lkml.org 
[lkml]   [2021]   [Apr]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 01/15] objtool: Find a destination for jumps beyond the section end
On Tue, Apr 20, 2021 at 01:25:43PM -0700, Sami Tolvanen wrote:
> On Tue, Apr 20, 2021 at 11:14 AM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> >
> > On Fri, Apr 16, 2021 at 01:38:30PM -0700, Sami Tolvanen wrote:
> > > With -ffunction-sections, Clang can generate a jump beyond the end of
> > > a section when the section ends in an unreachable instruction.
> >
> > Why? Can you show an example?
>
> Here's the warning I'm seeing when building allyesconfig + CFI:
>
> vmlinux.o: warning: objtool:
> rockchip_spi_transfer_one.f088382d97b74759d70e27e891fe8f1c()+0x149:
> can't find jump dest instruction at
> .text.rockchip_spi_transfer_one.f088382d97b74759d70e27e891fe8f1c+0x7dc
>
> $ objdump -d -r -j
> .text.rockchip_spi_transfer_one.f088382d97b74759d70e27e891fe8f1c
> vmlinux.o
> 0000000000000000 <rockchip_spi_transfer_one.f088382d97b74759d70e27e891fe8f1c>:
> ...
> 149: 0f 85 8d 06 00 00 jne 7dc <.compoundliteral.4>
> ...
> 7d7: e8 00 00 00 00 callq 7dc <.compoundliteral.4>
> 7d8: R_X86_64_PLT32 __stack_chk_fail-0x4

Instead of silencing the warning by faking the jump destination, I'd
rather improve the warning to something like

"warning: rockchip_spi_transfer_one() falls through to the next function"

which is what we normally do in this type of situation.

It may be caused by UB, or a compiler bug, but either way we should
figure out the root cause.

--
Josh

\
 
 \ /
  Last update: 2021-04-21 00:57    [W:0.245 / U:0.624 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site