On Wed, Aug 9, 2023 at 10:05 AM Jean-Claude Monnin <jc_mon...@emailplus.org>
wrote:
> I've tried to figure out a bit more what is going on by adding prints
> along the call stack. It looks like it's the `base::CallOnce` in
> `code-range.cc` introduced in commit 26bc8bb4 that is the problem. Here the
> code with the added prints:
> V8_DECLARE_ONCE(init_code_range_once);
> void InitProcessWideCodeRange(v8::PageAllocator* page_allocator,
> size_t requested_size) {
> i::PrintF(stdout, "InitProcessWideCodeRange %u\n", requested_size);
> CodeRange* code_range = new CodeRange();
> if (!code_range->InitReservation(page_allocator, requested_size)) {
> V8::FatalProcessOutOfMemory(
> nullptr, "Failed to reserve virtual memory for CodeRange");
> }
> process_wide_code_range_ = code_range;
> #ifdef V8_EXTERNAL_CODE_SPACE
> #ifdef V8_COMPRESS_POINTERS_IN_SHARED_CAGE
> ExternalCodeCompressionScheme::InitBase(
> ExternalCodeCompressionScheme::PrepareCageBaseAddress(
> code_range->base()));
> #endif // V8_COMPRESS_POINTERS_IN_SHARED_CAGE
> #endif // V8_EXTERNAL_CODE_SPACE
> }
> } // namespace
>
> // static
> CodeRange* CodeRange::EnsureProcessWideCodeRange(
> v8::PageAllocator* page_allocator, size_t requested_size) {
> i::PrintF(stdout, "CodeRange::EnsureProcessWideCodeRange %u\n",
> requested_size);
> base::CallOnce(&init_code_range_once, InitProcessWideCodeRange,
> page_allocator, requested_size);
> return process_wide_code_range_;
> }
>
> It outputs:
> CodeRange::EnsureProcessWideCodeRange 536870912
> InitProcessWideCodeRange 2034756544 <(203)%20475-6544>
>
> It looks like the `requested_size` isn't forwarded correctly in
> `base::CallOnce`.
> I'm not sure to understand the CallOnce implementation, but I wonder if
> calling `std::function<void()>` with `init_func(args...)` isn't undefined
> behavior. Not sure how to fix/work around.
>
Which part would be undefined behavior? From a quick glance, the CallOnce
implementation
<https://source.chromium.org/chromium/chromium/src/+/refs/heads/main:v8/src/base/once.h;l=101;drc=a9163a67bbe920dfcfa6286bf0d172a1af377dba>
looks
reasonable to me. It sounds like something around the lambda
capture-by-copy is buggy (accessing the wrong stack slot?). Perhaps you can
verify with disassembly of InitProcessWideCodeRange, or step through and
find out what it's actually copying.
>
> On Wed, Aug 9, 2023, at 8:03 AM, Jakob Gruber wrote:
>
>
>
> On Tue, Aug 8, 2023 at 3:20 PM Jean-Claude Monnin <jc_mon...@emailplus.org>
> wrote:
>
>
> Hi Jakob,
>
> Thanks for your reply.
> It looks like using Microsoft's C++ library instead of libc++ is somewhat
> exotic for v8. Unfortunately there are cases where it's almost impossible
> to switch to libc++.
>
> Since I have a chance to get some feedback here of how to address this
> issue, I'm going to try to give you as much info as possible.
>
> `mksnapshot.exe` aborts at `VirtualMemoryCage::InitReservation` at
> following check:
> CHECK(IsAligned(params.reservation_size, allocate_page_size));
>
> When adding following print on the line before
> i::PrintF(stdout, "VirtualMemoryCage::InitReservation %u %u\n",
> params.reservation_size, allocate_page_size);
> it prints
> VirtualMemoryCage::InitReservation 3356617664 65536
> It looks like the supplied `params.reservation_size` is not aligned.
>
>
> Thanks for the investigation, very helpful. I wonder where that
> reservation_size comes from. It doesn't look like any value we'd set in V8.
> Corrupted? Uninitialized?
>
> I'd expect it to be set by mksnapshot here
> <https://source.chromium.org/chromium/chromium/src/+/refs/heads/main:v8/src/snapshot/mksnapshot.cc;l=282;drc=a9163a67bbe920dfcfa6286bf0d172a1af377dba>
> and
> picked up by isolate initialization here
> <https://source.chromium.org/chromium/chromium/src/+/refs/heads/main:v8/src/heap/heap.cc;l=5420;drc=a9163a67bbe920dfcfa6286bf0d172a1af377dba>.
> There it should either be some reasonable aligned value, or 0 and we'd fall
> back to kMaximalCodeRangeSize.
>
>
>
>
> Full call stack is included in screenshot below (sorry for the screenshot,
> I couldn't find a way to copy text from WinDbg)
>
> I'm happy to investigate further, but wanted to send this out in case
> there is anything specific that would be helpful.
>
> Jean-Claude
>
> On Tue, Aug 8, 2023, at 12:13 PM, Jakob Gruber wrote:
>
> Hi Jean-Claude,
>
> no, we don't have a lot of test coverage for `use_custom_libcxx=false`,
> this mode is only supported on a best-effort basis.
>
> For debugging: a backtrace and symbols would be useful. Does running
> `mksnapshot` in a debugger give more infos? Also, a bisect to find the
> culprit change would be very helpful.
>
> On Thu, Aug 3, 2023 at 6:54 PM Jean-Claude Monnin <jc_mon...@emailplus.org>
> wrote:
>
> Hi,
>
> On windows, the v8 version 11.5 build fails when generating the snapshot
> with following error:
>
>
> C:/Users/jean-claude/Documents/src/google/depot_tools/bootstrap-2@3_8_10_chromium_26_bin/python3/bin/python3.exe
> ../../tools/run.py ./mksnapshot --turbo_instruction_scheduling
> --target_os=win --target_arch=x64 --embedded_src gen/embedded.S
> --embedded_variant Default --random-seed 314159265 --startup_blob
> snapshot_blob.bin --no-native-code-counters
> Return code is 2147483651 <(214)%20748-3651>
>
> These are the options used (args.gn):
> is_official_build = true
> target_cpu = "x64"
> is_component_build = true
> use_custom_libcxx = false
> chrome_pgo_phase = false
> treat_warnings_as_errors = false
> fatal_linker_warnings = false
> symbol_level = 0
>
> When using `is_debug=false` instead of `is_official_build = true` it
> builds fine, but it comes with performance regressions compared to older
> version 9.3 build with `is_official_build = true`.
>
> If using either `is_component_build = false` or `use_custom_libcxx =
> true`, it builds fine too, however it's not really an option as I need a
> dll build and I need to use Microsoft's C++ standard library because third
> party dependencies prevents us to use libc++.
>
> I also tried version 11.4 and 11.6 and they give the same error.
>
> Any hints in how to diagnose/fix that would be appreciated.
>
> Auxiliary question: Is any big project using `use_custom_libcxx = false`
> (eg. Microsoft's C++ standard library), or is this untested?
> Chrome/node/deno all use libc++?
>
> Best regards,
> Jean-Claude
>
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