Date: Thu, 14 Feb 2008 19:38:50 +0200 From: Kostik Belousov <kostikbel@gmail.com> To: Ruslan Ermilov <ru@freebsd.org> Cc: current@freebsd.org Subject: Re: [src] cvs commit: src/include unistd.h src/lib/libc/sys readlink.2 src/sys/compat/freebsd32 syscalls.master src/sys/kern syscalls.master vfs_syscalls.c src/sys/sys syscallsubr.h Message-ID: <20080214173850.GB57756@deviant.kiev.zoral.com.ua> In-Reply-To: <20080213113530.GB45243@team.vega.ru> References: <200802122009.m1CK94Y8026959@repoman.freebsd.org> <20080212200911.B49F416A51C@hub.freebsd.org> <20080212204803.GT57756@deviant.kiev.zoral.com.ua> <20080213113530.GB45243@team.vega.ru>
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On Wed, Feb 13, 2008 at 02:35:30PM +0300, Ruslan Ermilov wrote:
> [ Replying to the list. ]
>
> On Tue, Feb 12, 2008 at 10:48:04PM +0200, Kostik Belousov wrote:
> > > -int readlink(const char *, char *, int);
> > > +ssize_t readlink(const char *, char *, size_t);
> > You do understand that this changes the ABI ? size_t and int have different
> > sizes on 64-bit arches, and now upper-half of the register used to pass
> > the third arg is used. Amd64, fortunately, makes very hard to load a
> > non-zero into the upper half, I am not so sure about IA64/sparc64.
>
> I considered that. I've tested locally on amd64 and sparc64, and
> ia64 on pluto2.freebsd.org. Since this is only a third argument,
> it's passed in a 64-bit register, and for any meaningful value of it
> (0 .. INT_MAX), there's no ABI change at all. I compared .s files.
>
> : // cc -S a.c ; mv a.s a.s~ ; cc -S -DNEW a.c ; diff -u a.s~ a.s
> : #include <sys/types.h>
> : #include <sys/limits.h>
> :
> : #ifdef NEW
> : ssize_t readlink(const char *, char *, size_t);
> : #else
> : int readlink(const char *, char *, int);
> : #endif
> :
> : void
> : foo(void)
> : {
> : int i;
> : char buf[1024];
> :
> : i = readlink("foo", buf, INT_MAX);
> : }
>
> > This change, IMHO, requires symbol version compat shims.
>
> I don't think so.
>
The slightly contrived example below works on RELENG_7 amd64, relevant
output from the truss is
readlink("/usr/X11R6","l",1) = 1 (0x1)
on the CURRENT gives
readlink("/usr/X11R6","l",1) = -4294967295 (0xffffffff00000001)
[also please note wrong output for the third readlink arg; ktrace/kdump works
ok].
.text
.globl main
main: movq $0xffffffff00000001, %rax
movq %rax, %rdx
movq $buf, %rax
movq %rax, %rsi
movq $path, %rax
movq %rax, %rdi
call readlink
xorl %edi, %edi
call exit
.section .rodata
path: .asciz "/usr/X11R6"
.data
.comm buf, 0x80
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