On Fri, Jul 19, 2019 at 11:44 AM Arnd Bergmann <a...@arndb.de> wrote: > > On Fri, Jul 19, 2019 at 8:31 PM Josh Poimboeuf <jpoim...@redhat.com> wrote: > > > > On Fri, Jul 19, 2019 at 11:23:16AM -0700, Nick Desaulniers wrote: > > > On Fri, Jul 19, 2019 at 11:10 AM Arnd Bergmann <a...@arndb.de> wrote: > > > > > > > > A lot of objtool fixes showed up in linux-next, so I looked at some > > > > remaining ones. > > > > This one comes a lot up in some configurations > > > > > > > > https://godbolt.org/z/ZZLVD- > > > > > > > > struct ov7670_win_size { > > > > int width; > > > > int height; > > > > }; > > > > struct ov7670_devtype { > > > > struct ov7670_win_size *win_sizes; > > > > unsigned n_win_sizes; > > > > }; > > > > struct ov7670_info { > > > > int min_width; > > > > int min_height; > > > > struct ov7670_devtype devtype; > > > > } a; > > > > int b; > > > > int fn1() { > > > > struct ov7670_info c = a; > > > > int i = 0; > > > > for (; i < c.devtype.n_win_sizes; i++) { > > > > struct ov7670_win_size d = c.devtype.win_sizes[i]; > > > > if (c.min_width && d.width < d.height < c.min_height) > > > > if (b) > > > > return 0; > > > > } > > > > return 2; > > > > } > > > > > > > > $ clang-8 -O2 -fno-omit-frame-pointer -fno-strict-overflow -c ov7670.i > > > > $ objtool check --no-unreachable --uaccess ov7670.o > > > > ov7670.o: warning: objtool: fn1 uses BP as a scratch register > > > > > > Thanks for the report and reduced test case. From the godbolt link, I > > > don't see %rbp, %ebp, %bp, or %bpl being referenced (other that %rbp > > > in the typical epilogue). Am I missing something? Is objtool maybe > > > not reporting the precise function at fault? > > > > I haven't looked, but it could very well be an objtool bug (surprise). > > Actually the reproducer may be wrong. I reduced the test case using > 9.0.0-svn363902-1~exp1+0~20190620001509.2315~1.gbp76e756, > and this contains a link > > testl %ebp, %ebp > > I get the same thing with clang-8, but godbolt.org shows it only > with clang-8 (see https://godbolt.org/z/g1lZO0) , not with trunk.
(Sorry for sending a blank email just now) + Craig and Simon, in case they recall this being a recent fix in LLVM's x86 backend. Sounds like this is fixing in upstream LLVM. Guessing this could result in improper unwinding w/ clang-8, but that's kind of irrelevant for x86 as there's no asm goto (though we don't need CONFIG_JUMP_LABEL in LTS branches :P) -- Thanks, ~Nick Desaulniers