SPARC - passing argument from C++ to Rust issue

[psumbera]

This was originally reported as Firefox issue: https://bugzilla.mozilla.org/show_bug.cgi?id=1714064

But now it seems to be rather Rust issue.

Unfortunately I wasn't able to reproduce it outside of Firefox yet:

C++ code calls wr_dp_push_stacking_context() with parameter aParams.mFilterDatas.Length() which is zero (0):

https://searchfox.org/mozilla-central/rev/79d73b4aff88dd4a0f06dd3789e1148c49b0de60/gfx/webrender_bindings/WebRenderAPI.cpp#1028

But Rust code gets instead of 0 some nonsense number (e.g. 133081200598864):

https://searchfox.org/mozilla-central/rev/79d73b4aff88dd4a0f06dd3789e1148c49b0de60/gfx/webrender_bindings/src/bindings.rs#2455

I was able to limit the wr_dp_push_stacking_context() to just:

#[no_mangle]
pub extern "C" fn wr_dp_push_stacking_context(
    bounds: LayoutRect,
    filter_count: usize,
    glyph_raster_space: RasterSpace,
    params: &WrStackingContextParams,
)  {
    debug_assert!(unsafe { !is_in_render_thread() });
    println!("XXX start {}", filter_count);
}

And the problem is still there. But when I swap bounds: LayoutRect with filter_count: usize then filter_count is passed correctly!

LayoutRect is quite complicated (to me):
https://searchfox.org/mozilla-central/rev/79d73b4aff88dd4a0f06dd3789e1148c49b0de60/gfx/wr/webrender_api/src/units.rs#86
Important might be that it uses floating numbers!

Following is disassembled wr_dp_push_stacking_context function as defined above:

