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Subject: Re: bash::SIGSEGV in timegm () from D:\cygwin64\bin\cygwin1.dll
In-Reply-To: <a78cee42-8e4b-42bb-a1a7-6041a52bcb9f@dronecode.org.uk>
Date: Thu, 22 May 2025 16:44:42 +0100
Cc: cygwin@cygwin.com
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 <a78cee42-8e4b-42bb-a1a7-6041a52bcb9f@dronecode.org.uk>
To: Jon Turney <jon.turney@dronecode.org.uk>
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From: Gary Liddle via Cygwin <cygwin@cygwin.com>
Reply-To: Gary Liddle <gary.liddle@me.com>
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> On 22 May 2025, at 14:30, Jon Turney <jon.turney@dronecode.org.uk> wrote:
> 
> On 22/05/2025 14:15, Gary Liddle via Cygwin wrote:
>> Yesterday I updated Cygwin using  setup-x86_64 to the latest non test release, and bash —login would no longer start.
>> It turns out bash won’t start for me when a .profile runs a sub-command.
>> This is highlighted by:-
>> 	gdb bash
>> 	dll cygwin1.dll
>> 	b timegm
>> 	run
>> 	bash-5.2$ echo foo
>> 	foo
>> 	bash-5.2$ a=`echo foo`
>> 	Program received signal SIGSEGV, Segmentation fault.
>> 	0x00007ffa5cb3ce31 in timegm () from D:\cygwin64\bin\cygwin1.dll
>> 	(gdb)
>> 	...
>> 	bash-5.2$ a=`xxx`
>> 	bash: xxx: command not found
>> 	
>> 	Program received signal SIGSEGV, Segmentation fault.
>> 	0x00007ffa5cb3ce31 in timegm () from D:\cygwin64\bin\cygwin1.dll
>> 	(gdb)
>> 	uname -a CYGWIN_NT-10.0-26100 garyl 3.7.0-0.98.gb39b510c1ce6.x86_64 2025-05-18 15:52 UTC x86_64 Cygwin
> [...]
> 
> Thanks for reporting this.
> 
> 
>> I am at a loss as to how to dig further because gdb doesn’t seem to want to go near timegm and I can’t see anything in the strace output that seems to point to anything useful.
> 
> The information in [1] may be helpful in investigating further with gdb.
> 
> [1] https://cygwin.com/faq.html#faq.programming.debugging-cygwin
> 


Thanks for the link, but all the .dbg programmes segfault in:- 
	ie bash.exe.dbg
	mainCRTStartup () at /usr/src/debug/cygwin-3.4.10-1/winsup/cygwin/crt0.c:16
for all versions (which might be a clue?).

, but the "set cygwin-exceptions on” produces a bit more.

	gdb bash
	Reading symbols from /usr/lib/debug//usr/bin/bash.exe.dbg...
	(gdb) set cygwin-exceptions on
	(gdb) run
	Starting program: /usr/bin/bash
	bash-5.2$ a=`ls`

	Thread 1 "bash" received signal SIGSEGV, Segmentation fault.
	sigdelayed () at sigfe.s:124
	124             movl    %ebx,0x24(%rsp)
	(gdb)
	(gdb) where
	#0  sigdelayed () at sigfe.s:124
	#1  0x000000010042db0b in wait_for (pid=<optimized out>,
	    flags=<error reading variable: Cannot access memory at address 0xfffffffdffffbf08>)
		    at /usr/src/debug/bash-5.2.21-1/jobs.c:3208
	Backtrace stopped: Cannot access memory at address 0xfffffffdffffbef8
…

Which looks very not helpful.

Regards

Gary

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