Can't debug executables that throw c++ exceptions

[ssbssa]

If you try to debug any executable that throws a c++ exception, you get this result (here with lldb):

* thread #​1, stop reason = Exception 0xc00000ff encountered at address 0x7fff44a181b0
  frame #​0: 0x00007fff44a181b0 ntdll.dll`RtlRaiseStatus + 32

I even tried cdb, and got a similar result.

After lots of searching I found this post detailing a deep analysis plus solution of the problem.

So I adapted this for gcc like this:

diff --git a/libgcc/unwind-seh.c b/libgcc/unwind-seh.c
index e13e3b2ef..43f038475 100644
--- a/libgcc/unwind-seh.c
+++ b/libgcc/unwind-seh.c
@@ -227,7 +227,7 @@ _GCC_specific_handler (PEXCEPTION_RECORD ms_exc, void *this_frame,
       if (ms_exc->ExceptionInformation[1] == (_Unwind_Ptr) this_frame)
        {
          RtlUnwindEx (this_frame, (PVOID) ms_exc->ExceptionInformation[2],
-                      ms_exc, gcc_exc, ms_orig_context,
+                      ms_exc, gcc_exc, ms_disp->ContextRecord,
                       ms_disp->HistoryTable);
          abort ();
        }
@@ -323,7 +323,7 @@ _GCC_specific_handler (PEXCEPTION_RECORD ms_exc, void *this_frame,
 
          /* Begin phase 2.  Perform the unwinding.  */
          RtlUnwindEx (this_frame, (PVOID)gcc_context.ra, ms_exc,
-                      (PVOID)gcc_context.reg[0], ms_orig_context,
+                      (PVOID)gcc_context.reg[0], ms_disp->ContextRecord,
                       ms_disp->HistoryTable);
        }
 

And now I can debug successfully.

[ssbssa]

The patch above doesn't fix exceptions for me completely in a real program.
While the 0xc00000ff exception no longer happens, some variables/registers are loosing their correct values when an exception is caught.

Here it's about variable i of ada_decode, which should be stored in register x26.
At the point of the throw, it still has value 63:

