Correctly compute field path for the heap snapshot, taking struct inlining into account by NHDaly · Pull Request #1 · vilterp/julia

NHDaly · 2021-10-14T16:43:17Z

The existing debug code for computing field name from a slot pointer is not working: gc_slot_to_fieldidx(parent, slot).

I think this is because that code was written before the optimization that was added in julia 1.3 or 1.4 to allow inlining immutable structs with heap references.

This PR creates a new function, _fieldpath_for_slot(from, slot) which returns a vector of type, field pairs, that give the full path to a slot's field from a given object.

For example, for the following struct:

struct B
    x::Int
    y::Any
end
mutable struct A
    a::Int
    b::B
end

ga = A(1, B(2, []))

The only pointer field in ga is: b.y :: Vector{Any}, which is returned as [(B, :y), (A, :b)] (in reverse order because of silly implementation reasons, since C++ vectors aren't efficient for push_front).

Account for inline-allocated structs in field path. Only partway done.

maybe still need to do the off-by-one jameson mentioned? 🤔

It works now!! ``` - ga::Main.A @302073680 - b.y::Array{Any, 1} @302026704 ```

NHDaly

@vilterp i think this LGTM. Do you want to have a look at it?

vilterp · 2021-10-14T16:53:16Z

src/gc-heap-snapshot.cpp

+    // Build the new field name by joining the strings, and/or use the struct + field names
+    // to create a bunch of edges + nodes
+    // (iterate the vector in reverse - the last element is the first path)
+    // TODO: Prefer to create intermediate edges and nodes instead of a combined string path.


I honestly don't mind the combined path 🤔 🤷‍♂️

yeah, i'm not sure what to think about it either. After we talked, I tried adding the (b::B).y type syntax, but it's a bit difficult / awkward, so i didn't 😅. String processing in C++ is TOO HARD

…Lang#45790) Currently the `@nospecialize`-d `push!(::Vector{Any}, ...)` can only take a single item and we will end up with runtime dispatch when we try to call it with multiple items: ```julia julia> code_typed(push!, (Vector{Any}, Any)) 1-element Vector{Any}: CodeInfo( 1 ─ $(Expr(:foreigncall, :(:jl_array_grow_end), Nothing, svec(Any, UInt64), 0, :(:ccall), Core.Argument(2), 0x0000000000000001, 0x0000000000000001))::Nothing │ %2 = Base.arraylen(a)::Int64 │ Base.arrayset(true, a, item, %2)::Vector{Any} └── return a ) => Vector{Any} julia> code_typed(push!, (Vector{Any}, Any, Any)) 1-element Vector{Any}: CodeInfo( 1 ─ %1 = Base.append!(a, iter)::Vector{Any} └── return %1 ) => Vector{Any} ``` This commit adds a new specialization that it can take arbitrary-length items. Our compiler should still be able to optimize the single-input case as before via the dispatch mechanism. ```julia julia> code_typed(push!, (Vector{Any}, Any)) 1-element Vector{Any}: CodeInfo( 1 ─ $(Expr(:foreigncall, :(:jl_array_grow_end), Nothing, svec(Any, UInt64), 0, :(:ccall), Core.Argument(2), 0x0000000000000001, 0x0000000000000001))::Nothing │ %2 = Base.arraylen(a)::Int64 │ Base.arrayset(true, a, item, %2)::Vector{Any} └── return a ) => Vector{Any} julia> code_typed(push!, (Vector{Any}, Any, Any)) 1-element Vector{Any}: CodeInfo( 1 ─ %1 = Base.arraylen(a)::Int64 │ $(Expr(:foreigncall, :(:jl_array_grow_end), Nothing, svec(Any, UInt64), 0, :(:ccall), Core.Argument(2), 0x0000000000000002, 0x0000000000000002))::Nothing └── goto #7 if not true 2 ┄ %4 = φ (#1 => 1, #6 => %14)::Int64 │ %5 = φ (#1 => 1, #6 => %15)::Int64 │ %6 = Base.getfield(x, %4, true)::Any │ %7 = Base.add_int(%1, %4)::Int64 │ Base.arrayset(true, a, %6, %7)::Vector{Any} │ %9 = (%5 === 2)::Bool └── goto #4 if not %9 3 ─ goto #5 4 ─ %12 = Base.add_int(%5, 1)::Int64 └── goto #5 5 ┄ %14 = φ (#4 => %12)::Int64 │ %15 = φ (#4 => %12)::Int64 │ %16 = φ (#3 => true, #4 => false)::Bool │ %17 = Base.not_int(%16)::Bool └── goto #7 if not %17 6 ─ goto #2 7 ┄ return a ) => Vector{Any} ``` This commit also adds the equivalent implementations for `pushfirst!`.

