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

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