wr_dp_push_stacking_context:    save      %sp, -0x160, %sp
wr_dp_push_stacking_context+4:  call      +0x8          <wr_dp_push_stacking_context+0xc>
wr_dp_push_stacking_context+8:  sethi     %hi(0x3b05800), %i0
wr_dp_push_stacking_context+0xc:or        %i0, 0x3f8, %i0
wr_dp_push_stacking_context+0x10:       add       %i0, %o7, %i0
wr_dp_push_stacking_context+0x14:       stx       %i0, [%fp + 0x767]
wr_dp_push_stacking_context+0x18:       ldx       [%fp + 0x8af], %i0
wr_dp_push_stacking_context+0x1c:       st        %f1, [%fp + 0x787]
wr_dp_push_stacking_context+0x20:       st        %f3, [%fp + 0x78b]
wr_dp_push_stacking_context+0x24:       st        %f5, [%fp + 0x78f]
wr_dp_push_stacking_context+0x28:       st        %f7, [%fp + 0x793]
wr_dp_push_stacking_context+0x2c:       ld        [%fp + 0x787], %i0
wr_dp_push_stacking_context+0x30:       sllx      %i0, 0x20, %i0
wr_dp_push_stacking_context+0x34:       ld        [%fp + 0x78b], %i1
wr_dp_push_stacking_context+0x38:       or        %i0, %i1, %i0
wr_dp_push_stacking_context+0x3c:       stx       %i0, [%fp + 0x777]
wr_dp_push_stacking_context+0x40:       ld        [%fp + 0x78f], %i0
wr_dp_push_stacking_context+0x44:       sllx      %i0, 0x20, %i0
wr_dp_push_stacking_context+0x48:       ld        [%fp + 0x793], %i1
wr_dp_push_stacking_context+0x4c:       or        %i0, %i1, %i0
wr_dp_push_stacking_context+0x50:       stx       %i0, [%fp + 0x77f]
wr_dp_push_stacking_context+0x54:       stx       %i4, [%fp + 0x797]
wr_dp_push_stacking_context+0x58:       stx       %i5, [%fp + 0x7a7]
wr_dp_push_stacking_context+0x5c:       call      -0xae63cb0    <is_in_render_thread>
wr_dp_push_stacking_context+0x60:       stx       %i5, [%fp + 0x79f]
wr_dp_push_stacking_context+0x64:       ba        +0x8          <wr_dp_push_stacking_context+0x6c>
wr_dp_push_stacking_context+0x68:       st        %o0, [%fp + 0x773]
wr_dp_push_stacking_context+0x6c:       ld        [%fp + 0x773], %i0
wr_dp_push_stacking_context+0x70:       cmp       %i0, 0x0
wr_dp_push_stacking_context+0x74:       be        +0x38         <wr_dp_push_stacking_context+0xac>
wr_dp_push_stacking_context+0x78:       nop
wr_dp_push_stacking_context+0x7c:       ba        +0x8          <wr_dp_push_stacking_context+0x84>
wr_dp_push_stacking_context+0x80:       nop
wr_dp_push_stacking_context+0x84:       ldx       [%fp + 0x767], %i0
wr_dp_push_stacking_context+0x88:       sethi     %hi(0x35c00), %i1
wr_dp_push_stacking_context+0x8c:       add       %i1, 0x3b8, %i1
wr_dp_push_stacking_context+0x90:       ldx       [%i0 + %i1], %o0
wr_dp_push_stacking_context+0x94:       sethi     %hi(0x36000), %i1
wr_dp_push_stacking_context+0x98:       add       %i1, 0x50, %i1
wr_dp_push_stacking_context+0x9c:       ldx       [%i0 + %i1], %o2
wr_dp_push_stacking_context+0xa0:       call      +0x3c7726c    <PLT:_ZN4core9panicking5panic17he6543f3ddbf0355fE>
wr_dp_push_stacking_context+0xa4:       mov       0x33, %o1
wr_dp_push_stacking_context+0xa8:       ta        %icc, 0x5
wr_dp_push_stacking_context+0xac:       ldx       [%fp + 0x767], %i0
wr_dp_push_stacking_context+0xb0:       add       %fp, 0x797, %o0
wr_dp_push_stacking_context+0xb4:       stx       %o0, [%fp + 0x7ef]
wr_dp_push_stacking_context+0xb8:       stx       %o0, [%fp + 0x7f7]
wr_dp_push_stacking_context+0xbc:       sethi     %hi(0x1400), %i1
wr_dp_push_stacking_context+0xc0:       add       %i1, 0x190, %i1
wr_dp_push_stacking_context+0xc4:       call      +0x3c81028    <PLT:_ZN4core3fmt10ArgumentV13new17ha9bc9565de3aadf7E>
wr_dp_push_stacking_context+0xc8:       ldx       [%i0 + %i1], %o1
wr_dp_push_stacking_context+0xcc:       stx       %o0, [%fp + 0x757]
wr_dp_push_stacking_context+0xd0:       ba        +0x8          <wr_dp_push_stacking_context+0xd8>
wr_dp_push_stacking_context+0xd4:       stx       %o1, [%fp + 0x75f]
wr_dp_push_stacking_context+0xd8:       ldx       [%fp + 0x767], %i0
wr_dp_push_stacking_context+0xdc:       ldx       [%fp + 0x75f], %i1
wr_dp_push_stacking_context+0xe0:       ldx       [%fp + 0x757], %i2
wr_dp_push_stacking_context+0xe4:       stx       %i2, [%fp + 0x7df]
wr_dp_push_stacking_context+0xe8:       stx       %i1, [%fp + 0x7e7]
wr_dp_push_stacking_context+0xec:       sethi     %hi(0x36000), %i1
wr_dp_push_stacking_context+0xf0:       add       %i1, 0x58, %i1
wr_dp_push_stacking_context+0xf4:       ldx       [%i0 + %i1], %o1
wr_dp_push_stacking_context+0xf8:       add       %fp, 0x7af, %o0
wr_dp_push_stacking_context+0xfc:       mov       0x2, %o2
wr_dp_push_stacking_context+0x100:      add       %fp, 0x7df, %o3
wr_dp_push_stacking_context+0x104:      call      +0xe2a0c      <core::fmt::Arguments::new_v1::h337fca81b2e584b1>
wr_dp_push_stacking_context+0x108:      mov       0x1, %o4
wr_dp_push_stacking_context+0x10c:      ba        +0x8          <wr_dp_push_stacking_context+0x114>
wr_dp_push_stacking_context+0x110:      nop
wr_dp_push_stacking_context+0x114:      call      +0x3df5ab0    <PLT:_ZN3std2io5stdio6_print17h02792fbd1097b851E>
wr_dp_push_stacking_context+0x118:      add       %fp, 0x7af, %o0
wr_dp_push_stacking_context+0x11c:      ba        +0x8          <wr_dp_push_stacking_context+0x124>
wr_dp_push_stacking_context+0x120:      nop
wr_dp_push_stacking_context+0x124:      ret
wr_dp_push_stacking_context+0x128:      restore

[nagisa]

Sounds like an ABI definition issue (e.g. something is passed via a value while it should be passed via a pointer). Marking this as unsound, as instead of a pointer, this could be mangling a pointer or a reference. Can we see the disassembly for the calling side as well?