When calling `jl_error()` or `jl_errorf()`, we must check to see if we are so early in the bringup process that it is dangerous to attempt to construct a backtrace because the data structures used to provide line information are not properly setup. This can be easily triggered by running: ``` julia -C invalid ``` On an `i686-linux-gnu` build, this will hit the "Invalid CPU Name" branch in `jitlayers.cpp`, which calls `jl_errorf()`. This in turn calls `jl_throw()`, which will eventually call `jl_DI_for_fptr` as part of the backtrace printing process, which fails as the object maps are not fully initialized. See the below `gdb` stacktrace for details: ``` $ gdb -batch -ex 'r' -ex 'bt' --args ./julia -C invalid ... fatal: error thrown and no exception handler available. ErrorException("Invalid CPU name "invalid".") Thread 1 "julia" received signal SIGSEGV, Segmentation fault. 0xf75bd665 in std::_Rb_tree<unsigned int, std::pair<unsigned int const, JITDebugInfoRegistry::ObjectInfo>, std::_Select1st<std::pair<unsigned int const, JITDebugInfoRegistry::ObjectInfo> >, std::greater<unsigned int>, std::allocator<std::pair<unsigned int const, JITDebugInfoRegistry::ObjectInfo> > >::lower_bound (__k=<optimized out>, this=0x248) at /usr/local/i686-linux-gnu/include/c++/9.1.0/bits/stl_tree.h:1277 1277 /usr/local/i686-linux-gnu/include/c++/9.1.0/bits/stl_tree.h: No such file or directory. #0 0xf75bd665 in std::_Rb_tree<unsigned int, std::pair<unsigned int const, JITDebugInfoRegistry::ObjectInfo>, std::_Select1st<std::pair<unsigned int const, JITDebugInfoRegistry::ObjectInfo> >, std::greater<unsigned int>, std::allocator<std::pair<unsigned int const, JITDebugInfoRegistry::ObjectInfo> > >::lower_bound (__k=<optimized out>, this=0x248) at /usr/local/i686-linux-gnu/include/c++/9.1.0/bits/stl_tree.h:1277 #1 std::map<unsigned int, JITDebugInfoRegistry::ObjectInfo, std::greater<unsigned int>, std::allocator<std::pair<unsigned int const, JITDebugInfoRegistry::ObjectInfo> > >::lower_bound (__x=<optimized out>, this=0x248) at /usr/local/i686-linux-gnu/include/c++/9.1.0/bits/stl_map.h:1258 #2 jl_DI_for_fptr (fptr=4155049385, symsize=symsize@entry=0xffffcfa8, slide=slide@entry=0xffffcfa0, Section=Section@entry=0xffffcfb8, context=context@entry=0xffffcf94) at /cache/build/default-amdci5-4/julialang/julia-master/src/debuginfo.cpp:1181 #3 0xf75c056a in jl_getFunctionInfo_impl (frames_out=0xffffd03c, pointer=4155049385, skipC=0, noInline=0) at /cache/build/default-amdci5-4/julialang/julia-master/src/debuginfo.cpp:1210 #4 0xf7a6ca98 in jl_print_native_codeloc (ip=4155049385) at /cache/build/default-amdci5-4/julialang/julia-master/src/stackwalk.c:636 #5 0xf7a6cd54 in jl_print_bt_entry_codeloc (bt_entry=0xf0798018) at /cache/build/default-amdci5-4/julialang/julia-master/src/stackwalk.c:657 #6 jlbacktrace () at /cache/build/default-amdci5-4/julialang/julia-master/src/stackwalk.c:1090 #7 0xf7a3cd2b in ijl_no_exc_handler (e=0xf0794010) at /cache/build/default-amdci5-4/julialang/julia-master/src/task.c:605 #8 0xf7a3d10a in throw_internal (ct=ct@entry=0xf070c010, exception=<optimized out>, exception@entry=0xf0794010) at /cache/build/default-amdci5-4/julialang/julia-master/src/task.c:638 #9 0xf7a3d330 in ijl_throw (e=0xf0794010) at /cache/build/default-amdci5-4/julialang/julia-master/src/task.c:654 #10 0xf7a905aa in ijl_errorf (fmt=fmt@entry=0xf7647cd4 "Invalid CPU name \"%s\".") at /cache/build/default-amdci5-4/julialang/julia-master/src/rtutils.c:77 #11 0xf75a4b22 in (anonymous namespace)::createTargetMachine () at /cache/build/default-amdci5-4/julialang/julia-master/src/jitlayers.cpp:823 #12 JuliaOJIT::JuliaOJIT (this=<optimized out>) at /cache/build/default-amdci5-4/julialang/julia-master/src/jitlayers.cpp:1044 #13 0xf7531793 in jl_init_llvm () at /cache/build/default-amdci5-4/julialang/julia-master/src/codegen.cpp:8585 #14 0xf75318a8 in jl_init_codegen_impl () at /cache/build/default-amdci5-4/julialang/julia-master/src/codegen.cpp:8648 #15 0xf7a51a52 in jl_restore_system_image_from_stream (f=<optimized out>) at /cache/build/default-amdci5-4/julialang/julia-master/src/staticdata.c:2131 #16 0xf7a55c03 in ijl_restore_system_image_data (buf=0xe859c1c0 <jl_system_image_data> "8'\031\003", len=125161105) at /cache/build/default-amdci5-4/julialang/julia-master/src/staticdata.c:2184 #17 0xf7a55cf9 in jl_load_sysimg_so () at /cache/build/default-amdci5-4/julialang/julia-master/src/staticdata.c:424 #18 ijl_restore_system_image (fname=0x80a0900 "/build/bk_download/julia-d78fdad601/lib/julia/sys.so") at /cache/build/default-amdci5-4/julialang/julia-master/src/staticdata.c:2157 #19 0xf7a3bdfc in _finish_julia_init (rel=rel@entry=JL_IMAGE_JULIA_HOME, ct=<optimized out>, ptls=<optimized out>) at /cache/build/default-amdci5-4/julialang/julia-master/src/init.c:741 #20 0xf7a3c8ac in julia_init (rel=<optimized out>) at /cache/build/default-amdci5-4/julialang/julia-master/src/init.c:728 #21 0xf7a7f61d in jl_repl_entrypoint (argc=<optimized out>, argv=0xffffddf4) at /cache/build/default-amdci5-4/julialang/julia-master/src/jlapi.c:705 #22 0x080490a7 in main (argc=3, argv=0xffffddf4) at /cache/build/default-amdci5-4/julialang/julia-master/cli/loader_exe.c:59 ``` To prevent this, we simply avoid calling `jl_errorf` this early in the process, punting the problem to a later PR that can update guard conditions within `jl_error*`.

