riscv: align stack before calling _dl_init [BZ #28703]
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Commit Message
Align the stack pointer to 128 bits during the call to _dl_init() as
specified by the RISC-V ABI [1]. This fixes the elf/tst-align2 test.
Fixes bug 28703.
[1] https://github.com/riscv-non-isa/riscv-elf-psabi-doc
---
sysdeps/riscv/dl-machine.h | 6 ++++++
1 file changed, 6 insertions(+)
Comments
Even though sp should be sufficiently aligned upon program entry, the
_dl_skip_args jig can misalign the stack. So, LGTM.
On Wed, Dec 15, 2021 at 3:12 PM Aurelien Jarno <aurelien@aurel32.net> wrote:
>
> Align the stack pointer to 128 bits during the call to _dl_init() as
> specified by the RISC-V ABI [1]. This fixes the elf/tst-align2 test.
>
> Fixes bug 28703.
>
> [1] https://github.com/riscv-non-isa/riscv-elf-psabi-doc
> ---
> sysdeps/riscv/dl-machine.h | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/sysdeps/riscv/dl-machine.h b/sysdeps/riscv/dl-machine.h
> index ce2b3c3875..f457a41c70 100644
> --- a/sysdeps/riscv/dl-machine.h
> +++ b/sysdeps/riscv/dl-machine.h
> @@ -125,8 +125,14 @@ elf_machine_dynamic (void)
> sll a3, a1, " STRINGXP (PTRLOG) "\n\
> add a3, a3, a2\n\
> add a3, a3, " STRINGXP (SZREG) "\n\
> + # Stash the stack pointer in s1.\n\
> + mv s1, sp\n\
> + # Align stack to 128 bits for the _dl_init call.\n\
> + andi sp, sp,-16\n\
> # Call the function to run the initializers.\n\
> jal _dl_init\n\
> + # Restore the stack pointer for _start.\n\
> + mv sp, s1\n\
> # Pass our finalizer function to _start.\n\
> lla a0, _dl_fini\n\
> # Jump to the user entry point.\n\
> --
> 2.33.0
>
* Aurelien Jarno:
> + # Align stack to 128 bits for the _dl_init call.\n\
> + andi sp, sp,-16\n\
> # Call the function to run the initializers.\n\
> jal _dl_init\n\
How is that extra alignment observable to user code?
Thanks,
Florian
On 2021-12-16 07:51, Florian Weimer wrote:
> * Aurelien Jarno:
>
> > + # Align stack to 128 bits for the _dl_init call.\n\
> > + andi sp, sp,-16\n\
> > # Call the function to run the initializers.\n\
> > jal _dl_init\n\
>
> How is that extra alignment observable to user code?
This extra alignment is visible to the constructors, called from
_dl_init. This is how this is tested in elf/tst-align2.c, however the
issue wasn't detected due to BZ #27901.
On Dez 16 2021, Aurelien Jarno wrote:
> diff --git a/sysdeps/riscv/dl-machine.h b/sysdeps/riscv/dl-machine.h
> index ce2b3c3875..f457a41c70 100644
> --- a/sysdeps/riscv/dl-machine.h
> +++ b/sysdeps/riscv/dl-machine.h
> @@ -125,8 +125,14 @@ elf_machine_dynamic (void)
> sll a3, a1, " STRINGXP (PTRLOG) "\n\
> add a3, a3, a2\n\
> add a3, a3, " STRINGXP (SZREG) "\n\
> + # Stash the stack pointer in s1.\n\
> + mv s1, sp\n\
> + # Align stack to 128 bits for the _dl_init call.\n\
> + andi sp, sp,-16\n\
> # Call the function to run the initializers.\n\
> jal _dl_init\n\
> + # Restore the stack pointer for _start.\n\
> + mv sp, s1\n\
> # Pass our finalizer function to _start.\n\
> lla a0, _dl_fini\n\
> # Jump to the user entry point.\n\
Shouldn't the adjustment already be made after the _dl_skip_args fixup,
permanently?
On 2021-12-16 09:48, Andreas Schwab wrote:
> On Dez 16 2021, Aurelien Jarno wrote:
>
> > diff --git a/sysdeps/riscv/dl-machine.h b/sysdeps/riscv/dl-machine.h
> > index ce2b3c3875..f457a41c70 100644
> > --- a/sysdeps/riscv/dl-machine.h
> > +++ b/sysdeps/riscv/dl-machine.h
> > @@ -125,8 +125,14 @@ elf_machine_dynamic (void)
> > sll a3, a1, " STRINGXP (PTRLOG) "\n\
> > add a3, a3, a2\n\
> > add a3, a3, " STRINGXP (SZREG) "\n\
> > + # Stash the stack pointer in s1.\n\
> > + mv s1, sp\n\
> > + # Align stack to 128 bits for the _dl_init call.\n\
> > + andi sp, sp,-16\n\
> > # Call the function to run the initializers.\n\
> > jal _dl_init\n\
> > + # Restore the stack pointer for _start.\n\
> > + mv sp, s1\n\
> > # Pass our finalizer function to _start.\n\
> > lla a0, _dl_fini\n\
> > # Jump to the user entry point.\n\
>
> Shouldn't the adjustment already be made after the _dl_skip_args fixup,
> permanently?
