On Tue, Sep 25, 2001 at 08:51:03PM +0200, tommy.christensen@eicon.com wrote: > For some time, I have seen occasional corruption of tty-output (pty's and > serial). This turned out to be caused by a register collision in read_chan > () > in n_tty.c. In the expansion of copy_to_user, the compiler chose register > "a0" to hold the value of local variable __cu_from. Since this register is > modified in the asm statement, before __cu_from is used, the corruption > occured. > > I am not sure, whether this is a compiler-bug (egcs-2.91.66) or the code > should prevent this from happening. Have the semantics about side-effects > of asm statements changed? > > Anyway, the attached patch solves this by explicitly building the arguments > to __copy_user in the argument registers ;-) instead of moving them around. > So it actually saves some instructions as well. And the compiler can > generate better code since it now has more registers for temporary > variables ... > > Is this OK? It works just fine for me with a 2.4.9 kernel (VR5000). Unfortunately I had to find that your bugreport is correct. To make things worse at the time when I implemented this code I used your approach (which definately is the cleaner approach) and I ran into the same problem. Ralf
