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IDProjectCategoryView StatusLast Update
0035639FPCRTLpublic2020-11-24 06:27
ReporterCyrax Assigned To 
Status newResolutionopen 
PlatformLinux x86_64OSArch 
Product Version3.3.1 
Summary0035639: [doublecommander] Getting SIGSEGV during normal string concat operation at program startup.
//#0 fpc_ansistr_concat(0x0, 0xdd92c0 'AddPoll ', 0x18cb6d0 '21', 0) at ../inc/
// local variables
S1='AddPoll '

Somehow at this point, Length function gives string S2 wrong value. And further down the execution path, SetLength tries to allocate absurd amount memory for new string thus causing SIGSEGV to happen.
Additional InformationProject Double Commander raised exception class 'External: SIGSEGV'.

 In file '../inc/' at line 779:

#0 fpc_ansistr_setlength(0x0, 281474976710666, 65001) at ../inc/
0000001 fpc_ansistr_concat(0x0, 0xdd92c0 'AddPoll ', 0x18cb6d0 '21', 0) at ../inc/
0000002 ADDPOLL(21, 1, {Proc = {procedure (POINTER, TOBJECT)} 0x7fffffffdda0, Self = 0x1b252a8}, false) at platform/unix/upollthread.pas:67
0000003 TMONITOROBJECT__CREATE(0x1b252a8, 0x1) at platform/unix/linux/uudev.pas:604
0000004 INITIALIZE at platform/unix/linux/uudev.pas:533
0000005 TDRIVEWATCHER__INITIALIZE(0x10dc568, 21477072) at platform/udrivewatcher.pas:241
0000006 TFRMMAIN__FORMCREATE(0x1a09828, 0x1a09828) at fmain.pas:1043
0000007 TCUSTOMFORM__DOCREATE(0x1a09828) at include/
0000008 TCUSTOMFORM__AFTERCONSTRUCTION(0x1a09828) at include/
0000009 TFRMMAIN__AFTERCONSTRUCTION(0x1a09828) at fmain.pas:2646
0000010 TFRMMAIN__CREATE(0x1a09828, 0xffffffffffffffff, 0x1407518) at fmain.pas:2641
0000011 TAPPLICATION__CREATEFORM(0x1407518, 0xe6ed10, ) at include/
0000012 main at doublecmd.lpr:195


#0 fpc_ansistr_setlength(0x0, 281474976710666, 65001) at ../inc/
// local variables of fpc_ansistr_setlength


//#0 fpc_ansistr_concat(0x0, 0xdd92c0 'AddPoll ', 0x18cb6d0 '21', 0) at ../inc/
// local variables
S1='AddPoll '


procedure Print(const sMessage: String);
  WriteLn('PollThread: ', sMessage);

procedure AddPoll(fd: cint; events: cshort; handler: TNotifyEvent;
//0000001 ADDPOLL(21, 1, {Proc = {procedure (POINTER, TOBJECT)} 0x7fffffffdda0, Self = 0x1b252a8}, false) at platform/unix/upollthread.pas:67
  CloseOnDestroy: Boolean);
  AString : String;
    if not Assigned(PollThread) then begin
      PollThread:= TPollThread.Create;
    PollThread.AddPoll(fd, events, handler, CloseOnDestroy);
    AString := IntToStr(fd);
    Print('AddPoll ' + AString);

constructor TMonitorObject.Create;
//0000002 TMONITOROBJECT__CREATE(0x1b252a8, 0x1) at platform/unix/linux/uudev.pas:604
  fd: cint;
  // Get the file descriptor (fd) for the monitor
  // This fd will get passed to poll()
  fd := udev_monitor_get_fd(udev_monitor);

  AddPoll(fd, POLLIN, Handler, False);

  Print('Begin monitoring');

TagsNo tags attached.
Fixed in Revision
Attached Files



2019-05-27 13:13

reporter   ~0116431

Last edited: 2019-05-27 13:14

View 2 revisions

May be related to this bug report :

I'm using Sergei Gorelkin's patch from that bug report.

EDIT : Host and target OS is x86_64-linux.


2019-05-27 13:43

reporter   ~0116432

Last edited: 2019-05-27 13:44

View 2 revisions

Looks like that disabling subroutine inlining for system unit helped. No more SIGSEGV exceptions.

EDIT : I was wrong, it didn't help. :-(


2019-07-23 03:41

reporter   ~0117344

I think that calling System.Str to convert integer to string somehow corrupts stack. There is a thread at the forum about this but I can't remember a link to it.

