On Sun, Mar 14, 2021 at 10:29 PM Alexander Lochmann
<info@xxxxxxxxxxxxxxxxxxxxx> wrote:
> On 12.02.21 13:54, Dmitry Vyukov wrote:
> >
> > I think we could make KCOV_IN_CTXSW sign bit and then express the check as:
> >
> > void foo2(unsigned mode) {
> > if (((int)(mode & 0x8000000a)) > 0)
> > foo();
> > }
> >
> > 0000000000000020 <foo2>:
> > 20: 81 e7 0a 00 00 80 and $0x8000000a,%edi
> > 26: 7f 08 jg 30 <foo2+0x10>
> > 28: c3 retq
> >
> So ((int)(mode & (KCOV_IN_CTXSW | needed_mode))) > 0?
Frankly I lost all context now. If it results in optimal code, then, yes.
> >> }
> >>
> >> static notrace unsigned long canonicalize_ip(unsigned long ip)
> >> @@ -191,18 +192,26 @@ void notrace __sanitizer_cov_trace_pc(void)
> >> struct task_struct *t;
> >> unsigned long *area;
> >> unsigned long ip = canonicalize_ip(_RET_IP_);
> >> - unsigned long pos;
> >> + unsigned long pos, idx;
> >>
> >> t = current;
> >> - if (!check_kcov_mode(KCOV_MODE_TRACE_PC, t))
> >> + if (!check_kcov_mode(KCOV_MODE_TRACE_PC | KCOV_MODE_UNIQUE_PC, t))
> >> return;
> >>
> >> area = t->kcov_area;
> >> - /* The first 64-bit word is the number of subsequent PCs. */
> >> - pos = READ_ONCE(area[0]) + 1;
> >> - if (likely(pos < t->kcov_size)) {
> >> - area[pos] = ip;
> >> - WRITE_ONCE(area[0], pos);
> >> + if (likely(t->kcov_mode == KCOV_MODE_TRACE_PC)) {
> >
> > Does this introduce an additional real of t->kcov_mode?
> > If yes, please reuse the value read in check_kcov_mode.
> Okay. How do I get that value from check_kcov_mode() to the caller?
> Shall I add an additional parameter to check_kcov_mode()?
Yes, I would try to add an additional pointer parameter for mode. I
think after inlining the compiler should be able to regestrize it.
> >> + /* The first 64-bit word is the number of subsequent PCs. */
> >> + pos = READ_ONCE(area[0]) + 1;
> >> + if (likely(pos < t->kcov_size)) {
> >> + area[pos] = ip;
> >> + WRITE_ONCE(area[0], pos);
> >> + }
> >> + } else {
> >> + idx = (ip - canonicalize_ip((unsigned long)&_stext)) / 4;
> >> + pos = idx % BITS_PER_LONG;
> >> + idx /= BITS_PER_LONG;
> >> + if (likely(idx < t->kcov_size))
> >> + WRITE_ONCE(area[idx], READ_ONCE(area[idx]) | 1L << pos);
> >> }
> >> }
> >> EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
> >> @@ -474,6 +483,7 @@ static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
> >> goto exit;
> >> }
> >> if (!kcov->area) {
> >> + kcov_debug("mmap(): Allocating 0x%lx bytes\n", size);
> >> kcov->area = area;
> >> vma->vm_flags |= VM_DONTEXPAND;
> >> spin_unlock_irqrestore(&kcov->lock, flags);
> >> @@ -515,6 +525,8 @@ static int kcov_get_mode(unsigned long arg)
> >> {
> >> if (arg == KCOV_TRACE_PC)
> >> return KCOV_MODE_TRACE_PC;
> >> + else if (arg == KCOV_UNIQUE_PC)
> >> + return KCOV_MODE_UNIQUE_PC;
> >
> > As far as I understand, users can first do KCOV_INIT_UNIQUE and then
> > enable KCOV_TRACE_PC, or vice versa.
> > It looks somewhat strange. Is it intentional?
> I'll fix that.
> It's not possible to
> > specify buffer size for KCOV_INIT_UNIQUE, so most likely the buffer
> > will be either too large or too small for a trace.
> No, the buffer will be calculated by KCOV_INIT_UNIQUE based on the size
> of the text segment.
Yes, which will be either too large or too small for KCOV_TRACE_PC
enabled later.
> - Alex
>
> --
> Alexander Lochmann PGP key: 0xBC3EF6FD
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