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Subject: Re: fork fails after nmap with hint address in an unmapped memory region
To: The Cygwin Mailing List <cygwin AT cygwin DOT com>
References: <b431898c-30f5-2847-c922-0f25a525ef76 AT yahoo DOT fr> <15510444518 DOT 20171209184819 AT yandex DOT ru> <42c71a45-e61b-6917-b634-e912fb51d2d5 AT yahoo DOT fr> <56047a39-4e1e-fa50-0e8b-c123c5b5ed3c AT SystematicSw DOT ab DOT ca>
From: Jon Turney <jon DOT turney AT dronecode DOT org DOT uk>
Cc: Brian DOT Inglis AT SystematicSw DOT ab DOT ca
Message-ID: <cd9b5838-2545-362e-6e02-a46749791d6f@dronecode.org.uk>
Date: Sat, 9 Dec 2017 22:51:47 +0000
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On 09/12/2017 18:29, Brian Inglis wrote:
> On 2017-12-09 08:53, Stéphane Mbape via cygwin wrote:
>> Le 09/12/2017 à 16:48, Andrey Repin a écrit :
>>>> While embeding luajit in a c  program, I found myself unable to fork
>>>> processes.
>>>> Investigations prove that it was related to nmap.
>>>> To be accurate, calling nmap with hint address in a unmapped memory
>>>> region will cause all forks to fail with
>>>> "fixup_mmaps_after_fork: ReadProcessMemory failed for MAP_PRIVATE
>>>> address 0x6FFFFFE0000, Win32 error 299"
>>>> There is a sample code below.
>>> You forgot to mention Cygwin version you're using, and please provide the
>>> sample as an attach to save people the copy-pasting issues.
>> Cygwin version: 2.9.0
>> OS: Windows 10
>> Arch: 64bit
>> The sample was also attached.
> 
> Confirmed reproducible; addr2line does not give anything useful from the
> stackdump, but included raw stackdump below, in case it gives hints.

If you're going to use addr2line to interpret a .stackdump file, I'm 
afraid you're just supposed to know that the cygwin1.dll has an 
ImageBase of 0x0000000180040000 on x86_64

> $ more mmap_fork_stc.exe.stackdump
> Stack trace:
> Frame        Function    Args
> 000005FF3A0  0018005CD8E (0018021AE80, 0018021AC46, 00000008000, 000005FB010)
> 000005FF3A0  001800465F9 (000005FDDE0, 000005FF3A0, 001800B2D10, 00000000000)
> 000005FF3A0  00180046632 (00000000000, 000005FBE28, 00000008000, 00100402068)
> 000005FF3A0  00180046B84 (0007FFE0385, 000005FDDE0, 001800B2D10, 00000000000)
> 000005FF3A0  00180048040 (00000000000, 00000000000, 00000000000, 00000000000)
> 000005FF3A0  001800B2EDB (00000000000, 00000000000, 00000000000, 00000000000)
> 000005FF620  7FFF7777485F (00180040000, 00000000001, 00000240022, 000006D20C8)
> 000005FF620  7FFF7779D762 (7FFF77797900, 000006D2701, 7FFF774A27BA, 000006D2F10)
> 000005FF620  7FFF7779D5AB (000006D2720, 000005FF5D0, 00000000003, 0000032E000)
> 000005FF620  7FFF7779D5D1 (00000000003, 000005FF629, 00000000003, 00000000000)
> 00000000000  7FFF777E1D31 (00000000000, 00000000000, 00000000001, 00000000000)
> 00000000000  7FFF7781A1FC (00000000000, 00000000000, 0000032E000, 00000000000)
> 00000000000  7FFF777C9B1B (00000000000, 00000000000, 00000000000, 00000000000)
> 00000000000  7FFF777C9ACE (00000000000, 00000000000, 00000000000, 00000000000)
> End of stack trace

Sator Arepo Tenet Opera Rotas! [1]

0x000000018005cd8e    cygwin_stackdump                 exceptions.cc:456
0x00000001800465f9    vapi_fatal                        dcrt0.cc:1296
0x0000000180046632    api_fatal                         dcrt0.cc:1305
0x0000000180046b84    child_info_fork::handle_fork()    dcrt0.cc:634
0x0000000180048040    dll_crt0_0()                      dcrt0.cc:777
0x00000001800b2edb    dll_entry                         init.cc:102

[1] https://cygwin.com/ml/cygwin/2015-08/msg00311.html


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