Re: [PATCH 01/15] objtool: Find a destination for jumps beyond the section end

[Sami Tolvanen]

On Tue, Apr 20, 2021 at 11:14 AM Josh Poimboeuf <jpoimboe@xxxxxxxxxx> 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

Sami