(lldb) display $x26
Stop hook #1 added.
(lldb) c
Process 2272 resuming
(unsigned long long) $0 = 1429099593744
Process 2272 stopped
* thread #1, stop reason = breakpoint 5.11
    frame #0: 0x00007ff6172e7260 gdb.exe`__cxxabiv1::__cxa_throw(obj=0x0000014c9e635fc0, tinfo=0x00007ff6176160d8, dest=(gdb.exe`gdb_exception_error::~gdb_exception_error() at shared_ptr_base.h:1069:7)) at eh_throw.cc:80:1
(lldb) bt
* thread #1, stop reason = breakpoint 5.11
  * frame #0: 0x00007ff6172e7260 gdb.exe`__cxxabiv1::__cxa_throw(obj=0x0000014c9e635fc0, tinfo=0x00007ff6176160d8, dest=(gdb.exe`gdb_exception_error::~gdb_exception_error() at shared_ptr_base.h:1069:7)) at eh_throw.cc:80:1
    frame #1: 0x00007ff6172eec50 gdb.exe`throw_verror(errors, char const*, std::__va_list) [inlined] throw_it(reason=RETURN_ERROR, error=GENERIC_ERROR, fmt=<unavailable>, ap=(__stack = 0x0000001bf05fece0, __gr_top = 0x0000001bf05fece0, __vr_top = 0x0000001bf05feca0, __gr_offs = -56, __vr_offs = -128)) at common-exceptions.cc:203:46
    frame #2: 0x00007ff6172eec04 gdb.exe`throw_verror(error=GENERIC_ERROR, fmt="Could not convert character to `%s' character set", ap=<unavailable>) at common-exceptions.cc:211:12
    frame #3: 0x00007ff617038f50 gdb.exe`verror(string=<unavailable>, args=<unavailable>) at utils.c:196:16
    frame #4: 0x00007ff6171ab4a8 gdb.exe`error(fmt=<unavailable>) at errors.cc:45:1
    frame #5: 0x00007ff616da19b8 gdb.exe`convert_between_encodings(from=<unavailable>, to="CP1252", bytes=<unavailable>, num_bytes=<unavailable>, width=4, output=0x0000001bf05fedc8, translit=translit_none) at charset.c:548:5
    frame #6: 0x00007ff616d17604 gdb.exe`convert_from_hex_encoded(out="?do_out@?$codecvt@_WDU_Mbstatet@@@std@@MEBAHAEAU_Mbstatet@@PEB_", str="1AEAPEB_WPEAD3AEAPEAD@Z", n=4) at ada-lang.c:1294:2
    frame #7: 0x00007ff616d1b4b4 gdb.exe`ada_decode[abi:cxx11](encoded="?do_out@?$codecvt@_WDU_Mbstatet@@@std@@MEBAHAEAU_Mbstatet@@PEB_W1AEAPEB_WPEAD3AEAPEAD@Z", wrap=true, operators=true, wide=true) at ada-lang.c:1518:4
    frame #8: 0x00007ff6172aa858 gdb.exe`ada_language::sniff_from_mangled_name(this=<unavailable>, mangled="?do_out@?$codecvt@_WDU_Mbstatet@@@std@@MEBAHAEAU_Mbstatet@@PEB_W1AEAPEB_WPEAD3AEAPEAD@Z", out=nullptr) const at ada-lang.c:13526:8
    frame #9: 0x00007ff616fd6aa4 gdb.exe`symbol_find_demangled_name(gsymbol=0x0000014cb66c8180, mangled="?do_out@?$codecvt@_WDU_Mbstatet@@@std@@MEBAHAEAU_Mbstatet@@PEB_W1AEAPEB_WPEAD3AEAPEAD@Z") at symtab.c:980:7
    frame #10: 0x00007ff616f213b0 gdb.exe`minimal_symbol_reader::install(this=0x0000001bf05ff200) at minsyms.c:1495:6
    frame #11: 0x00007ff616dbecd0 gdb.exe`coff_symfile_read(objfile=0x0000014cb24ffb40, symfile_flags=<unavailable>) at coffread.c:647:3
    frame #12: 0x00007ff616fcf354 gdb.exe`read_symbols(objfile=0x0000014cb24ffb40, add_flags=(m_enum_value = SYMFILE_DEFER_BP_RESET)) at symfile.c:764:18
    frame #13: 0x00007ff616fcec40 gdb.exe`symbol_file_add_with_addrs(abfd=<unavailable>, name="C:\\Windows\\System32\\msvcp_win.dll", add_flags=<unavailable>, addrs=<unavailable>, flags=<unavailable>, parent=<unavailable>) at symfile.c:963:3
    frame #14: 0x00007ff616f9ebd4 gdb.exe`solib_read_symbols(so=0x0000014cb88ed2f0, flags=(m_enum_value = SYMFILE_DEFER_BP_RESET)) at solib.c:660:7
    frame #15: 0x00007ff616fa0aa0 gdb.exe`solib_add(pattern=0x0000000000000000, from_tty=0, readsyms=1) at solib.c:993:13
