Date: Fri, 21 Nov 1997 16:01:06 -0500 (EST) From: "John S. Dyson" <toor@dyson.iquest.net> To: cbray@best.com Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: malloc() problems in children after using rfork() Message-ID: <199711212101.QAA01392@dyson.iquest.net> In-Reply-To: <3475E143.EE7AF250@best.com> from Curtis Bray at "Nov 21, 97 11:30:12 am"
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Curtis Bray said: > Hi, > > I'm trying to use rfork(RFPROC | RFMEM) so that all the children can > share the same address space with their parent. > > If I have multiple children issuing mallocs the children seem to core > dump. Once I turn the RFMEM flag off I have no problem mallocing (but > of course I loose the shared address space). Anyone know what I could > be doing wrong here? Do I have to put semaphores around every malloc?? > I hope that's not the case... Thanks in advance! > Aieee... rfork is very tricky to use. Take a look at the assembly code that I have included. Note the management of the stack. -- John dyson@freebsd.org jdyson@nc.com .file "rf.S" #include <sys/syscall.h> #include "DEFS.h" #include "SYS.h" #define KERNEL #include <sys/errno.h> #undef KERNEL #undef DEBUG /* * 8 12 16 20 24 28 * _rfork(flags, stack, startrtn, startarg, userrtn, arg); * * flags: RF* flags for rfork in unistd.h. * subr: subroutine to run as a thread. * stack: top of stack for thread. * arg: argument to thread. */ .stabs "rf.S",100,0,0,Ltext0 .text Ltext0: .type _thrfork,@function .stabd 68,0,1 ENTRY(thrfork) pushl %ebp movl %esp, %ebp pushl %esi /* * Push thread info onto the new thread's stack */ movl 12(%ebp), %esi / get stack addr subl $4, %esi movl 28(%ebp), %eax / get user argument movl %eax, (%esi) subl $4, %esi movl 24(%ebp), %eax / get user thread address movl %eax, (%esi) subl $4, %esi movl 20(%ebp), %eax / get internal argument movl %eax, (%esi) subl $4, %esi movl 16(%ebp), %eax / get internal subroutine movl %eax, (%esi) .stabd 68,0,2 /* * Prepare and execute rfork */ pushl 8(%ebp) pushl %esi leal SYS_rfork, %eax KERNCALL jb 2f .stabd 68,0,3 /* * Check to see if we are in the parent or child */ cmpl $0, %edx jnz 1f addl $8, %esp popl %esi movl %ebp, %esp popl %ebp ret .p2align 2 /* * If we are in the child (new thread), then * set-up the call to the internal subroutine. If it * returns, then call __exit. */ .stabd 68,0,4 1: movl %esi,%esp #ifdef DEBUG movl %esp, _stackaddr movl (%esp), %eax movl %eax, _stack movl 4(%esp), %eax movl %eax,_stack+4 movl 8(%esp), %eax movl %eax,_stack+8 movl 12(%esp), %eax movl %eax,_stack+12 #endif popl %eax #ifdef DEBUG movl %eax,_fcn #endif call %eax addl $12, %esp /* * Exit system call */ pushl %eax pushl $SYS_exit call _syscall .stabd 68,0,5 2: movl $EAGAIN, _errno movl $-1, %eax leave ret .stabs "thrfork:f67",36,0,6,_thrfork Lfe1: .size _thrfork,Lfe1-_thrfork #ifdef DEBUG .data .globl _stack _stack: .long 0 .long 0 .long 0 .long 0 .long 0 .globl _stackaddr _stackaddr: .long 0 .globl _fcn _fcn: .long 0 #endif
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