Could you also try to produce a MCVE (a test case that does not rely on external crates?) by inlining the type definitions, etc. Also helpful would be a removal of the panics, e.g. by replacing them with if filter_count != 0 { std::intrinsics::abort() }. Or something along those lines.

[psumbera]

Following is DisplayListBuilder::PushStackingContext() which I use now for debugging:

Maybe<wr::WrSpatialId> DisplayListBuilder::PushStackingContext(
    const wr::StackingContextParams& aParams, const wr::LayoutRect& aBounds,
    const wr::RasterSpace& aRasterSpace) {
  MOZ_ASSERT(mClipChainLeaf.isNothing(),
             "Non-empty leaf from clip chain given, but not used with SC!");

  wr::LayoutTransform matrix;
  const gfx::Matrix4x4* transform = aParams.mTransformPtr;
  if (transform) {
    matrix = ToLayoutTransform(*transform);
  }
  const wr::LayoutTransform* maybeTransform = transform ? &matrix : nullptr;
  WRDL_LOG("PushStackingContext b=%s t=%s\n", mWrState,
           ToString(aBounds).c_str(),
           transform ? ToString(*transform).c_str() : "none");
  printf("XXX before %ld %ld\n", aParams.mFilters.Length(), aParams.mFilterDatas.Length());
  wr_dp_push_stacking_context(
      aBounds,
      123456789,
      aRasterSpace,
      &aParams);
  return Nothing();
}

And this is its disassembly (_ZN7mozilla2wr18DisplayListBuilder19PushStackingContextERKNS0_21StackingContextParamsERKNS0_4RectIfNS0_11LayoutPixelEEERKNS0_11RasterSpaceE):

