https://issues.dlang.org/show_bug.cgi?id=21919

Iain Buclaw <ibuclaw@gdcproject.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ibuclaw@gdcproject.org

--- Comment #1 from Iain Buclaw <ibuclaw@gdcproject.org> ---
Confirmed on DMD when running the unittests.

generated/osx/release/64/unittest/test_runner core.thread.threadgroup
make[1]: *** [generated/osx/release/64/unittest/core/thread/fiber] Bus error:
10
make[1]: *** Deleting file
`generated/osx/release/64/unittest/core/thread/fiber'
make[1]: *** Waiting for unfinished jobs....
generated/osx/release/64/unittest/test_runner core.thread.types
make: *** [unittest-release] Error 2

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https://issues.dlang.org/show_bug.cgi?id=21919

--- Comment #2 from Iain Buclaw <ibuclaw@gdcproject.org> ---
$ sw_vers
ProductName:    macOS
ProductVersion: 11.1
BuildVersion:   20C69

$ clang --version
Apple clang version 12.0.0 (clang-1200.0.32.27)

$ xcodebuild -version
Xcode 12.2
Build version 12B45b

$ uname -v
Darwin Kernel Version 20.2.0: Wed Dec  2 20:39:59 PST 2020;
root:xnu-7195.60.75~1/RELEASE_X86_64

druntime: a79bb0eb0424f77159eb72e1c527db3b2ae2a57d

dmd: 97aa2ae5ee19ce6a2979ca1627479df713f99252

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https://issues.dlang.org/show_bug.cgi?id=21919

--- Comment #3 from Iain Buclaw <ibuclaw@gdcproject.org> ---
Process 65900 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS
(code=2, address=0x100c8cc70)
    frame #0: 0x00007fff203794e0 libsystem_pthread.dylib`___chkstk_darwin + 96
libsystem_pthread.dylib`___chkstk_darwin:
->  0x7fff203794e0 <+96>:  testq  %rcx, (%rcx)
    0x7fff203794e3 <+99>:  popq   %rcx
    0x7fff203794e4 <+100>: retq
libsystem_pthread.dylib`pthread_getspecific:
    0x7fff203794e5 <+0>:   movq   %gs:(,%rdi,8), %rax
Target 0: (test_runner) stopped.
(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS
(code=2, address=0x100c8cc70)
  * frame #0: 0x00007fff203794e0 libsystem_pthread.dylib`___chkstk_darwin + 96
    frame #1: 0x00007fff20379480 libsystem_pthread.dylib`thread_start + 20
    frame #2: 0x00007fff2a542a9c
libunwind.dylib`libunwind::UnwindCursor<libunwind::LocalAddressSpace,
libunwind::Registers_x86_64>::step() + 476
    frame #3: 0x00007fff2a5446ee libunwind.dylib`_Unwind_RaiseException + 189
    frame #4: 0x00000001001bbeb8 test_runner`_d_throwdwarf at dwarfeh.d:317
    frame #5: 0x0000000100188b84
test_runner`_D4core6thread5fiber19__unittest_L1679_C1FZ9__lambda1MFNaNbNfZv at
fiber.d:1686
    frame #6: 0x000000010018fb85
test_runner`_D4core6thread7context8Callable6opCallMFZv at context.d:46
    frame #7: 0x0000000100187ac5 test_runner`_D4core6thread5fiber5Fiber3runMFZv
at fiber.d:869
    frame #8: 0x000000010018749f test_runner`fiber_entryPoint at fiber.d:157

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https://issues.dlang.org/show_bug.cgi?id=21919

--- Comment #4 from Iain Buclaw <ibuclaw@gdcproject.org> ---
This was discovered in December, hence the git commit hashes are 5 months old.

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https://issues.dlang.org/show_bug.cgi?id=21919

--- Comment #5 from Iain Buclaw <ibuclaw@gdcproject.org> ---
To describe what looks like is happening:

1. A D fiber context switch occurs.
2. An exception is thrown.
3. libunwind's entry point for raising exceptions is called.
4. Segfault somewhere deep in libc/pthread.

The unittest block that matches the encoded line numbers in the function name is:
---
// Test exception handling inside fibers.
unittest
{
    enum MSG = "Test message.";
    string caughtMsg;
    (new Fiber({
        try
        {
            throw new Exception(MSG);
        }
        catch (Exception e)
        {
            caughtMsg = e.msg;
        }
    })).call();
    assert(caughtMsg == MSG);
}

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https://issues.dlang.org/show_bug.cgi?id=21919

Lionello Lunesu <lio+bugzilla@lunesu.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |lio+bugzilla@lunesu.com

--- Comment #6 from Lionello Lunesu <lio+bugzilla@lunesu.com> ---
I suspect I'm running into this same bug while running the DMD 2.097.2 test suite on Big Sur:

