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Date: Fri, 14 Aug 2020 17:53:28 -0700 From: Sami Tolvanen <samitolvanen@...gle.com> To: Nick Desaulniers <ndesaulniers@...gle.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, Dávid Bolvanský <david.bolvansky@...il.com>, Eli Friedman <efriedma@...cinc.com>, stable@...r.kernel.org, Joe Perches <joe@...ches.com>, Tony Luck <tony.luck@...el.com>, Yury Norov <yury.norov@...il.com>, Daniel Axtens <dja@...ens.net>, Arvind Sankar <nivedita@...m.mit.edu>, Dan Williams <dan.j.williams@...el.com>, "Joel Fernandes (Google)" <joel@...lfernandes.org>, Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Kees Cook <keescook@...omium.org>, Alexandru Ardelean <alexandru.ardelean@...log.com>, LKML <linux-kernel@...r.kernel.org>, clang-built-linux <clang-built-linux@...glegroups.com> Subject: Re: [PATCH] lib/string.c: implement stpcpy Hi Nick, On Fri, Aug 14, 2020 at 5:24 PM Nick Desaulniers <ndesaulniers@...gle.com> wrote: > > LLVM implemented a recent "libcall optimization" that lowers calls to > `sprintf(dest, "%s", str)` where the return value is used to > `stpcpy(dest, str) - dest`. This generally avoids the machinery involved > in parsing format strings. > > `stpcpy` is just like `strcpy` except: > 1. it returns the pointer to the new tail of `dest`. This allows you to > chain multiple calls to `stpcpy` in one statement. > 2. it requires the parameters not to overlap. Calling `sprintf` with > overlapping arguments was clarified in ISO C99 and POSIX.1-2001 to be > undefined behavior. > > `stpcpy` was first standardized in POSIX.1-2008. > > Implement this so that we don't observe linkage failures due to missing > symbol definitions for `stpcpy`. > > Similar to last year's fire drill with: > commit 5f074f3e192f ("lib/string.c: implement a basic bcmp") > > This optimization was introduced into clang-12. > > Cc: stable@...r.kernel.org > Link: https://bugs.llvm.org/show_bug.cgi?id=47162 > Link: https://github.com/ClangBuiltLinux/linux/issues/1126 > Link: https://man7.org/linux/man-pages/man3/stpcpy.3.html > Link: https://pubs.opengroup.org/onlinepubs/9699919799/functions/stpcpy.html > Link: https://reviews.llvm.org/D85963 > Reported-by: Sami Tolvanen <samitolvanen@...gle.com> > Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com> > --- > include/linux/string.h | 3 +++ > lib/string.c | 23 +++++++++++++++++++++++ > 2 files changed, 26 insertions(+) Thank you for the patch! I can confirm that this fixes the build for me with ToT Clang. Tested-by: Sami Tolvanen <samitolvanen@...gle.com> Sami
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