Subject: SRR1 bits in signal trampolines
To: None <firstname.lastname@example.org>
From: Aymeric Vincent <email@example.com>
Date: 04/14/2004 13:01:27
when I run "startx", the X server immediately dies as soon as it gets a
SIGALRM, which is as soon as it gets started.
248 XFree86 PSIG SIGALRM caught handler=0x18ae57c mask=())
248 XFree86 CALL compat_16___sigreturn14(0xffffe7e0)
248 XFree86 RET compat_16___sigreturn14 -1 errno 22 Invalid
248 XFree86 CALL exit(0x16)
The problem is with the following test in
if ((sc.sc_frame.srr1 & PSL_USERSTATIC) != (tf->srr1 &PSL_USERSTATIC))
and/or with this definition in powerpc/include/psl.h:
* A user is not allowed to change any MSR bits except the following:
SRR1 can have bits 1-4 and 10-15 modified depending on the exception
taken. In my case, a printf() shows that bit 2 (0x40000000) gets set in
sc.sc_frame.srr1. I don't know why it does now and why it didn't
before, but the fact is that it does, and the documentation says we
shouldn't assume it doesn't.
I think the test in compat_16_sys___sigreturn14() should change to be
less tight (SRR1 is not the MSR), but I am completely unaware of the
consequences of doing so. Could someone knowing the PowerPC better than
me please give a look at this?