When calling `jl_error()` or `jl_errorf()`, we must check to see if we are so early in the bringup process that it is dangerous to attempt to construct a backtrace because the data structures used to provide line information are not properly setup. This can be easily triggered by running: ``` julia -C invalid ``` On an `i686-linux-gnu` build, this will hit the "Invalid CPU Name" branch in `jitlayers.cpp`, which calls `jl_errorf()`. This in turn calls `jl_throw()`, which will eventually call `jl_DI_for_fptr` as part of the backtrace printing process, which fails as the object maps are not fully initialized. See the below `gdb` stacktrace for details: ``` $ gdb -batch -ex 'r' -ex 'bt' --args ./julia -C invalid ... fatal: error thrown and no exception handler available. ErrorException("Invalid CPU name "invalid".") Thread 1 "julia" received signal SIGSEGV, Segmentation fault. 0xf75bd665 in std::_Rb_tree<unsigned int, std::pair<unsigned int const, JITDebugInfoRegistry::ObjectInfo>, std::_Select1st<std::pair<unsigned int const, JITDebugInfoRegistry::ObjectInfo> >, std::greater<unsigned int>, std::allocator<std::pair<unsigned int const, JITDebugInfoRegistry::ObjectInfo> > >::lower_bound (__k=<optimized out>, this=0x248) at /usr/local/i686-linux-gnu/include/c++/9.1.0/bits/stl_tree.h:1277 1277 /usr/local/i686-linux-gnu/include/c++/9.1.0/bits/stl_tree.h: No such file or directory. #0 0xf75bd665 in std::_Rb_tree<unsigned int, std::pair<unsigned int const, JITDebugInfoRegistry::ObjectInfo>, std::_Select1st<std::pair<unsigned int const, JITDebugInfoRegistry::ObjectInfo> >, std::greater<unsigned int>, std::allocator<std::pair<unsigned int const, JITDebugInfoRegistry::ObjectInfo> > >::lower_bound (__k=<optimized out>, this=0x248) at /usr/local/i686-linux-gnu/include/c++/9.1.0/bits/stl_tree.h:1277 #1 std::map<unsigned int, JITDebugInfoRegistry::ObjectInfo, std::greater<unsigned int>, std::allocator<std::pair<unsigned int const, JITDebugInfoRegistry::ObjectInfo> > >::lower_bound (__x=<optimized out>, this=0x248) at /usr/local/i686-linux-gnu/include/c++/9.1.0/bits/stl_map.h:1258 #2 jl_DI_for_fptr (fptr=4155049385, symsize=symsize@entry=0xffffcfa8, slide=slide@entry=0xffffcfa0, Section=Section@entry=0xffffcfb8, context=context@entry=0xffffcf94) at /cache/build/default-amdci5-4/julialang/julia-master/src/debuginfo.cpp:1181 #3 0xf75c056a in jl_getFunctionInfo_impl (frames_out=0xffffd03c, pointer=4155049385, skipC=0, noInline=0) at /cache/build/default-amdci5-4/julialang/julia-master/src/debuginfo.cpp:1210 #4 0xf7a6ca98 in jl_print_native_codeloc (ip=4155049385) at /cache/build/default-amdci5-4/julialang/julia-master/src/stackwalk.c:636 #5 0xf7a6cd54 in jl_print_bt_entry_codeloc (bt_entry=0xf0798018) at /cache/build/default-amdci5-4/julialang/julia-master/src/stackwalk.c:657 #6 jlbacktrace () at /cache/build/default-amdci5-4/julialang/julia-master/src/stackwalk.c:1090 #7 0xf7a3cd2b in ijl_no_exc_handler (e=0xf0794010) at /cache/build/default-amdci5-4/julialang/julia-master/src/task.c:605 #8 0xf7a3d10a in throw_internal (ct=ct@entry=0xf070c010, exception=<optimized out>, exception@entry=0xf0794010) at /cache/build/default-amdci5-4/julialang/julia-master/src/task.c:638 #9 0xf7a3d330 in ijl_throw (e=0xf0794010) at /cache/build/default-amdci5-4/julialang/julia-master/src/task.c:654 #10 0xf7a905aa in ijl_errorf (fmt=fmt@entry=0xf7647cd4 "Invalid CPU name \"%s\".") at /cache/build/default-amdci5-4/julialang/julia-master/src/rtutils.c:77 #11 0xf75a4b22 in (anonymous namespace)::createTargetMachine () at /cache/build/default-amdci5-4/julialang/julia-master/src/jitlayers.cpp:823 #12 JuliaOJIT::JuliaOJIT (this=<optimized out>) at /cache/build/default-amdci5-4/julialang/julia-master/src/jitlayers.cpp:1044 #13 0xf7531793 in jl_init_llvm () at /cache/build/default-amdci5-4/julialang/julia-master/src/codegen.cpp:8585 #14 0xf75318a8 in jl_init_codegen_impl () at /cache/build/default-amdci5-4/julialang/julia-master/src/codegen.cpp:8648 #15 0xf7a51a52 in jl_restore_system_image_from_stream (f=<optimized out>) at /cache/build/default-amdci5-4/julialang/julia-master/src/staticdata.c:2131 #16 0xf7a55c03 in ijl_restore_system_image_data (buf=0xe859c1c0 <jl_system_image_data> "8'\031\003", len=125161105) at /cache/build/default-amdci5-4/julialang/julia-master/src/staticdata.c:2184 #17 0xf7a55cf9 in jl_load_sysimg_so () at /cache/build/default-amdci5-4/julialang/julia-master/src/staticdata.c:424 #18 ijl_restore_system_image (fname=0x80a0900 "/build/bk_download/julia-d78fdad601/lib/julia/sys.so") at /cache/build/default-amdci5-4/julialang/julia-master/src/staticdata.c:2157 #19 0xf7a3bdfc in _finish_julia_init (rel=rel@entry=JL_IMAGE_JULIA_HOME, ct=<optimized out>, ptls=<optimized out>) at /cache/build/default-amdci5-4/julialang/julia-master/src/init.c:741 #20 0xf7a3c8ac in julia_init (rel=<optimized out>) at /cache/build/default-amdci5-4/julialang/julia-master/src/init.c:728 #21 0xf7a7f61d in jl_repl_entrypoint (argc=<optimized out>, argv=0xffffddf4) at /cache/build/default-amdci5-4/julialang/julia-master/src/jlapi.c:705 #22 0x080490a7 in main (argc=3, argv=0xffffddf4) at /cache/build/default-amdci5-4/julialang/julia-master/cli/loader_exe.c:59 ``` To prevent this, we simply avoid calling `jl_errorf` this early in the process, punting the problem to a later PR that can update guard conditions within `jl_error*`. (cherry picked from commit 21ab24e)