$ test_results/runnable/test15779_0
fish: “test_results/runnable/test15779…” terminated by signal SIGBUS
(Misaligned address error)

$ lldb test_results/runnable/test15779_0
(lldb) target create "test_results/runnable/test15779_0"
Current executable set to
'/Users/llunesu/repos/d/dmd/test/test_results/runnable/test15779_0' (x86_64).
(lldb) r
Process 854 launched:
'/Users/llunesu/repos/d/dmd/test/test_results/runnable/test15779_0' (x86_64)
Process 854 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS
(code=2, address=0x1001edc60)
    frame #0: 0x00007fff2031b4a8 libsystem_pthread.dylib`___chkstk_darwin + 96
libsystem_pthread.dylib`___chkstk_darwin:
->  0x7fff2031b4a8 <+96>:  testq  %rcx, (%rcx)
    0x7fff2031b4ab <+99>:  popq   %rcx
    0x7fff2031b4ac <+100>: retq

libsystem_pthread.dylib`pthread_getspecific:
    0x7fff2031b4ad <+0>:   movq   %gs:(,%rdi,8), %rax
Target 0: (test15779_0) stopped.
(lldb)

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https://issues.dlang.org/show_bug.cgi?id=21919

--- Comment #7 from Lionello Lunesu <lio+bugzilla@lunesu.com> ---
Stack trace for previous crash:

(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS
(code=2, address=0x1001e9c60)
  * frame #0: 0x00007fff2031b4a8 libsystem_pthread.dylib`___chkstk_darwin + 96
    frame #1: 0x00007fff2031b448 libsystem_pthread.dylib`thread_start + 20
    frame #2: 0x00007fff2a4bfb2d
libunwind.dylib`libunwind::UnwindCursor<libunwind::LocalAddressSpace,
libunwind::Registers_x86_64>::getInfoFromDwarfSection(unsigned long,
libunwind::UnwindInfoSections const&, unsigned int) + 191
    frame #3: 0x00007fff2a4bfa01
libunwind.dylib`libunwind::UnwindCursor<libunwind::LocalAddressSpace,
libunwind::Registers_x86_64>::setInfoBasedOnIPRegister(bool) + 999
    frame #4: 0x00007fff2a4c1ec9
libunwind.dylib`libunwind::UnwindCursor<libunwind::LocalAddressSpace,
libunwind::Registers_x86_64>::step() + 461
    frame #5: 0x00007fff2a4c3a18 libunwind.dylib`_Unwind_RaiseException + 189
    frame #6: 0x000000010002fca5 test15779_0`_d_throwdwarf + 185
    frame #7: 0x0000000100002410
test15779_0`_D9test157793barFZ9__lambda1FNaNfZv + 80
    frame #8: 0x000000010002cc2f
test15779_0`_D4core6thread7context8Callable6opCallMFZv + 27
    frame #9: 0x00000001000293a7 test15779_0`fiber_entryPoint + 99

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https://issues.dlang.org/show_bug.cgi?id=21919

--- Comment #8 from Lionello Lunesu <lio+bugzilla@lunesu.com> ---
$ sw_vers
ProductName:    macOS
ProductVersion: 11.5.2
BuildVersion:   20G95

$ clang --version
Apple clang version 12.0.5 (clang-1205.0.22.11)
Target: x86_64-apple-darwin20.6.0
Thread model: posix
InstalledDir:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

$ xcodebuild -version
Xcode 12.5.1
Build version 12E507

$ uname -v
Darwin Kernel Version 20.6.0: Wed Jun 23 00:26:31 PDT 2021;
root:xnu-7195.141.2~5/RELEASE_X86_64

dmd, druntime, Phobos: tag v2.097.2

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https://issues.dlang.org/show_bug.cgi?id=21919

Lionello Lunesu <lio+bugzilla@lunesu.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://issues.dlang.org/sh
                   |                            |ow_bug.cgi?id=15779

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https://issues.dlang.org/show_bug.cgi?id=21919

--- Comment #9 from Iain Buclaw <ibuclaw@gdcproject.org> ---
Done some prodding around, and the root cause is darwin's libunwind now overflows the Fiber's small 16kb stack.

Fix then is to bump the stack allocated for Fibers.

     version (Windows)
         // exception handling walks the stack, invoking DbgHelp.dll which
         // needs up to 16k of stack space depending on the version of
DbgHelp.dll,
         // the existence of debug symbols and other conditions. Avoid causing
         // stack overflows by defaulting to a larger stack size
         enum defaultStackPages = 8;
+    else version (OSX)
+    {
+        version (X86_64)
+            enum defaultStackPages = 8;
+        else
+            enum defaultStackPages = 4;
+    }
     else
         enum defaultStackPages = 4;

Darwin x86 pagesize is 4k, whilst arm64 is 16k, so this fix should only be applied to 64-bit code.

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