Support for the pseudo-C BPF assembler syntax in GAS

Support for the pseudo-C BPF assembler syntax in GAS

[Jose E. Marchesi]

Just a heads up, we just committed support for the assembly syntax used
by clang to the GNU assembler [1].

Salud!

[1] https://sourceware.org/pipermail/binutils/2023-April/127222.html

Re: Support for the pseudo-C BPF assembler syntax in GAS

[Yonghong Song]

On 4/26/23 10:37 AM, Jose E. Marchesi wrote:
> 
> Just a heads up, we just committed support for the assembly syntax used
> by clang to the GNU assembler [1].

Thanks! Do you which gcc release is expected to contain these changes?

> 
> Salud!
> 
> [1] https://sourceware.org/pipermail/binutils/2023-April/127222.html

Re: Support for the pseudo-C BPF assembler syntax in GAS

[Jose E. Marchesi]

> On 4/26/23 10:37 AM, Jose E. Marchesi wrote:
>> Just a heads up, we just committed support for the assembly syntax
>> used
>> by clang to the GNU assembler [1].
>
> Thanks! Do you which gcc release is expected to contain these changes?

This is the assembler, i.e. binutils.
We don't need to update the compiler.

>> Salud!
>> [1] https://sourceware.org/pipermail/binutils/2023-April/127222.html

Re: Support for the pseudo-C BPF assembler syntax in GAS

[Alexei Starovoitov]

On Wed, Apr 26, 2023 at 12:35 PM Jose E. Marchesi
<jose.marchesi@oracle.com> wrote:
>
>
> > On 4/26/23 10:37 AM, Jose E. Marchesi wrote:
> >> Just a heads up, we just committed support for the assembly syntax
> >> used
> >> by clang to the GNU assembler [1].
> >
> > Thanks! Do you which gcc release is expected to contain these changes?
>
> This is the assembler, i.e. binutils.
> We don't need to update the compiler.
>
> >> Salud!
> >> [1] https://sourceware.org/pipermail/binutils/2023-April/127222.html

This is awesome!
We recently converted tens of thousands of lines of bpf asm from macros
to inline asm in C.
See tools/testing/selftests/bpf/progs/verifier_*.c
I wonder how gas-bpf can deal with that.
We had to fix several inline asm issues in clang to get to this point
and probably more to come.

Re: Support for the pseudo-C BPF assembler syntax in GAS

[Jose E. Marchesi]

Odd.  I replied to this yesterday, but somehow it wasn't sent.

> On Wed, Apr 26, 2023 at 12:35 PM Jose E. Marchesi
> <jose.marchesi@oracle.com> wrote:
>>
>>
>> > On 4/26/23 10:37 AM, Jose E. Marchesi wrote:
>> >> Just a heads up, we just committed support for the assembly syntax
>> >> used
>> >> by clang to the GNU assembler [1].
>> >
>> > Thanks! Do you which gcc release is expected to contain these changes?
>>
>> This is the assembler, i.e. binutils.
>> We don't need to update the compiler.
>>
>> >> Salud!
>> >> [1] https://sourceware.org/pipermail/binutils/2023-April/127222.html
>
> This is awesome!
> We recently converted tens of thousands of lines of bpf asm from macros
> to inline asm in C.
> See tools/testing/selftests/bpf/progs/verifier_*.c
> I wonder how gas-bpf can deal with that.

Inline assembly shall work.

> We had to fix several inline asm issues in clang to get to this point
> and probably more to come.

We will give these tests a try and fix problems as we find them :)

We actually came with some ambiguities, undefined stuff, and other
issues with the syntax while doing the implementation.  We hope to
discuss some of that during the LSF/MM/BPF next week, so we can
consolidate the language in both toolchains.

Speaking of which, we are preparing the material for the "compiled BPF"
activity during LSF/MM/BPF.  I think the BPF track hasn't been scheduled
yet, but how much time will we have to discuss about the topic?

Re: Support for the pseudo-C BPF assembler syntax in GAS

[Eduard Zingerman]

On Thu, 2023-04-27 at 12:14 +0200, Jose E. Marchesi wrote:
> Odd.  I replied to this yesterday, but somehow it wasn't sent.
> 
> > On Wed, Apr 26, 2023 at 12:35 PM Jose E. Marchesi
> > <jose.marchesi@oracle.com> wrote:
> > > 
> > > 
> > > > On 4/26/23 10:37 AM, Jose E. Marchesi wrote:
> > > > > Just a heads up, we just committed support for the assembly syntax
> > > > > used
> > > > > by clang to the GNU assembler [1].
> > > > 
> > > > Thanks! Do you which gcc release is expected to contain these changes?
> > > 
> > > This is the assembler, i.e. binutils.
> > > We don't need to update the compiler.
> > > 
> > > > > Salud!
> > > > > [1] https://sourceware.org/pipermail/binutils/2023-April/127222.html
> > 
> > This is awesome!
> > We recently converted tens of thousands of lines of bpf asm from macros
> > to inline asm in C.
> > See tools/testing/selftests/bpf/progs/verifier_*.c
> > I wonder how gas-bpf can deal with that.
> 
> Inline assembly shall work.

There is also an LLVM testcase [1] where most of the instructions are covered,
but you probably have something similar.

Just of the curiosity, is the state machine generated by some tool or
is it "pen and paper" exercise?