NHDaly added 8 commits October 7, 2021 10:37

Halfway through draft commit to construct full fieldpath from slot

ec1afc6

Account for inline-allocated structs in field path. Only partway done.

Start hooking up the field paths

64ac012

connect up the code from before (but it's still not working)

af589eb

maybe still need to do the off-by-one jameson mentioned? 🤔

Add debug logging for objects in Main module

ef9b34b

Fix silly mistake in slot accounting :)

5578921

It works now!! ``` - ga::Main.A @302073680 - b.y::Array{Any, 1} @302026704 ```

Clean up debug logs

6889aeb

Merge branch 'pv-heap-snapshot' into pv-heap-snapshot-slot-fieldpath

34b7ed7

Fixups, comments, todos

c5a20e7

NHDaly commented Oct 14, 2021

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vilterp approved these changes Oct 14, 2021

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NHDaly added 4 commits October 14, 2021 14:45

fix merge conflict

90984d7

Fix Tuple types in fieldpath_for_slot

da82125

Add TODO about overrunning type printing buffer

3fbd301

remove log

063b286

NHDaly merged commit 8a560cd into pv-heap-snapshot Oct 14, 2021

NHDaly deleted the pv-heap-snapshot-slot-fieldpath branch October 14, 2021 19:16

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Correctly compute field path for the heap snapshot, taking struct inlining into account#1

Correctly compute field path for the heap snapshot, taking struct inlining into account#1
NHDaly merged 12 commits intopv-heap-snapshotfrom
pv-heap-snapshot-slot-fieldpath

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