lkml.org 
[lkml]   [2019]   [Aug]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: objtool warning "uses BP as a scratch register" with clang-9
    On Tue, Aug 27, 2019 at 12:22 PM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
    >
    > On Tue, Aug 27, 2019 at 09:00:52PM +0200, Arnd Bergmann wrote:
    > > On Tue, Aug 27, 2019 at 5:00 PM Ilie Halip <ilie.halip@gmail.com> wrote:
    > > >
    > > > > > $ clang-9 -c crc32.i -O2 ; objtool check crc32.o
    > > > > > crc32.o: warning: objtool: fn1 uses BP as a scratch register
    > > >
    > > > Yes, I see it too. https://godbolt.org/z/N56HW1
    > > >
    > > > > Do you still see this warning with -fno-omit-frame-pointer (assuming
    > > > > clang has that option)?
    > > >
    > > > Using this makes the warning go away. Running objtool with --no-fp
    > > > also gets rid of it.
    > >
    > > I still see the warning after adding back the -fno-omit-frame-pointer
    > > in my reduced test case:
    > >
    > > $ clang-9 -c crc32.i -Werror -Wno-address-of-packed-member -Wall
    > > -Wno-pointer-sign -Wno-unused-value -Wno-constant-logical-operand -O2
    > > -Wno-unused -fno-omit-frame-pointer
    > > $ objtool check crc32.o
    > > crc32.o: warning: objtool: fn1 uses BP as a scratch register
    >
    > This warning most likely means that clang is clobbering RBP in leaf
    > functions. With -fno-omit-frame-pointer, leaf functions don't need to
    > set up the frame pointer, but they at least need to leave RBP untouched,
    > so that an interrupts/exceptions can unwind through the function.

    It sounds like clang has `-mno-omit-leaf-frame-pointer` (via
    https://bugs.llvm.org/show_bug.cgi?id=43128#c6). Arnd, can you give
    that a shot?
    --
    Thanks,
    ~Nick Desaulniers

    \
     
     \ /
      Last update: 2019-08-29 00:14    [W:4.606 / U:0.012 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site