Date: Wed, 10 Jul 2002 13:29:34 -0400 (EDT) From: John Baldwin <jhb@FreeBSD.org> To: Serguei Tzukanov <tzukanov@narod.ru> Cc: freebsd-platforms@freebsd.org, freebsd-hackers@freebsd.org Subject: Re: A question about S/390 port Message-ID: <XFMail.20020710132934.jhb@FreeBSD.org> In-Reply-To: <200207102033.25184.tzukanov@narod.ru>
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On 10-Jul-2002 Serguei Tzukanov wrote: > >> td_retval[0] is the low word, and td_retval[1] is the high word, you >> just need to make sure the values from those two words get returned >> properly to userland. > > 1) syscall returns 32-bit value: > r2 = rv[0]; > r3 = rv[1]; > r3 is irrelevant here (ABI: "32-bit values returned in r2") > > 2) syscall returns 64-bit value: > MI code uses something like > *(int64_t *)rv = xxx, so I have to do > r2 = rv[0]; > r3 = rv[1]; > ABI says "long long shall be returned with the lower > addressed half in r2 and the higher in r3" > > 3) syscall folded into __syscall returns 32-bit value (e.g. mmap): > MI code does usual > r[0] = xxx; > svc (syscall) handler does > r2 = rv[0]; > r3 = rv[1]; /* zeroed before */ > then mmap wrapper in userspace casts this 64-bit to 32-bit > (loads r2 with r3 really) and always gets 0. Why does the cast from 32 to 64 treat r3 as the lower 32-bits when a 64-bit return value treats r3 as the upper 32-bits and r2 as the lower 32-bits? That is inconsistent and you are going to have problems with either one or the other. I also don't understand exactly what you mean by "syscall folded into __syscall". -- John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve!" - http://www.FreeBSD.org/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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