Subject: Re: Cygwin libs broken by "-fomit-frame-pointer" switch
From: [email-masked]
To: <[email-masked]>
Cc: <[email-masked]>
Date: Mon, 30 Apr 2001 18:00:54 -0500

Hi, Rob.

Does the prohibition against "-fomit-frame-pointer" apply to all binaries
build for the Cygwin environment, or is it just a problem for cygwin1.dll?

Thanks for the response.

[email-masked] on 04/30/2001 03:52:34 PM
To:	[email-masked]@SMTP
Steve Snyder/SVL/SC/PHILIPS@AMEC
cc:	 
Subject:	Re: Cygwin libs broken by "-fomit-frame-pointer" switch
Classification:	

IIRC you are breaking fork. We have to work around win32's brokenness.

Rob

---- Original Message -----
From: <[email-masked]>
To: <[email-masked]>
Sent: Tuesday, May 01, 2001 8:47 AM
Subject: Cygwin libs broken by "-fomit-frame-pointer" switch

Hello.

I have noticed that building the Cygwin libraries with the
"-fomit-frame-pointer" compiler switch breaks the libraries.  No errors
are seen in compiling/linking, but an attempt to use a program that
relies
on the library (bash, for instance) always causes a stack fault.  This
is
with v1.3.1-1 of the Cygwin code and v2.95.3-4 of the compiler.

(Some background for those who don't know what I'm talking about: By
default GCC dedicates one of the precious few x86 registers, EBP, as a
base pointer for local variables.  However the stack pointer, ESP, can
just as easily be used for this task, freeing EBP for other uses.  The
"-fomit-frame-pointer" switch tells the compiler to do just that.)

The error always looks similar.  Here is an attempt to use sh.exe:

  handle_exceptions: Exception: STATUS_ACCESS_VIOLATION
  stackdump: Dumping stack trace to sh.exe.stackdump
  sync_with_child: child 151(0x6C) died before initialization with
status code 0xC0000005
  sync_with_child: *** child state waiting for longjmp

Then the dump itself:

  Exception: STATUS_ACCESS_VIOLATION at eip=610245E3
  eax=00000001 ebx=FFFFFFFF ecx=6108E74C edx=02A50000 esi=0A011304
edi=00000000
  ebp=0241F614 esp=0241F8BC program=C:\unix\bin\sh.exe
  cs=001B ds=0023 es=0023 fs=003B gs=0000 ss=0023
  Stack trace:
  Frame     Function  Args
  0241F614  610245E3  (00000000, 00000000, 00000000, 00000000)
  0241FA34  610245E3  (00000000, 0241FA34, 77F6CD00, 0241FD9C)
  02420000  02423348  (EEFFEEFF, 00000002, 00000000, 0000FE00)
    31464 [main] sh 294 handle_exceptions: Exception:
STATUS_ACCESS_VIOLATION
    32081 [main] sh 294 handle_exceptions: Error while dumping state
(probably corrupted stack)

Does the Cygwin Unix-on-Win32 code depend on a frame pointer distinct
from
the stack pointer, or is this a bug?

Thanks.

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