#0 fpc_ansistr_setlength(0x0, 281474976710666, 65001) at ../inc/
0000001 fpc_ansistr_concat(0x0, 0xdd7a28 'AddPoll ', 0x1851ec0 '26', 0) at ../inc/
0000002 ADDPOLL(26, 1, {Proc = {procedure (POINTER, TOBJECT)} 0x7fffffffdd20, Self = 0x1bfb8c8}, false) at platform/unix/upollthread.pas:64
0000003 TMONITOROBJECT__CREATE(0x1bfb8c8, 0x1) at platform/unix/linux/uudev.pas:604
0000004 INITIALIZE at platform/unix/linux/uudev.pas:533
0000005 TDRIVEWATCHER__INITIALIZE(0x1102400, 27716328) at platform/udrivewatcher.pas:241
0000006 TFRMMAIN__FORMCREATE(0x1978248, 0x1978248) at fmain.pas:1095
0000007 TCUSTOMFORM__DOCREATE(0x1978248) at include/
0000008 TCUSTOMFORM__AFTERCONSTRUCTION(0x1978248) at include/
0000009 TFRMMAIN__AFTERCONSTRUCTION(0x1978248) at fmain.pas:2732
0000010 TFRMMAIN__CREATE(0x1978248, 0xffffffffffffffff, 0x144c9f8) at fmain.pas:2727
0000011 TAPPLICATION__CREATEFORM(0x144c9f8, 0xe48188, ) at include/
0000012 main at doublecmd.lpr:196


2019-07-23 03:50

reporter   ~0117345

platform/unix/upollthread.pas:64          Print('AddPoll ' + IntToStr(fd));
0000000000AFEB4D 488dbd10ffffff           lea    -0xf0(%rbp),%rdi
0000000000AFEB54 e8375e93ff               callq  0x434990 <fpc_ansistr_decr_ref>
0000000000AFEB59 8b75f8                   mov    -0x8(%rbp),%esi
0000000000AFEB5C 488dbd08ffffff           lea    -0xf8(%rbp),%rdi
0000000000AFEB63 e8d8949aff               callq  0x4a8040 <INTTOSTR>
0000000000AFEB68 488b9508ffffff           mov    -0xf8(%rbp),%rdx
0000000000AFEB6F b900000000               mov    $0x0,%ecx
0000000000AFEB74 488d35ad8e2d00           lea    0x2d8ead(%rip),%rsi        # 0xdd7a28 <.Ld2$strlab+24>
0000000000AFEB7B 488dbd10ffffff           lea    -0xf0(%rbp),%rdi
0000000000AFEB82 e8396093ff               callq  0x434bc0 <fpc_ansistr_concat>
0000000000AFEB87 488bbd10ffffff           mov    -0xf0(%rbp),%rdi
0000000000AFEB8E e86dfeffff               callq  0xafea00 <PRINT>
0000000000AFEB93 e8f81d94ff               callq  0x440990 <fpc_popaddrstack>


2019-07-23 06:08

reporter   ~0117346

function IntToStr(Value: Longint): string;
 System.Str(Value, result);
end ;

00000000004A8054 488b5df0                 mov    -0x10(%rbp),%rbx
00000000004A8058 4889df                   mov    %rbx,%rdi
00000000004A805B e830c9f8ff               callq  0x434990 <fpc_ansistr_decr_ref>
00000000004A8060 4889da                   mov    %rbx,%rdx
00000000004A8063 48637df8                 movslq -0x8(%rbp),%rdi
00000000004A8067 b900000000               mov    $0x0,%ecx
00000000004A806C 48c7c6ffffffff           mov    $0xffffffffffffffff,%rsi
00000000004A8073 e808e8f8ff               callq  0x436880 <fpc_ansistr_sint>


2019-07-23 06:10

reporter   ~0117347

Using FPC trunk r42482.


2019-07-26 00:20

reporter   ~0117400

I have found the thread :,45872.msg326710.html#msg326710

Also this bug triggers randomly, either on first execution of program or after several runs.


2019-07-27 07:40

reporter   ~0117428

It seems that cmem unit is the cause for this bug to happen. If I don't use it, there is no SIGSEGV happening after several runs under the GDB debugger or our own debugger (FPdebugger).

Jonas Maebe

2019-07-27 17:40

manager   ~0117437

Last edited: 2019-07-27 17:41

View 2 revisions

Can you try compiling everything with -gv and then run the result under valgrind? (this will also implicitly use cmem)


2019-07-28 09:59

reporter   ~0117451

I compiled everything with -gv (FPC, Lazarus et al) and it is seems to be quite difficult produce this bug at repeated runs under valgrind.

However I managed to get core dump file from gdb when it happened. Here is link to the binary and the core dump plus needed config file so it can be run as stand alone program :


2019-07-28 12:51

reporter   ~0117454

Here is valgrind output. No luck triggering at SIGSEGV error.
valgrind output.7z (157,452 bytes)

Jonas Maebe

2019-07-28 14:08

manager   ~0117457

The IndexByte warnings are false positives. The access(pathname) warning should not cause any issues in either (the syscall will just fail). The Python-related errors look bad though.

jamie philbrook

2019-07-28 16:21

reporter   ~0117461

I've seen random issues like this working with strings, it was due to the fact that using C type string functions there were no #0 (null) character
at the start of an empty string thus leading to the assumption of a huge string when querying the length of it from random garbage in memory.

 using managed string functions on managed strings usually solves this but it isn't the cure. Even managed strings should also have a Null at the end even on empty strings. I use C type string functions on managed strings many times I need to ensure they have a null in them with empty strings.

 Just a thought./

Jonas Maebe

2019-07-28 16:32

manager   ~0117462

> I've seen random issues like this working with strings, it was due to the fact that using C type string functions there were no #0 (null) character
at the start of an empty string

Please provide a test program that demonstrates this problem (in a separate bug report).

