Brian informed me that currently some efforts are underway by >> GCC developers to emit more verbose information when GCC detects string >> overflow errors and that might help to further narrow down the root cause >> of this error. > > I'm 100% sure that Brian is a great person and his information is > absolutely correct and complete. But this is just not how we write > commit messages. > > Please avoid personal references, vague statements and news from > the future. > Sure, I would do the needful for future patches. >> So for now, silence these errors using -Wno-stringop- >> overread gcc option while building kernel/padata.c file until we find the >> root cause. > > You didn't provide any evidence that this warning is specific for padata. > Let me just show you the test matrix for the stringop-overread error: ARCH PowerPC: compiler CONFIG_FORTIFY_SOURCE -Werror=stringop-overread gcc 11.x Y N gcc 11.x N N gcc 12.x Y N gcc 12.x N N gcc 13.x Y Y gcc 13.x N N clang 18.x Y N clang 18.x N N ARCH x86_64: compiler CONFIG_FORTIFY_SOURCE -Werror=stringop-overread gcc 11.x Y N gcc 11.x N N gcc 12.x Y N gcc 12.x N N gcc 13.x Y N gcc 13.x N N clang 18.x Y N clang 18.x N N
