[Bug c/107971] New: linking an assembler object creates an executable stack

[Bug c/107971] New: linking an assembler object creates an executable stack

[contact@alexander-pick.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107971

            Bug ID: 107971
           Summary: linking an assembler object creates an executable
                    stack
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: contact@alexander-pick.com
  Target Milestone: ---

Created attachment 54011
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54011&action=edit
simple testcase for the issue

I encountered a strange behavior with gcc and linking an assembler object.
Doing so will create a binary with executable stack. A testcase is attached.

The code will compile a very simple assembler file as an object and link it to
an object compiled from C. The binary will have an executable stack by default
which isn't that great from a security point of view. Setting "-z noexecstack"
as a workaround is the only way to prevent this.

31:   STACK off    0x0000000000000000 vaddr 0x0000000000000000 paddr
0x0000000000000000 align 2**4
32-         filesz 0x0000000000000000 memsz 0x0000000000000000 flags rwx

[Bug c/107971] linking an assembler object creates an executable stack

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107971

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |WONTFIX
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Gcc just invokes the assembly. The problem is legacy assembly code might still
use an executable stack.
Best way to fix this is for you to add the option. There is nothing gcc is
going to change to be different here.
Also the assembler is not part of gcc. Most likely you are using gnu binutils.

[Bug c/107971] linking an assembler object creates an executable stack

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107971

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
You can use the assembler note to communicate to the linker that the assembly
code does not use executable stack. This is all documented in the linker
documentation and is not part of gcc documentation.

[Bug c/107971] linking an assembler object creates an executable stack

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107971

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
https://sourceware.org/binutils/docs-2.39/ld/Options.html#index-_002d_002dwarn_002dexecstack

```
Note: ELF format input files specify that they need an executable stack by
having a .note.GNU-stack section with the executable bit set in its section
flags. They can specify that they do not need an executable stack by having
that section, but without the executable flag bit set. If an input file does
not have a .note.GNU-stack section present then the default behaviour is target
specific. For some targets, then absence of such a section implies that an
executable stack is required. ****This is often a problem for hand crafted
assembler files.****
```

Added emphasize is mine.

[Bug c/107971] linking an assembler object creates an executable stack

[contact@alexander-pick.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107971

--- Comment #4 from Alexander Pick <contact@alexander-pick.com> ---
Thanks a lot for the explanation. Do you think that it is worth reporting it to
binutils as the text in the link also says that there should be a warning
unless the option to have an executable stack is explicitly specified? In the
test case there is no such warning. I also tried to link the objects with LD
directly - same result and also no warning.

[Bug c/107971] linking an assembler object creates an executable stack

[amonakov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107971

Alexander Monakov <amonakov at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |amonakov at gcc dot gnu.org

--- Comment #5 from Alexander Monakov <amonakov at gcc dot gnu.org> ---
The warning is new in binutils-2.39 (the latest release at this time), perhaps
your linker is older.