[1] https://github.com/llvm/llvm-project/blob/main/llvm/test/CodeGen/BPF/assembler-disassembler.s

> 
> > We had to fix several inline asm issues in clang to get to this point
> > and probably more to come.
> 
> We will give these tests a try and fix problems as we find them :)
> 
> We actually came with some ambiguities, undefined stuff, and other
> issues with the syntax while doing the implementation.  We hope to
> discuss some of that during the LSF/MM/BPF next week, so we can
> consolidate the language in both toolchains.
> 
> Speaking of which, we are preparing the material for the "compiled BPF"
> activity during LSF/MM/BPF.  I think the BPF track hasn't been scheduled
> yet, but how much time will we have to discuss about the topic?

Re: Support for the pseudo-C BPF assembler syntax in GAS

[Alexei Starovoitov]

On Thu, Apr 27, 2023 at 3:14 AM Jose E. Marchesi
<jose.marchesi@oracle.com> wrote:
>
>
> Odd.  I replied to this yesterday, but somehow it wasn't sent.
>
> > On Wed, Apr 26, 2023 at 12:35 PM Jose E. Marchesi
> > <jose.marchesi@oracle.com> wrote:
> >>
> >>
> >> > On 4/26/23 10:37 AM, Jose E. Marchesi wrote:
> >> >> Just a heads up, we just committed support for the assembly syntax
> >> >> used
> >> >> by clang to the GNU assembler [1].
> >> >
> >> > Thanks! Do you which gcc release is expected to contain these changes?
> >>
> >> This is the assembler, i.e. binutils.
> >> We don't need to update the compiler.
> >>
> >> >> Salud!
> >> >> [1] https://sourceware.org/pipermail/binutils/2023-April/127222.html
> >
> > This is awesome!
> > We recently converted tens of thousands of lines of bpf asm from macros
> > to inline asm in C.
> > See tools/testing/selftests/bpf/progs/verifier_*.c
> > I wonder how gas-bpf can deal with that.
>
> Inline assembly shall work.
>
> > We had to fix several inline asm issues in clang to get to this point
> > and probably more to come.
>
> We will give these tests a try and fix problems as we find them :)
>
> We actually came with some ambiguities, undefined stuff, and other
> issues with the syntax while doing the implementation.  We hope to
> discuss some of that during the LSF/MM/BPF next week, so we can
> consolidate the language in both toolchains.
>
> Speaking of which, we are preparing the material for the "compiled BPF"
> activity during LSF/MM/BPF.  I think the BPF track hasn't been scheduled
> yet, but how much time will we have to discuss about the topic?

Awesome. I'd love to participate.

Martin, Daniel,
What is the schedule for bpf track ?

Re: Support for the pseudo-C BPF assembler syntax in GAS

[Jose E. Marchesi]

> On Thu, 2023-04-27 at 12:14 +0200, Jose E. Marchesi wrote:
>> Odd.  I replied to this yesterday, but somehow it wasn't sent.
>> 
>> > On Wed, Apr 26, 2023 at 12:35 PM Jose E. Marchesi
>> > <jose.marchesi@oracle.com> wrote:
>> > > 
>> > > 
>> > > > On 4/26/23 10:37 AM, Jose E. Marchesi wrote:
>> > > > > Just a heads up, we just committed support for the assembly syntax
>> > > > > used
>> > > > > by clang to the GNU assembler [1].
>> > > > 
>> > > > Thanks! Do you which gcc release is expected to contain these changes?
>> > > 
>> > > This is the assembler, i.e. binutils.
>> > > We don't need to update the compiler.
>> > > 
>> > > > > Salud!
>> > > > > [1] https://sourceware.org/pipermail/binutils/2023-April/127222.html
>> > 
>> > This is awesome!
>> > We recently converted tens of thousands of lines of bpf asm from macros
>> > to inline asm in C.
>> > See tools/testing/selftests/bpf/progs/verifier_*.c
>> > I wonder how gas-bpf can deal with that.
>> 
>> Inline assembly shall work.
>
> There is also an LLVM testcase [1] where most of the instructions are covered,
> but you probably have something similar.

Yes we have extensive instruction testing in the assembler.

> Just of the curiosity, is the state machine generated by some tool or
> is it "pen and paper" exercise?

It is the later :)

But I plan to turn that function into a recursive-descend, for
maintainability.

> [1] https://github.com/llvm/llvm-project/blob/main/llvm/test/CodeGen/BPF/assembler-disassembler.s
>
>> 
>> > We had to fix several inline asm issues in clang to get to this point
>> > and probably more to come.
>> 
>> We will give these tests a try and fix problems as we find them :)
>> 
>> We actually came with some ambiguities, undefined stuff, and other
>> issues with the syntax while doing the implementation.  We hope to
>> discuss some of that during the LSF/MM/BPF next week, so we can
>> consolidate the language in both toolchains.
>> 
>> Speaking of which, we are preparing the material for the "compiled BPF"
>> activity during LSF/MM/BPF.  I think the BPF track hasn't been scheduled
>> yet, but how much time will we have to discuss about the topic?

Re: Support for the pseudo-C BPF assembler syntax in GAS

[Jose E. Marchesi]

>> On 4/26/23 10:37 AM, Jose E. Marchesi wrote:
>>> Just a heads up, we just committed support for the assembly syntax
>>> used
>>> by clang to the GNU assembler [1].
>>
>> Thanks! Do you which gcc release is expected to contain these changes?
>
> This is the assembler, i.e. binutils.
> We don't need to update the compiler.

Turns out we do indeed have to update GCC.  Otherwise non-trivial inline
asm ends in mixed syntaxes within an instruction (like r2 = %r3).  We
are looking into this.

Oh well.

>
>>> Salud!
>>> [1] https://sourceware.org/pipermail/binutils/2023-April/127222.html