I have basically followed what is done on i386, mips or x86_64. I can
give a try to keep the alignment permanent and see if things still work.
* Aurelien Jarno:
> On 2021-12-16 07:51, Florian Weimer wrote:
>> * Aurelien Jarno:
>>
>> > + # Align stack to 128 bits for the _dl_init call.\n\
>> > + andi sp, sp,-16\n\
>> > # Call the function to run the initializers.\n\
>> > jal _dl_init\n\
>>
>> How is that extra alignment observable to user code?
>
> This extra alignment is visible to the constructors, called from
> _dl_init. This is how this is tested in elf/tst-align2.c, however the
> issue wasn't detected due to BZ #27901.
Ah, sorry, I misread “128 bits” as “128 bytes”. 16-byte alignment will
be preserved by the compiler.
Thanks,
Florian
On Dez 16 2021, Aurelien Jarno wrote:
> On 2021-12-16 09:48, Andreas Schwab wrote:
>> On Dez 16 2021, Aurelien Jarno wrote:
>>
>> > diff --git a/sysdeps/riscv/dl-machine.h b/sysdeps/riscv/dl-machine.h
>> > index ce2b3c3875..f457a41c70 100644
>> > --- a/sysdeps/riscv/dl-machine.h
>> > +++ b/sysdeps/riscv/dl-machine.h
>> > @@ -125,8 +125,14 @@ elf_machine_dynamic (void)
>> > sll a3, a1, " STRINGXP (PTRLOG) "\n\
>> > add a3, a3, a2\n\
>> > add a3, a3, " STRINGXP (SZREG) "\n\
>> > + # Stash the stack pointer in s1.\n\
>> > + mv s1, sp\n\
>> > + # Align stack to 128 bits for the _dl_init call.\n\
>> > + andi sp, sp,-16\n\
>> > # Call the function to run the initializers.\n\
>> > jal _dl_init\n\
>> > + # Restore the stack pointer for _start.\n\
>> > + mv sp, s1\n\
>> > # Pass our finalizer function to _start.\n\
>> > lla a0, _dl_fini\n\
>> > # Jump to the user entry point.\n\
>>
>> Shouldn't the adjustment already be made after the _dl_skip_args fixup,
>> permanently?
>
> I have basically followed what is done on i386, mips or x86_64. I can
> give a try to keep the alignment permanent and see if things still work.
It looks like your version is ok, since _start is doing its own
alignment (and it needs sp to point to argc).
On 2021-12-16 11:42, Florian Weimer via Libc-alpha wrote:
> * Aurelien Jarno:
>
> > On 2021-12-16 07:51, Florian Weimer wrote:
> >> * Aurelien Jarno:
> >>
> >> > + # Align stack to 128 bits for the _dl_init call.\n\
> >> > + andi sp, sp,-16\n\
> >> > # Call the function to run the initializers.\n\
> >> > jal _dl_init\n\
> >>
> >> How is that extra alignment observable to user code?
> >
> > This extra alignment is visible to the constructors, called from
> > _dl_init. This is how this is tested in elf/tst-align2.c, however the
> > issue wasn't detected due to BZ #27901.
>
> Ah, sorry, I misread “128 bits” as “128 bytes”. 16-byte alignment will
> be preserved by the compiler.
I agree that's a bit unusual to use bits instead of bytes there, but I
used the same terminology as in the RISC-V ABI.
@@ -125,8 +125,14 @@ elf_machine_dynamic (void)
sll a3, a1, " STRINGXP (PTRLOG) "\n\
add a3, a3, a2\n\
add a3, a3, " STRINGXP (SZREG) "\n\
+ # Stash the stack pointer in s1.\n\
+ mv s1, sp\n\
+ # Align stack to 128 bits for the _dl_init call.\n\
+ andi sp, sp,-16\n\
# Call the function to run the initializers.\n\
jal _dl_init\n\
+ # Restore the stack pointer for _start.\n\
+ mv sp, s1\n\
# Pass our finalizer function to _start.\n\
lla a0, _dl_fini\n\
# Jump to the user entry point.\n\