Date: Tue, 24 Sep 2013 00:37:30 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Tijl Coosemans <tijl@coosemans.org> Cc: freebsd-current@FreeBSD.org, Russ Cox <rsc@swtch.com> Subject: Re: restarting SYSCALL system call on amd64 loses arguments Message-ID: <20130923213730.GX41229@kib.kiev.ua> In-Reply-To: <20130923222613.548860a3@kalimero.tijl.coosemans.org> References: <20130923222613.548860a3@kalimero.tijl.coosemans.org>
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--0QZ35bX9xAXmZuwY Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Sep 23, 2013 at 10:26:13PM +0200, Tijl Coosemans wrote: > Has anyone taken a look at this PR yet? >=20 > http://www.freebsd.org/cgi/query-pr.cgi?pr=3D182161 This looks like a valid bug, but probably not a valid testcase. Let me elaborate. When a signal is delivered, return from the signal handler is performed by the sigreturn(2), which reloads the whole register file when crossing kernel->user boundary due to sys_sigreturn(9) setting PCB_FULL_IRET flag. As result, the whole trap frame at the time of the syscall entry is restored, and ERESTART return is not exercised. I was not able to reproduce the issue with the supplied test program on HEAD. I suspect that the program actually exposed the bug in the signal delivery in the threaded processes, which I introduced for 9.1 and fixed in r251047 & r251365. On the other hand, I agree that at least arguments should be restored for ERESTART case, but in fact it is easier and probably less error-prone to restore whole register file again. Please try the patch below for your Go code. diff --git a/sys/amd64/amd64/vm_machdep.c b/sys/amd64/amd64/vm_machdep.c index b7c2b67..1e3d8f5 100644 --- a/sys/amd64/amd64/vm_machdep.c +++ b/sys/amd64/amd64/vm_machdep.c @@ -400,9 +400,13 @@ cpu_set_syscall_retval(struct thread *td, int error) * for the next iteration. * %r10 restore is only required for freebsd/amd64 processes, * but shall be innocent for any ia32 ABI. + * + * Require full context restore to get the arguments + * in the registers reloaded at return to usermode. */ td->td_frame->tf_rip -=3D td->td_frame->tf_err; td->td_frame->tf_r10 =3D td->td_frame->tf_rcx; + set_pcb_flags(td->td_pcb, PCB_FULL_IRET); break; =20 case EJUSTRETURN: --0QZ35bX9xAXmZuwY Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.21 (FreeBSD) iQIcBAEBAgAGBQJSQLSZAAoJEJDCuSvBvK1B+XAP/A/myszBMjClt+E41gilgIjo O9hCqr/7tUZR4ZtIa7QcIdOF9NPJgLYtDJo8dfBSr4ITPBVzNP5v7P6gRej40z/p aCnwPy3rzatJIOfZQtIo/4NAU3N4DFNizqLWt+6eJuSfym1ATKLZfuI5DBmKeKbP 6CV6F2noy7t5hPnCSWUYce9u82FanKJpS/La/ccxttSES5V0MKSPF3hpugGpUoU2 /i/5zVC5MgJ2sLeoYzOtkkI/dwYN5LhUDilg55uSAv4hY++lpdc9mUm2RLYJOV/S /ZwnXW9rym2rRzWXg6/S0cZXXGL2YsUGuRcfLVdLiFdHaxsUzuKGCDSSnAt6MGy8 GFEnal/23I/ULsDSjHfsqDpM95ucOmNj3I7BL6aF8P82Oib4g1rfo7JCTMYouQm5 BV2JDGcQi/lqKrGY1xhjk535SthLpw87tQv/PqiXdRLApc4w0y3ILwvttR5Qe+6k v6zG4t2p24zl8UCGN3yFwfMJOLXRy4bturLGVURd7uPib/M2T2Q5TOei049sXT3d X+QQz/jbTFOE7IASG7JKWU5BI29D4awF8ijFGuU/50RObW/xCfa5YYKleCE37LXL 4YRemRX0ONihAneP3n0XexsZpEMqZ/4E+vfqlvbvghNIq8tFwVaGl2RxyQMk7VU5 DYI7pWV/bF0paiEIWHnN =q7Lk -----END PGP SIGNATURE----- --0QZ35bX9xAXmZuwY--
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