Date: Fri, 24 Mar 1995 10:25:23 +0000 From: Ed Hudson <elh@p5.spnet.com> To: hackers@FreeBSD.org Cc: elh@p5.spnet.com Subject: Re: is this reasonable (malloc/sbrk/malloc)? Message-ID: <199503241025.KAA22093@p5.spnet.com> In-Reply-To: Your message of "Fri, 24 Mar 1995 09:37:25 MST." <9503241637.AA09409@cs.weber.edu>
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> >Mixed use of sbrk and malloc is specificially disallowed, even on >SunOs 4.1.3: > >] WARNINGS >] Programs combining the brk() and sbrk() system calls and >] malloc() will not work. Many library routines use malloc() >] internally, so use brk() and sbrk() only when you know that >] malloc() definitely will not be used by any library routine. > > > Terry Lambert > terry@cs.weber.edu howdy. thanks much for the illucidation. but am i mistaken, or is the 'WARNINGS' above abscent in the man pages for fbsd? i ran into this problem porting a large software piece (ocean from olt.et.tudelft.nl), which had some C++ code calling sbrk, and other routines malloc-ing. i've always believed that intermixing was incorrect, but coudn't see any current restrictions stated in fbsd, and had wondered if this might be one of the 4.4 improvements... and even though intermixing may be incorrect, the port under SunOS works correctly (at least for the included test cases). in fbsd, however, subsequent library calls (getcwd() via opendir), check to make sure the space returned by malloc is aligned, and return NULL (with a misleading errno set) if it isn't. i've modified the code i'm porting to make references to malloc instead of sbrk, but i have some concerns that there could be other code that has similar problems (NOT NECESSARILY INTERMIXING malloc and sbrk, but just expecting SBRK to always have aligned behaviour, which fbsd doesn't). certainly the semantics of sbrk() are different in fbsd vs sunos. thanks for the information, but i still question: 1) should fbsd's sbrk returned aligned values, ie, emulate SunOS 4.1.x behavior 2) where's the sbrk/malloc warning in fbsd? confused and still a little concerned... -elh
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