    frame #16: 0x00007ff616eb5bbc gdb.exe`post_create_inferior(from_tty=0, set_pspace_solib_ops=true) at infcmd.c:298:6
    frame #17: 0x00007ff616eb6a6c gdb.exe`run_command_1(args=<unavailable>, from_tty=<unavailable>, run_how=RUN_STOP_AT_MAIN) at infcmd.c:492:24
    frame #18: 0x00007ff616dac754 gdb.exe`cmd_func(cmd=<unavailable>, args=<unavailable>, from_tty=<unavailable>) at cli-decode.c:2827:17
    frame #19: 0x00007ff61702029c gdb.exe`execute_command(p=<unavailable>, from_tty=1) at top.c:577:2
    frame #20: 0x00007ff616e6a014 gdb.exe`command_handler(command="") at event-top.c:613:7
    frame #21: 0x00007ff616e6b758 gdb.exe`command_line_handler(rl=<unavailable>) at event-top.c:849:7
    frame #22: 0x00007ff616e6aba8 gdb.exe`gdb_rl_callback_handler(rl="start") at event-top.c:288:56
    frame #23: 0x00007ff617089dc0 gdb.exe`rl_callback_read_char at callback.c:302:6
    frame #24: 0x00007ff616e6acfc gdb.exe`::gdb_rl_callback_read_char_wrapper_sjlj() at event-top.c:197:7
    frame #25: 0x00007ff616e6aea4 gdb.exe`gdb_rl_callback_read_char_wrapper(client_data=<unavailable>) at event-top.c:240:1
    frame #26: 0x00007ff617037728 gdb.exe`stdin_event_handler(error=<unavailable>, client_data=0x0000014c9e10a0b0) at ui.c:154:4
    frame #27: 0x00007ff6171abb98 gdb.exe`gdb_wait_for_event(block=<unavailable>) at event-loop.cc:551:7
    frame #28: 0x00007ff6171ac520 gdb.exe`gdb_do_one_event(mstimeout=-1) at event-loop.cc:571:20
    frame #29: 0x00007ff616ef68d4 gdb.exe`::captured_command_loop() at interps.h:87:29
    frame #30: 0x00007ff616ef9f4c gdb.exe`gdb_main(args=0x0000001bf05ffc40) at main.c:1384:4
    frame #31: 0x00007ff6172e7544 gdb.exe`main(argc=3, argv=0x0000014c9e116c80) at gdb.c:38:3
    frame #32: 0x00007ff616d01420 gdb.exe`__tmainCRTStartup + 888
    frame #33: 0x00007ff616d01090 gdb.exe`.l_start + 16
    frame #34: 0x00007ffe568f8740 kernel32.dll`BaseThreadInitThunk + 64
(lldb) up
frame #1: 0x00007ff6172eec50 gdb.exe`throw_verror(errors, char const*, std::__va_list) [inlined] throw_it(reason=RETURN_ERROR, error=GENERIC_ERROR, fmt=<unavailable>, ap=(__stack = 0x0000001bf05fece0, __gr_top = 0x0000001bf05fece0, __vr_top = 0x0000001bf05feca0, __gr_offs = -56, __vr_offs = -128)) at common-exceptions.cc:203:46
(lldb)
frame #2: 0x00007ff6172eec04 gdb.exe`throw_verror(error=GENERIC_ERROR, fmt="Could not convert character to `%s' character set", ap=<unavailable>) at common-exceptions.cc:211:12
(lldb)
frame #3: 0x00007ff617038f50 gdb.exe`verror(string=<unavailable>, args=<unavailable>) at utils.c:196:16
(lldb)
frame #4: 0x00007ff6171ab4a8 gdb.exe`error(fmt=<unavailable>) at errors.cc:45:1
(lldb)
frame #5: 0x00007ff616da19b8 gdb.exe`convert_between_encodings(from=<unavailable>, to="CP1252", bytes=<unavailable>, num_bytes=<unavailable>, width=4, output=0x0000001bf05fedc8, translit=translit_none) at charset.c:548:5
(lldb)
frame #6: 0x00007ff616d17604 gdb.exe`convert_from_hex_encoded(out="?do_out@?$codecvt@_WDU_Mbstatet@@@std@@MEBAHAEAU_Mbstatet@@PEB_", str="1AEAPEB_WPEAD3AEAPEAD@Z", n=4) at ada-lang.c:1294:2
(lldb)
frame #7: 0x00007ff616d1b4b4 gdb.exe`ada_decode[abi:cxx11](encoded="?do_out@?$codecvt@_WDU_Mbstatet@@@std@@MEBAHAEAU_Mbstatet@@PEB_W1AEAPEB_WPEAD3AEAPEAD@Z", wrap=true, operators=true, wide=true) at ada-lang.c:1518:4
(lldb) p i
(int) 63
(lldb) p $x26
(lldb) (unsigned long long) 63

