From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:44155) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a4GJN-00066k-DH for qemu-devel@nongnu.org; Wed, 02 Dec 2015 17:55:46 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1a4GJM-0002CO-Ab for qemu-devel@nongnu.org; Wed, 02 Dec 2015 17:55:45 -0500 Message-ID: <565F76E7.4060305@gmail.com> Date: Wed, 02 Dec 2015 17:55:35 -0500 From: Michael Davidsaver MIME-Version: 1.0 References: <1447031505-12477-1-git-send-email-mdavidsaver@gmail.com> <1447031505-12477-5-git-send-email-mdavidsaver@gmail.com> In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 04/18] armv7m: Explicit error for bad vector table List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Maydell Cc: Peter Crosthwaite , qemu-arm@nongnu.org, QEMU Developers On 11/17/2015 12:33 PM, Peter Maydell wrote: > On 9 November 2015 at 01:11, Michael Davidsaver wrote: >> Give an explicit error and abort when a load >> from VECBASE fails. Otherwise would likely >> jump to 0, which for v7-m holds the reset stack >> pointer address. >> >> Signed-off-by: Michael Davidsaver >> --- >> target-arm/helper.c | 12 +++++++++++- >> 1 file changed, 11 insertions(+), 1 deletion(-) >> >> diff --git a/target-arm/helper.c b/target-arm/helper.c >> index 4178400..1d7ac43 100644 >> --- a/target-arm/helper.c >> +++ b/target-arm/helper.c >> @@ -5496,7 +5496,17 @@ void arm_v7m_cpu_do_interrupt(CPUState *cs) >> /* Clear IT bits */ >> env->condexec_bits = 0; >> env->regs[14] = lr; >> - addr = ldl_phys(cs->as, env->v7m.vecbase + env->v7m.exception * 4); >> + { >> + MemTxResult result; >> + addr = address_space_ldl(cs->as, >> + env->v7m.vecbase + env->v7m.exception * 4, >> + MEMTXATTRS_UNSPECIFIED, &result); >> + if (result != MEMTX_OK) { >> + cpu_abort(cs, "Failed to read from exception vector table " >> + "entry %08x\n", >> + env->v7m.vecbase + env->v7m.exception * 4); >> + } >> + } > > The behaviour on a failed vector table read is actually architecturally > specified: we should take a nested exception (escalated to HardFault). > If it happens while we're trying to take a HardFault in the first place > then we go into Lockup (where the CPU sits around repeatedly trying > to execute an instruction at 0xFFFFFFFE; it is technically possible > to get back out of Lockup by taking an NMI or a system reset). > > That said, trying to get nested exceptions and priority escalation > right is fairly involved, and implementing lockup is both involved > and an exercise in pointlessness. So I think this code is an > improvement overall. This is my thinking as well. One point against it is that abort() is inconvenient when using '-gdb'. I'm not sure if there is something else which could be done (cpu halt?). > I would suggest some small changes, though: > > (1) factor this out into its own function, something like: > static uint32_t v7m_read_vector(CPUARMState *env, int excnum) > so the calling code can just do > addr = v7m_read_vector(env, env->v7m.exception); > (2) use a local variable for "env->v7m.vecbase + excnum * 4" > rather than calculating it twice Done.