1702487 - jitsrc could be useful for tracing bytecode generation, but needs more patterns

Status: RESOLVED FIXED

(Core :: JavaScript Engine, enhancement, P5)

Description

[Matthew Gaudet (he/him) [:mgaudet]]

The jitsrc.py gdb script could be perfect for finding the original emission point of bytecode, but it does need additional patterns to support this.

In the interpreter I ran

(rr) print script->code() // Turns out this suffices, as I'm interested in where the first op came from! 
$53 = 0x7f89bdee9d61 (JSOp::Uninitialized)
(rr) jitsrc 0x7f89bdee9d61
Thread 1 hit Hardware watchpoint -580: *0x7f89bdee9d61
Old value = 43946
New value = -469718102
0x000055e490a71132 in std::__copy_move<false, false, std::random_access_iterator_tag>::__copy_m<mozilla::span_details::span_iterator<mozilla::Span<unsigned char const, 18446744073709551615ul>, true>, mozilla::span_details::span_iterator<mozilla::Span<unsigned char, 18446744073709551615ul>, false> > (__first=..., __last=..., __result=...) at /usr/lib/gcc/x86_64-linux-gnu/7.5.0/../../../../include/c++/7.5.0/bits/stl_algobase.h:324
324                   *__result = *__first;
(rr) bt
#0  0x000055e490a71132 in std::__copy_move<false, false, std::random_access_iterator_tag>::__copy_m<mozilla::span_details::span_iterator<mozilla::Span<unsigned char const, 18446744073709551615ul>, true>, mozilla::span_details::span_iterator<mozilla::Span<unsigned char, 18446744073709551615ul>, false> >(mozilla::span_details::span_iterator<mozilla::Span<unsigned char const, 18446744073709551615ul>, true>, mozilla::span_details::span_iterator<mozilla::Span<unsigned char const, 18446744073709551615ul>, true>, mozilla::span_details::span_iterator<mozilla::Span<unsigned char, 18446744073709551615ul>, false>) (__first=..., __last=..., __result=...) at /usr/lib/gcc/x86_64-linux-gnu/7.5.0/../../../../include/c++/7.5.0/bits/stl_algobase.h:324
#1  0x000055e490a70ff1 in std::__copy_move_a<false, mozilla::span_details::span_iterator<mozilla::Span<unsigned char const, 18446744073709551615ul>, true>, mozilla::span_details::span_iterator<mozilla::Span<unsigned char, 18446744073709551615ul>, false> >(mozilla::span_details::span_iterator<mozilla::Span<unsigned char const, 18446744073709551615ul>, true>, mozilla::span_details::span_iterator<mozilla::Span<unsigned char const, 18446744073709551615ul>, true>, mozilla::span_details::span_iterator<mozilla::Span<unsigned char, 18446744073709551615ul>, false>) (__first=..., __last=..., __result=...) at /usr/lib/gcc/x86_64-linux-gnu/7.5.0/../../../../include/c++/7.5.0/bits/stl_algobase.h:385
#2  0x000055e490a70eaa in std::__copy_move_a2<false, mozilla::span_details::span_iterator<mozilla::Span<unsigned char const, 18446744073709551615ul>, true>, mozilla::span_details::span_iterator<mozilla::Span<unsigned char, 18446744073709551615ul>, false> >(mozilla::span_details::span_iterator<mozilla::Span<unsigned char const, 18446744073709551615ul>, true>, mozilla::span_details::span_iterator<mozilla::Span<unsigned char const, 18446744073709551615ul>, true>, mozilla::span_details::span_iterator<mozilla::Span<unsigned char, 18446744073709551615ul>, false>) (__first=..., __last=..., __result=...) at /usr/lib/gcc/x86_64-linux-gnu/7.5.0/../../../../include/c++/7.5.0/bits/stl_algobase.h:422
#3  0x000055e490a70c64 in std::copy<mozilla::span_details::span_iterator<mozilla::Span<unsigned char const, 18446744073709551615ul>, true>, mozilla::span_details::span_iterator<mozilla::Span<unsigned char, 18446744073709551615ul>, false> >(mozilla::span_details::span_iterator<mozilla::Span<unsigned char const, 18446744073709551615ul>, true>, mozilla::span_details::span_iterator<mozilla::Span<unsigned char const, 18446744073709551615ul>, true>, mozilla::span_details::span_iterator<mozilla::Span<unsigned char, 18446744073709551615ul>, false>) (__first=..., __last=..., __result=...) at /usr/lib/gcc/x86_64-linux-gnu/7.5.0/../../../../include/c++/7.5.0/bits/stl_algobase.h:454
#4  0x000055e490a1ee62 in CopySpan<mozilla::Span<unsigned char const, 18446744073709551615ul>, mozilla::Span<unsigned char, 18446744073709551615ul> >(mozilla::Span<unsigned char const, 18446744073709551615ul> const&, mozilla::Span<unsigned char, 18446744073709551615ul>) (source=..., target=...) at /home/matthew/unified/js/src/vm/JSScript.cpp:4520
#5  0x000055e4909e4318 in js::ImmutableScriptData::new_(JSContext*, unsigned int, unsigned int, unsigned int, js::GCThingIndex, unsigned int, bool, unsigned short, mozilla::Span<unsigned char const, 18446744073709551615ul>, mozilla::Span<js::SrcNote const, 18446744073709551615ul>, mozilla::Span<unsigned int const, 18446744073709551615ul>, mozilla::Span<js::ScopeNote const, 18446744073709551615ul>, mozilla::Span<js::TryNote const, 18446744073709551615ul>) (cx=0x7f89bde50000, mainOffset=0, nfixed=1, nslots=9, bodyScopeIndex=..., numICEntries=26, isFunction=false, funLength=0, code=..., notes=..., resumeOffsets=..., scopeNotes=..., tryNotes=...) at /home/matthew/unified/js/src/vm/JSScript.cpp:4563
#6  0x000055e49104389c in js::frontend::BytecodeEmitter::createImmutableScriptData(JSContext*) (this=0x7ffc2e731558, cx=0x7f89bde50000) at /home/matthew/unified/js/src/frontend/BytecodeEmitter.cpp:2694
#7  0x000055e491043165 in js::frontend::BytecodeEmitter::intoScriptStencil(js::frontend::TypedIndex<js::frontend::ScriptStencil>) (this=0x7ffc2e731558, scriptIndex=...) at /home/matthew/unified/js/src/frontend/BytecodeEmitter.cpp:11666

So we get lost inside Span copying

Comment 1

[Iain Ireland [:iain]]

Attachment: Bug 1702487: Support bytecode generation in jitsrc r=mgaudet

Here's my fifteen minute attempt at support. Test it out and let me know if anything breaks / is missing.

EndianUtils::copyAndSwapTo is used for self-hosted code. The 0,0 checks for Little->Little, which is just a memcpy.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/947bf0db49d3
Support bytecode generation in jitsrc r=mgaudet

Comment 3

[Atila Butkovits]

https://hg.mozilla.org/mozilla-central/rev/947bf0db49d3