On Mon, Mar 27, 2023 at 9:35 AM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Sun, Mar 26, 2023 at 8:57 PM Alexei Starovoitov
> <alexei.starovoitov@xxxxxxxxx> wrote:
> >
> > On Sun, Mar 26, 2023 at 8:16 PM Andrii Nakryiko
> > <andrii.nakryiko@xxxxxxxxx> wrote:
> > >
> > > On Sat, Mar 25, 2023 at 6:19 PM Alexei Starovoitov
> > > <alexei.starovoitov@xxxxxxxxx> wrote:
> > > >
> > > > On Sat, Mar 25, 2023 at 9:16 AM Stanislav Fomichev <sdf@xxxxxxxxxx> wrote:
> > > > >
> > > > > >
> > > > > > It was my understanding from the RFC feedback that this "lighter" way
> > > > > > is preferable and we already have some tests written like that.
> > > > > > Don't have a strong opinion on this topic.
> > > > >
> > > > > Ack, I'm obviously losing a bunch of context here :-(
> > > > > I like coalescing better, but if the original suggestion was to use
> > > > > this lighter way, I'll keep that in mind while reviewing.
> > > >
> > > > I still prefer the clean look of the tests, so I've applied this set.
> > > >
> > > > But I'm not going to insist that this is the only style developers
> > > > should use moving forward.
> > > > Whoever prefers "" style can use it in the future tests.
> > >
> > > Great, because I found out in practice that inability to add comments
> > > to the manually written asm code is a pretty big limitation.
> >
> > What do you mean by "inability" ?
> > The comments can be added. See verifier_and.c
> > r0 &= 0xFFFF1234; \
> > /* Upper bits are unknown but AND above masks out 1 zero'ing
> > lower bits */\
> > if w0 < 1 goto l0_%=; \
>
> My bad. I remembered that there were problems with comments in Eduards
> previous revision and concluded that they don't work in this
> "\-delimited mode". Especially that online documentation for GCC or
> Clang didn't explicitly say that they support /* */ comments in asm
> blocks (as far as I could google that).
>
> So now I know it's possible, thanks. I still find it very tedious to
> do manually, so I appreciate the flexibility in allowing to do
> ""-delimited style for new programs.
>
> Just to explain where I'm coming from. I took one asm program I have
> locally and converted it to a new style. It was tedious with all the
> tab alignment. Then I realized that one comment block uses too long
> lines and wanted to use vim to reformat them, and that doesn't work
> with those '\' delimiters at the end (I didn't have such a problem
> with the original style). So that turned into more tedious work. So
> for something that needs iteration and adjustments, ""-delimited style
> gives more flexibility. See below for reference.
>
> '#' comments are dangerous, btw, they silently ignore everything till
> the very end of asm block. No warning or error, just wrong and
> incomplete asm is generated, unfortunately.
>
>
> SEC("?raw_tp")
> __failure __log_level(2)
> __msg("XXX")
> __naked int subprog_result_precise(void)
> {
> asm volatile (
> "r6 = 3;"
> /* pass r6 through r1 into subprog to get it back as r0;
> * this whole chain will have to be marked as precise later
> */
> "r1 = r6;"
> "call identity_subprog;"
> /* now use subprog's returned value (which is a
> * r6 -> r1 -> r0 chain), as index into vals array, forcing
> * all of that to be known precisely
> */
> "r0 *= 4;"
> "r1 = %[vals];"
> "r1 += r0;"
> /* here r0->r1->r6 chain is forced to be precise and has to be
> * propagated back to the beginning, including through the
> * subprog call
> */
> "r0 = *(u32 *)(r1 + 0);"
> "exit;"
> :
> : __imm_ptr(vals)
> : __clobber_common, "r6"
> );
> }
>
> SEC("?raw_tp")
> __failure __log_level(2)
> __msg("XXX")
> __naked int subprog_result_precise2(void)
> {
> asm volatile ("
> \
> r6 = 3;
> \
> /* pass r6 through r1 into subprog to get it back as
> r0; \
> * this whole chain will have to be marked as precise
> later \
> */
> \
> r1 = r6;
> \
> call identity_subprog;
> \
> /* now use subprog's returned value (which is a
> \
> * r6 -> r1 -> r0 chain), as index into vals array,
> forcing \
> * all of that to be known precisely
> \
> */
> \
> r0 *= 4;
> \
> r1 = %[vals];
> \
> r1 += r0;
> \
> /* here r0->r1->r6 chain is forced to be precise and
> has to be \
> * propagated back to the beginning, including through
> the \
> * subprog call
> \
> */
> \
> r0 = *(u32 *)(r1 + 0);
> \
> exit;
> \
Great, Gmail doesn't like this style as well :( Sorry for the visual noise.
> "
> :
> : __imm_ptr(vals)
> : __clobber_common, "r6"
> );
> }