0:           save      %sp, -0x180, %sp
+4:          sethi     %hi(0xe374c00), %l7
+8:          add       %l7, 0x3bc, %l7
+0xc:        call      -0x2b0f6dc    <0x10c78ee8>
+0x10:       nop
+0x14:       mov       %l7, %i5
+0x18:       stx       %i0, [%fp + 0x797]
+0x1c:       stx       %i1, [%fp + 0x78f]
+0x20:       stx       %i2, [%fp + 0x787]
+0x24:       stx       %i3, [%fp + 0x77f]
+0x28:       stx       %i4, [%fp + 0x777]
+0x2c:       sethi     %hi(0x0), %g1
+0x30:       xor       %g1, 0x40, %g1
+0x34:       ldx       [%i5 + %g1], %g1
+0x38:       ldx       [%g1], %g2
+0x3c:       stx       %g2, [%fp + 0x7f7]
+0x40:       clr       %g2
+0x44:       ldx       [%fp + 0x78f], %g1
+0x48:       add       %g1, 0x50, %g1
+0x4c:       mov       %g1, %o0
+0x50:       call      +0xe02c       <_ZNK7mozilla5MaybeINS_2wr4RectIfNS1_11LayoutPixelEEEE9isNothingEv>
+0x54:       nop
+0x58:       mov       %o0, %g1
+0x5c:       xor       %g1, 0x1, %g1
+0x60:       and       %g1, 0xff, %g1
+0x64:       mov       %g1, %g2
+0x68:       clr       %g1
+0x6c:       movrne    %g2, 0x1, %g1
+0x70:       and       %g1, 0xff, %g1
+0x74:       cmp       %g1, 0x0
+0x78:       be,pt     %icc, +0x60   <_ZN7mozilla2wr18DisplayListBuilder19PushStackingContextERKNS0_21StackingContextParamsERKNS0_4RectIfNS0_11LayoutPixelEEERKNS0_11RasterSpaceE+0xd8>
+0x7c:       nop
+0x80:       mov       0x3f7, %o2
+0x84:       sethi     %hi(0x128ecc00), %g1
+0x88:       xor       %g1, -0x398, %g1
+0x8c:       add       %i5, %g1, %g1
+0x90:       mov       %g1, %o1
+0x94:       sethi     %hi(0x128ecc00), %g1
+0x98:       xor       %g1, -0xc0, %g1
+0x9c:       add       %i5, %g1, %g1
+0xa0:       mov       %g1, %o0
+0xa4:       call      -0x5408       <MOZ_ReportAssertionFailure>
+0xa8:       nop
+0xac:       sethi     %hi(0x128ecc00), %g1
+0xb0:       xor       %g1, -0x60, %g1
+0xb4:       add       %i5, %g1, %g1
+0xb8:       mov       %g1, %o0
+0xbc:       call      -0x545c       <_ZL22AnnotateMozCrashReasonPKc>
+0xc0:       nop
+0xc4:       clr       %g2
+0xc8:       mov       0x3f7, %g1 _ZN7mozilla2wr18DisplayListBuilder19PushStackingContextERKNS0_21StackingContextParamsERKNS0_4RectIfNS0_11LayoutPixelEEERKNS0_11RasterSpaceE+0xcc:       st        %g1, [%g2]
+0xd0:       call      +0xe440198    <PLT:abort>
+0xd4:       nop
+0xd8:       ldx       [%fp + 0x787], %g1
+0xdc:       ldx       [%g1 + 0x68], %g1
+0xe0:       stx       %g1, [%fp + 0x7a7]
+0xe4:       ldx       [%fp + 0x7a7], %g1
+0xe8:       brz,pt    %g1, +0x3c    <_ZN7mozilla2wr18DisplayListBuilder19PushStackingContextERKNS0_21StackingContextParamsERKNS0_4RectIfNS0_11LayoutPixelEEERKNS0_11RasterSpaceE+0x124>
+0xec:       nop
+0xf0:       add       %fp, 0x72f, %g1
+0xf4:       ldx       [%fp + 0x7a7], %o1
+0xf8:       mov       %g1, %o0
+0xfc:       call      +0x5608       <_ZN7mozilla2wrL17ToLayoutTransformINS_3gfx12UnknownUnitsES3_EENS0_11Transform3DIfNS0_11LayoutPixelES5_EERKNS2_14Matrix4x4TypedIT_T0_fEE>
+0x100:      nop
+0x104:      add       %fp, 0x7b7, %g1
+0x108:      add       %fp, 0x72f, %g2
+0x10c:      mov       0x40, %g3
+0x110:      mov       %g3, %o2
+0x114:      mov       %g2, %o1
+0x118:      mov       %g1, %o0
+0x11c:      call      +0xe440d0c    <PLT:memcpy>
