On Fri, Feb 15, 2008 at 12:17:47AM +0300, Ruslan Ermilov wrote: > On Thu, Feb 14, 2008 at 07:38:50PM +0200, Kostik Belousov wrote: > > 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 > > This is because uio_resid is still "int". > > : int > : kern_readlink(struct thread *td, char *path, enum uio_seg pathseg, char *buf, > : enum uio_seg bufseg, size_t count) > [...] > : auio.uio_resid = count; > [...] > : td->td_retval[0] = count - auio.uio_resid; > > uio_resid gets the (truncated) value of "1", VOP_READLINK() > reads 1 char, td_retval[0] gets the value 0xffffffff00000001. > Any meaningful value of the third argument will work OTOH. The point of the conversation I started is exactly this: the domain of the _reasonable_ values for the third arg is changed after your commit. The value that was perfectly acceptable before the commit now causes wrong effects. I consider this to be the ABI change.
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