linux-kernel - Re: [PATCH] rdma/siw: Use proper enumerated type in map_cqe

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Date:   Mon, 26 Aug 2019 16:38:29 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Bernard Metzler <BMT@...ich.ibm.com>,
        Doug Ledford <dledford@...hat.com>, linux-rdma@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] rdma/siw: Use proper enumerated type in map_cqe_status

On Mon, Aug 26, 2019 at 12:42:28PM -0300, Jason Gunthorpe wrote:
> On Mon, Aug 26, 2019 at 08:38:00AM -0700, Nathan Chancellor wrote:
> > On Fri, Aug 23, 2019 at 11:24:27AM -0300, Jason Gunthorpe wrote:
> > > The latest clang-9 packages from apt.llvm.org do seem to build the
> > > kernel, I get one puzzling warning under RDMA:
> > > 
> > > drivers/infiniband/hw/hfi1/platform.o: warning: objtool: tune_serdes()+0x1f4: can't find jump dest instruction at .text+0x118a
> > 
> > Any particular config that I should use to easily reproduce this?
> 
> Sure, attached. With the clang-9 build for Bionic

This is reproducible with the kernel config attached and a tip of tree
build of LLVM.

$ make -j$(nproc) CC=clang O=out clean olddefconfig drivers/infiniband/hw/hfi1/platform.o
...
  CC      drivers/infiniband/hw/hfi1/platform.o
drivers/infiniband/hw/hfi1/platform.o: warning: objtool: tune_serdes()+0x1f4: can't find jump dest instruction at .text+0x117a

I ran creduce on that file and it spits out:

a() {
  char *b = a;
  switch (b[7] & 240 >> 4) {
  case 10 ... 11:
    c();
  case 0 ... 9:
  case 12:
  case 14:
    d();
  case 13:
  case 15:;
  }
}

to simply reproduce the warning. The original preprocessed file +
interestingness test are available here:

https://github.com/nathanchance/creduce-files/tree/4e252c0ca19742c90be1445e6c722a43ae561144/rdma-objtool

Looks like that comes from tune_qsfp, which gets inlined into
tune_serdes but I am far from an objtool expert so I am not
really sure what kind of issues I am looking for. Adding Josh
and Peter for a little more visibility.

Here is the original .o file as well:

https://github.com/nathanchance/creduce-files/raw/4e252c0ca19742c90be1445e6c722a43ae561144/rdma-objtool/platform.o.orig

Cheers,
Nathan