Messages in this thread | | | Date | Wed, 28 Mar 2018 11:50:09 -0700 | From | Matthias Kaehlcke <> | Subject | Re: [PATCH] debugfs: Check return value of debugfs_real_fops() for NULL |
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El Wed, Mar 28, 2018 at 08:19:36PM +0200 Greg Kroah-Hartman ha dit:
> On Wed, Mar 28, 2018 at 11:14:56AM -0700, Matthias Kaehlcke wrote: > > El Wed, Mar 28, 2018 at 08:05:56PM +0200 Greg Kroah-Hartman ha dit: > > > > > > > > A: Because it messes up the order in which people normally read text. > > > Q: Why is top-posting such a bad thing? > > > A: Top-posting. > > > Q: What is the most annoying thing in e-mail? > > > > > > A: No. > > > Q: Should I include quotations after my reply? > > > > > > http://daringfireball.net/2007/07/on_top > > > > > > On Wed, Mar 28, 2018 at 07:47:53AM -0700, Manoj Gupta wrote: > > > > Please note that there is nothing wrong in the generated code, just > > > > that it confuses objtool. > > > > > > Then fix the tool, the C code is correct :) > > > > > > > Clang has simply omitted the statement where NULL is returned since > > > > the pointer was always dereferenced post inlining. > > > > > > Then tell clang not to do that, like we tell gcc not to do that as that > > > is a foolish thing for a compiler to do when building the kernel. > > > > Thanks all for your input, we'll try to get > > -fno-delete-null-pointer-checks or a similar flag to be added to > > clang. > > Wait, clang does not have that?
Nope, clang doesn't currently have such a flag.
> That's crazy, how has this not been hit yet when building the > kernel?
IIRC this patch was needed to work around the lack of the flag:
commit beaec533fc2701a28a4d667f67c9f59c6e4e0d13 Author: Alexander Potapenko <glider@google.com> Date: Wed Jul 19 20:27:30 2017 +0200
llist: clang: introduce member_address_is_nonnull()
Currently llist_for_each_entry() and llist_for_each_entry_safe() iterate until &pos->member != NULL. But when building the kernel with Clang, the compiler assumes &pos->member cannot be NULL if the member's offset is greater than 0 (which would be equivalent to the object being non-contiguous in memory). Therefore the loop condition is always true, and the loops become infinite.
To work around this, introduce the member_address_is_nonnull() macro, which casts object pointer to uintptr_t, thus letting the member pointer to be NULL.
Signed-off-by: Alexander Potapenko <glider@google.com> Tested-by: Sodagudi Prasad <psodagud@codeaurora.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Other than that I am not aware of any known issues.
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