But when the same exception is caught, i suddenly has the value -1124515824:

(lldb) c
Process 2272 resuming
(unsigned long long) $1 = 1429099593744
Process 2272 stopped
* thread #1, stop reason = breakpoint 5.10
    frame #0: 0x00007ff6172e6a20 gdb.exe`__cxxabiv1::__cxa_begin_catch(exc_obj_in=0x0000014c9e635f80) at eh_catch.cc:41:1
(lldb) bt
* thread #1, stop reason = breakpoint 5.10
  * frame #0: 0x00007ff6172e6a20 gdb.exe`__cxxabiv1::__cxa_begin_catch(exc_obj_in=0x0000014c9e635f80) at eh_catch.cc:41:1
    frame #1: 0x00007ff616d17680 gdb.exe`convert_from_hex_encoded(out="Bl\xff\U00000017\U0000001f \U00000003\xd5\U0000001f \U00000003\xd5a\xd6\U00000005", str="1AEAPEB_WPEAD3AEAPEAD@Z", n=4) at ada-lang.c:1301:3
    frame #2: 0x00007ff616d1b4b4 gdb.exe`ada_decode[abi:cxx11](encoded="?do_out@?$codecvt@_WDU_Mbstatet@@@std@@MEBAHAEAU_Mbstatet@@PEB_W1AEAPEB_WPEAD3AEAPEAD@Z", wrap=true, operators=true, wide=true) at ada-lang.c:1518:4
    frame #3: 0x00007ff6172aa858 gdb.exe`ada_language::sniff_from_mangled_name(this=<unavailable>, mangled="?do_out@?$codecvt@_WDU_Mbstatet@@@std@@MEBAHAEAU_Mbstatet@@PEB_W1AEAPEB_WPEAD3AEAPEAD@Z", out=nullptr) const at ada-lang.c:13526:8
    frame #4: 0x00007ff616fd6aa4 gdb.exe`symbol_find_demangled_name(gsymbol=0x0000014cb66c8180, mangled="?do_out@?$codecvt@_WDU_Mbstatet@@@std@@MEBAHAEAU_Mbstatet@@PEB_W1AEAPEB_WPEAD3AEAPEAD@Z") at symtab.c:980:7
    frame #5: 0x00007ff616f213b0 gdb.exe`minimal_symbol_reader::install(this=0x0000001bf05ff200) at minsyms.c:1495:6
    frame #6: 0x00007ff616dbecd0 gdb.exe`coff_symfile_read(objfile=0x0000014cb24ffb40, symfile_flags=<unavailable>) at coffread.c:647:3
    frame #7: 0x00007ff616fcf354 gdb.exe`read_symbols(objfile=0x0000014cb24ffb40, add_flags=(m_enum_value = SYMFILE_DEFER_BP_RESET)) at symfile.c:764:18
    frame #8: 0x00007ff616fcec40 gdb.exe`symbol_file_add_with_addrs(abfd=<unavailable>, name="C:\\Windows\\System32\\msvcp_win.dll", add_flags=<unavailable>, addrs=<unavailable>, flags=<unavailable>, parent=<unavailable>) at symfile.c:963:3
    frame #9: 0x00007ff616f9ebd4 gdb.exe`solib_read_symbols(so=0x0000014cb88ed2f0, flags=(m_enum_value = SYMFILE_DEFER_BP_RESET)) at solib.c:660:7
    frame #10: 0x00007ff616fa0aa0 gdb.exe`solib_add(pattern=0x0000000000000000, from_tty=0, readsyms=1) at solib.c:993:13
    frame #11: 0x00007ff616eb5bbc gdb.exe`post_create_inferior(from_tty=0, set_pspace_solib_ops=true) at infcmd.c:298:6
    frame #12: 0x00007ff616eb6a6c gdb.exe`run_command_1(args=<unavailable>, from_tty=<unavailable>, run_how=RUN_STOP_AT_MAIN) at infcmd.c:492:24
    frame #13: 0x00007ff616dac754 gdb.exe`cmd_func(cmd=<unavailable>, args=<unavailable>, from_tty=<unavailable>) at cli-decode.c:2827:17
    frame #14: 0x00007ff61702029c gdb.exe`execute_command(p=<unavailable>, from_tty=1) at top.c:577:2