+0x120:      nop
+0x124:      ldx       [%fp + 0x7a7], %g1
+0x128:      brz,pt    %g1, +0x14    <_ZN7mozilla2wr18DisplayListBuilder19PushStackingContextERKNS0_21StackingContextParamsERKNS0_4RectIfNS0_11LayoutPixelEEERKNS0_11RasterSpaceE+0x13c>
+0x12c:      nop
+0x130:      add       %fp, 0x7b7, %g1
+0x134:      ba,pt     %xcc, +0xc    <_ZN7mozilla2wr18DisplayListBuilder19PushStackingContextERKNS0_21StackingContextParamsERKNS0_4RectIfNS0_11LayoutPixelEEERKNS0_11RasterSpaceE+0x140>
+0x138:      nop
+0x13c:      clr       %g1
+0x140:      stx       %g1, [%fp + 0x7af]
+0x144:      ldx       [%fp + 0x787], %g1
+0x148:      add       %g1, 0x40, %g1
+0x14c:      mov       %g1, %o0
+0x150:      call      -0x2ac7a84    <_ZNK13nsTArray_baseI27nsTArrayInfallibleAllocator30nsTArray_RelocateUsingMemutilsE6LengthEv>
+0x154:      nop
+0x158:      mov       %o0, %i4
+0x15c:      ldx       [%fp + 0x787], %g1
+0x160:      add       %g1, 0x48, %g1
+0x164:      mov       %g1, %o0
+0x168:      call      -0x2ac7a9c    <_ZNK13nsTArray_baseI27nsTArrayInfallibleAllocator30nsTArray_RelocateUsingMemutilsE6LengthEv>
+0x16c:      nop
+0x170:      mov       %o0, %g1
+0x174:      mov       %g1, %o2
+0x178:      mov       %i4, %o1
+0x17c:      sethi     %hi(0x128ec800), %g1
+0x180:      xor       %g1, -0x3f8, %g1
+0x184:      add       %i5, %g1, %g1
+0x188:      mov       %g1, %o0
+0x18c:      call      +0xe445dfc    <PLT:printf>
+0x190:      nop
+0x194:      ldx       [%fp + 0x787], %g3
+0x198:      ldx       [%fp + 0x777], %g1
+0x19c:      ld        [%g1], %g2
+0x1a0:      srl       %g2, 0x0, %g2
+0x1a4:      sllx      %g2, 0x20, %g2
+0x1a8:      ld        [%g1 + 0x4], %g1
+0x1ac:      srl       %g1, 0x0, %g1
+0x1b0:      or        %g1, %g2, %g2
+0x1b4:      ldx       [%fp + 0x77f], %g1
+0x1b8:      ld        [%g1], %f11
+0x1bc:      ld        [%g1 + 0x4], %f10
+0x1c0:      ld        [%g1 + 0x8], %f9
+0x1c4:      ld        [%g1 + 0xc], %f8
+0x1c8:      mov       %g3, %o4
+0x1cc:      mov       %g2, %o3
+0x1d0:      sethi     %hi(0x75bcc00), %g1
+0x1d4:      or        %g1, 0x115, %o2
+0x1d8:      fmovs     %f11, %f0
+0x1dc:      fmovs     %f10, %f1
+0x1e0:      fmovs     %f9, %f2
+0x1e4:      fmovs     %f8, %f3
+0x1e8:      call      +0xa86f234    <wr_dp_push_stacking_context>
+0x1ec:      nop
+0x1f0:      mov       %l0, %g1
+0x1f4:      and       %g1, 0xff, %g1
+0x1f8:      sllx      %g1, 0x38, %g1
+0x1fc:      mov       %g1, %o1
+0x200:      ldx       [%fp + 0x797], %o0
+0x204:      call      +0xdec4       <_ZN7mozilla5MaybeINS_2wr11WrSpatialIdEEC1ENS_7NothingE>
+0x208:      nop
+0x20c:      sethi     %hi(0x0), %g1
+0x210:      xor       %g1, 0x40, %g1
+0x214:      ldx       [%i5 + %g1], %g1
+0x218:      ldx       [%fp + 0x7f7], %g2
+0x21c:      ldx       [%g1], %g1
+0x220:      xor       %g2, %g1, %g2
+0x224:      clr       %g1
+0x228:      mov       %g2, %g1
+0x22c:      brz,pt    %g1, +0x10    <_ZN7mozilla2wr18DisplayListBuilder19PushStackingContextERKNS0_21StackingContextParamsERKNS0_4RectIfNS0_11LayoutPixelEEERKNS0_11RasterSpaceE+0x23c>
+0x230:      nop
+0x234:      call      +0xe440074    <PLT:__stack_chk_fail>
+0x238:      nop
+0x23c:      ldx       [%fp + 0x797], %i0
+0x240:      return    %i7 + 0x8
+0x244:      nop

