Hi Nick,
On Fri, Aug 14, 2020 at 5:24 PM Nick Desaulniers ndesaulniers@google.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:
- it returns the pointer to the new tail of `dest`. This allows you to chain multiple calls to `stpcpy` in one statement.
- 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@vger.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@google.com Signed-off-by: Nick Desaulniers ndesaulniers@google.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@google.com
Sami