    frame #15: 0x00007ff616e6a014 gdb.exe`command_handler(command="") at event-top.c:613:7
    frame #16: 0x00007ff616e6b758 gdb.exe`command_line_handler(rl=<unavailable>) at event-top.c:849:7
    frame #17: 0x00007ff616e6aba8 gdb.exe`gdb_rl_callback_handler(rl="start") at event-top.c:288:56
    frame #18: 0x00007ff617089dc0 gdb.exe`rl_callback_read_char at callback.c:302:6
    frame #19: 0x00007ff616e6acfc gdb.exe`::gdb_rl_callback_read_char_wrapper_sjlj() at event-top.c:197:7
    frame #20: 0x00007ff616e6aea4 gdb.exe`gdb_rl_callback_read_char_wrapper(client_data=<unavailable>) at event-top.c:240:1
    frame #21: 0x00007ff617037728 gdb.exe`stdin_event_handler(error=<unavailable>, client_data=0x0000014c9e10a0b0) at ui.c:154:4
    frame #22: 0x00007ff6171abb98 gdb.exe`gdb_wait_for_event(block=<unavailable>) at event-loop.cc:551:7
    frame #23: 0x00007ff6171ac520 gdb.exe`gdb_do_one_event(mstimeout=-1) at event-loop.cc:571:20
    frame #24: 0x00007ff616ef68d4 gdb.exe`::captured_command_loop() at interps.h:87:29
    frame #25: 0x00007ff616ef9f4c gdb.exe`gdb_main(args=0x0000001bf05ffc40) at main.c:1384:4
    frame #26: 0x00007ff6172e7544 gdb.exe`main(argc=3, argv=0x0000014c9e116c80) at gdb.c:38:3
    frame #27: 0x00007ff616d01420 gdb.exe`__tmainCRTStartup + 888
    frame #28: 0x00007ff616d01090 gdb.exe`.l_start + 16
    frame #29: 0x00007ffe568f8740 kernel32.dll`BaseThreadInitThunk + 64
(lldb) up
frame #1: 0x00007ff616d17680 gdb.exe`convert_from_hex_encoded(out="Bl\xff\U00000017\U0000001f \U00000003\xd5\U0000001f \U00000003\xd5a\xd6\U00000005", str="1AEAPEB_WPEAD3AEAPEAD@Z", n=4) at ada-lang.c:1301:3
(lldb)
frame #2: 0x00007ff616d1b4b4 gdb.exe`ada_decode[abi:cxx11](encoded="?do_out@?$codecvt@_WDU_Mbstatet@@@std@@MEBAHAEAU_Mbstatet@@PEB_W1AEAPEB_WPEAD3AEAPEAD@Z", wrap=true, operators=true, wide=true) at ada-lang.c:1518:4
(lldb) p i
(int) -1124515824

When finally returning to ada_decode, it still has the wrong value:

(lldb) c
Process 2272 resuming
(unsigned long long) $2 = 1429099593744
Process 2272 stopped
* thread #1, stop reason = breakpoint 4.4
    frame #0: 0x00007ff616d17680 gdb.exe`convert_from_hex_encoded(out="Bl\xff\U00000017\U0000001f \U00000003\xd5\U0000001f \U00000003\xd5a\xd6\U00000005", str=<unavailable>, n=4) at ada-lang.c:1306:7
(lldb) fin
(unsigned long long) $11 = 1429099593744
Process 2272 stopped
* thread #1, stop reason = step out
Return value: (bool) $10 = false

    frame #0: 0x00007ff616d1b4b4 gdb.exe`ada_decode[abi:cxx11](encoded="?do_out@?$codecvt@_WDU_Mbstatet@@@std@@MEBAHAEAU_Mbstatet@@PEB_W1AEAPEB_WPEAD3AEAPEAD@Z", wrap=true, operators=true, wide=true) at ada-lang.c:1518:33
(lldb) p i
(int) -1124515824

I'm a bit out of my depth here, my only guess would be that it has something to do with unwinding.