And here is again my wr_dp_push_stacking_context() now without debug_assert:

#[no_mangle]
pub extern "C" fn wr_dp_push_stacking_context(
    bounds: LayoutRect,
    filter_count: usize,
    glyph_raster_space: RasterSpace,
    params: &WrStackingContextParams,
)  {
    println!("XXX start {}", filter_count);
}

And it's disassembly is:

wr_dp_push_stacking_context:    save      %sp, -0x150, %sp
wr_dp_push_stacking_context+4:  call      +0x8          <wr_dp_push_stacking_context+0xc>
wr_dp_push_stacking_context+8:  sethi     %hi(0x3b05800), %i0
wr_dp_push_stacking_context+0xc:or        %i0, 0x3a8, %i0
wr_dp_push_stacking_context+0x10:       add       %i0, %o7, %i0
wr_dp_push_stacking_context+0x14:       stx       %i0, [%fp + 0x75f]
wr_dp_push_stacking_context+0x18:       ldx       [%fp + 0x8af], %i1
wr_dp_push_stacking_context+0x1c:       st        %f1, [%fp + 0x787]
wr_dp_push_stacking_context+0x20:       st        %f3, [%fp + 0x78b]
wr_dp_push_stacking_context+0x24:       st        %f5, [%fp + 0x78f]
wr_dp_push_stacking_context+0x28:       st        %f7, [%fp + 0x793]
wr_dp_push_stacking_context+0x2c:       ld        [%fp + 0x787], %i1
wr_dp_push_stacking_context+0x30:       sllx      %i1, 0x20, %i1
wr_dp_push_stacking_context+0x34:       ld        [%fp + 0x78b], %i2
wr_dp_push_stacking_context+0x38:       or        %i1, %i2, %i1
wr_dp_push_stacking_context+0x3c:       stx       %i1, [%fp + 0x777]
wr_dp_push_stacking_context+0x40:       ld        [%fp + 0x78f], %i1
wr_dp_push_stacking_context+0x44:       sllx      %i1, 0x20, %i1
wr_dp_push_stacking_context+0x48:       ld        [%fp + 0x793], %i2
wr_dp_push_stacking_context+0x4c:       or        %i1, %i2, %i1
wr_dp_push_stacking_context+0x50:       stx       %i1, [%fp + 0x77f]
wr_dp_push_stacking_context+0x54:       stx       %i4, [%fp + 0x797]
wr_dp_push_stacking_context+0x58:       stx       %i5, [%fp + 0x7a7]
wr_dp_push_stacking_context+0x5c:       stx       %i5, [%fp + 0x79f]
wr_dp_push_stacking_context+0x60:       add       %fp, 0x797, %o0
wr_dp_push_stacking_context+0x64:       stx       %o0, [%fp + 0x7ef]
wr_dp_push_stacking_context+0x68:       stx       %o0, [%fp + 0x7f7]
wr_dp_push_stacking_context+0x6c:       sethi     %hi(0x1400), %i1
wr_dp_push_stacking_context+0x70:       add       %i1, 0x190, %i1
wr_dp_push_stacking_context+0x74:       call      +0x3c81078    <PLT:_ZN4core3fmt10ArgumentV13new17ha9bc9565de3aadf7E>
wr_dp_push_stacking_context+0x78:       ldx       [%i0 + %i1], %o1
wr_dp_push_stacking_context+0x7c:       stx       %o0, [%fp + 0x767]
wr_dp_push_stacking_context+0x80:       ba        +0x8          <wr_dp_push_stacking_context+0x88>
wr_dp_push_stacking_context+0x84:       stx       %o1, [%fp + 0x76f]
wr_dp_push_stacking_context+0x88:       ldx       [%fp + 0x75f], %i0
wr_dp_push_stacking_context+0x8c:       ldx       [%fp + 0x76f], %i1
wr_dp_push_stacking_context+0x90:       ldx       [%fp + 0x767], %i2
wr_dp_push_stacking_context+0x94:       stx       %i2, [%fp + 0x7df]
wr_dp_push_stacking_context+0x98:       stx       %i1, [%fp + 0x7e7]
wr_dp_push_stacking_context+0x9c:       sethi     %hi(0x36000), %i1
wr_dp_push_stacking_context+0xa0:       add       %i1, 0x50, %i1
wr_dp_push_stacking_context+0xa4:       ldx       [%i0 + %i1], %o1
wr_dp_push_stacking_context+0xa8:       add       %fp, 0x7af, %o0
wr_dp_push_stacking_context+0xac:       mov       0x2, %o2
wr_dp_push_stacking_context+0xb0:       add       %fp, 0x7df, %o3
wr_dp_push_stacking_context+0xb4:       call      +0xe2a0c      <_ZN4core3fmt9Arguments6new_v117h337fca81b2e584b1E>
wr_dp_push_stacking_context+0xb8:       mov       0x1, %o4
wr_dp_push_stacking_context+0xbc:       ba        +0x8          <wr_dp_push_stacking_context+0xc4>
wr_dp_push_stacking_context+0xc0:       nop
wr_dp_push_stacking_context+0xc4:       call      +0x3df5b00    <PLT:_ZN3std2io5stdio6_print17h02792fbd1097b851E>
wr_dp_push_stacking_context+0xc8:       add       %fp, 0x7af, %o0
wr_dp_push_stacking_context+0xcc:       ba        +0x8          <wr_dp_push_stacking_context+0xd4>
wr_dp_push_stacking_context+0xd0:       nop
wr_dp_push_stacking_context+0xd4:       ret
wr_dp_push_stacking_context+0xd8:       restore

[batrla]

Agreed looks like Rust's SPARCv9 64-bit ABI definition issue. In more detail, it seems to me Rust thinks the floating point registers are 64-bit, while they are still 32-bit in the processor [1]. The mismatch causes Rust function to read garbage when the argument is structure containing floats and it is passed by value.