Marco van de Voort

2020-07-25 00:24

manager   ~0124316

Hmm, is address 0x7fffffffdda0 (in the addpoll line of the traceback) for a procedure healthy?


2020-11-20 23:20

reporter   ~0127077

I think this bug is caused by inlining. If I disable inlining from both System and SysUtils units, then SIGSEGV doesn't happen.

x86_64-linux target is affected by this. i386-linux works even inlining enabled.


Using now FPC trunk 3.3.1 r47484.


2020-11-24 06:27

reporter   ~0127149

Hmm, disabling inlining didn't help.

#0 fpc_ansistr_setlength(0x0, 281474976710666, 65001) at ../inc/
0000001 fpc_ansistr_concat(0x0, 0xfc92e8 'AddPoll ', 0x1a50ad0 '26', 0) at ../inc/
0000002 ADDPOLL(26, 1, {Proc = {procedure (POINTER, TOBJECT)} 0x7fffffffdbe0, Self = 0x1ee9b48}, false) at platform/unix/upollthread.pas:69
0000003 TMONITOROBJECT__CREATE(0x1ee9b48, 0x1) at platform/unix/linux/uudev.pas:609
0000004 INITIALIZE at platform/unix/linux/uudev.pas:535
0000005 TDRIVEWATCHER__INITIALIZE(0x132a5d8, 24134832) at platform/udrivewatcher.pas:292
0000006 TFRMMAIN__FORMCREATE(0x1bce868, 0x1bce868) at fmain.pas:1132
0000007 TCUSTOMFORM__DOCREATE(0x1bce868) at include/
0000008 TCUSTOMFORM__AFTERCONSTRUCTION(0x1bce868) at include/
0000009 TFRMMAIN__AFTERCONSTRUCTION(0x1bce868) at fmain.pas:2793
0000010 TFRMMAIN__CREATE(0x1bce868, 0xffffffffffffffff, 0x1694f78) at fmain.pas:2788
0000011 TAPPLICATION__CREATEFORM(0x1694f78, 0x10764d0, ) at include/
0000012 main at doublecmd.lpr:204

platform/unix/upollthread.pas:69          Print('AddPoll ' + IntToStr(fd));
0000000000CAA2EE 488dbd10ffffff           lea    -0xf0(%rbp),%rdi
0000000000CAA2F5 e8367578ff               call   0x431830 <fpc_ansistr_decr_ref>
0000000000CAA2FA 8b75f8                   mov    -0x8(%rbp),%esi
0000000000CAA2FD 488dbd08ffffff           lea    -0xf8(%rbp),%rdi
0000000000CAA304 e8176d86ff               call   0x511020 <INTTOSTR>
0000000000CAA309 488b9508ffffff           mov    -0xf8(%rbp),%rdx
0000000000CAA310 b900000000               mov    $0x0,%ecx
0000000000CAA315 488d35ccef3100           lea    0x31efcc(%rip),%rsi        # 0xfc92e8 <.Ld2$strlab+24>
0000000000CAA31C 488dbd10ffffff           lea    -0xf0(%rbp),%rdi
0000000000CAA323 e8787778ff               call   0x431aa0 <fpc_ansistr_concat>
0000000000CAA328 488bbd10ffffff           mov    -0xf0(%rbp),%rdi
0000000000CAA32F e8fcfdffff               call   0xcaa130 <PRINT>
0000000000CAA334 e8e75479ff               call   0x43f820 <fpc_popaddrstack>

Issue History

Date Modified Username Field Change
2019-05-27 13:11 Cyrax New Issue
2019-05-27 13:13 Cyrax Note Added: 0116431
2019-05-27 13:14 Cyrax Note Edited: 0116431 View Revisions
2019-05-27 13:43 Cyrax Note Added: 0116432
2019-05-27 13:44 Cyrax Note Edited: 0116432 View Revisions
2019-07-23 03:41 Cyrax Note Added: 0117344
2019-07-23 03:50 Cyrax Note Added: 0117345
2019-07-23 06:08 Cyrax Note Added: 0117346
2019-07-23 06:10 Cyrax Note Added: 0117347
2019-07-26 00:20 Cyrax Note Added: 0117400
2019-07-27 07:40 Cyrax Note Added: 0117428
2019-07-27 17:40 Jonas Maebe Note Added: 0117437
2019-07-27 17:41 Jonas Maebe Note Edited: 0117437 View Revisions
2019-07-28 09:59 Cyrax Note Added: 0117451
2019-07-28 12:51 Cyrax File Added: valgrind output.7z
2019-07-28 12:51 Cyrax Note Added: 0117454
2019-07-28 14:08 Jonas Maebe Note Added: 0117457
2019-07-28 16:21 jamie philbrook Note Added: 0117461
2019-07-28 16:32 Jonas Maebe Note Added: 0117462
2020-07-25 00:24 Marco van de Voort Note Added: 0124316
2020-11-20 23:20 Cyrax Note Added: 0127077
2020-11-24 06:27 Cyrax Note Added: 0127149