Here's a small test case, where C calls into Rust:

$ cat franta.rs 
#[derive(Debug)]
#[no_mangle]
#[repr(C)]
pub struct Franta {
        a:f32,
        b:f32,
        c:f32,
        d:f32,
}

#[no_mangle]
pub extern "C" fn funkce(arg: Franta, i: i32)
{
    println!("XXX start {:?} {}", arg, i);
}

$ cat testfranta.c 
#include <stdio.h>
struct Franta {
        float a;
        float b;
        float c;
        float d;
};

void
funkce(struct Franta a, int b);

int main() {
        struct Franta a = { 1, 2.0, 2.1, 2.2};
        funkce(a, 3);
        return 0;
}

rustc  --crate-type dylib franta.rs 
gcc ./testfranta.c ./libfranta.so 

$ file a.out 
a.out:          ELF 64-bit MSB executable SPARCV9 Version 1, UltraSPARC3
Extensions Required, dynamically linked, not stripped

$ ./a.out 
XXX start Franta { a: 2.0, b: 2.2, c: NaN, d: NaN } 2136736064

Expected output:
XXX start Franta { a: 1, b: 2.0, c: 2.1, d: 2.2 } 3

Actual output:
XXX start Franta { a: 2.0, b: 2.2, c: NaN, d: NaN } 2136736064

The disassembler shows:

main+0x74:                      mov       0x3, %o2
main+0x78:                      fmovs     %f11, %f0
main+0x7c:                      fmovs     %f10, %f1
main+0x80:                      fmovs     %f9, %f2
main+0x84:                      fmovs     %f8, %f3
main+0x88:                      call      +0x100278     <PLT=libfranta.so`funkce>
main+0x8c:                      nop

That the caller passes arguments via %f0, %f1, %f2, %f3, %o2,
But callee reads arguments from:

funkce+0x14:                    fmovs     %f7, %f0
funkce+0x18:                    fmovs     %f5, %f2
funkce+0x1c:                    fmovs     %f3, %f4
funkce+0x20:                    fmovs     %f1, %f6
funkce+0x24:                    mov       %i4, %i1

^ caller reads arguments from %f1, %f3, %f5, %f7 that are lower 32-bit parts of double precision (64-bit) floating point registers. So while Rust correctly interprets the structure members as f32, it seems it thinks they are passed in the aggregate (structure) as f64!? At the end Rust reads the second argument of function funkce from %i4 (skips 4x64-bits -> %i0, %i1, %i2, %i3), however, the caller has put it in %i2 (skipping 4x32 bits -> %i0, %i1 since all %i registers are 64-bit wide). The difference in how many input arguments are skipped by Rust and Gcc is another evidence that there's mismatch in size of floating point members of structure passed by value as first argument.

Is the function is_homogenous_aggregate() in librustc_trans/cabi_sparc64.rs right place to look at to check if it correctly sets argument size?

[1] section 5.1.4 in SPARC Architecture Manual,
https://sparc.org/wp-content/uploads/2014/01/SPARCV9.pdf.gz

[nagisa]

That function, or rather the file in its entirety is a correct place to look at, yes. Looking at the LLVM IR, this is the signature generated by Rust today:

@funkce([4 x float] %0, i32 signext %i) unnamed_addr

Whereas it really ought to be

@funkce(float, float, float, float, i32) unnamed_addr

or similar. It does seem that is_homogenous_aggregate is involved in at least some way, here.

[psumbera]

I guess that the same problem is also on SPARC Linux. @glaubitz can you please test above test case?

[glaubitz]

On Linux, I'm getting:

glaubitz@gcc202:~$ rustc --crate-type dylib franta.rs
warning: attribute should be applied to a function or static
 --> franta.rs:2:1
  |
2 |   #[no_mangle]
  |   ^^^^^^^^^^^^
3 |   #[repr(C)]
4 | / pub struct Franta {
5 | |         a:f32,
6 | |         b:f32,
7 | |         c:f32,
8 | |         d:f32,
9 | | }
  | |_- not a function or static
  |
  = note: `#[warn(unused_attributes)]` on by default
  = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!

warning: 1 warning emitted

glaubitz@gcc202:~$ gcc ./testfranta.c ./libfranta.so 
glaubitz@gcc202:~$ ./a.out 
./a.out: error while loading shared libraries: libfranta.so: cannot open shared object file: No such file or directory
glaubitz@gcc202:~$ LD_LIBRARY_PATH=. ./a.out 
XXX start Franta { a: 2.0, b: 2.2, c: 0.0, d: 0.0 } 0
glaubitz@gcc202:~$