From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35004) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bHx96-0002nt-Ln for qemu-devel@nongnu.org; Tue, 28 Jun 2016 13:50:01 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bHx94-0006qO-GM for qemu-devel@nongnu.org; Tue, 28 Jun 2016 13:49:59 -0400 Received: from mail-wm0-x22c.google.com ([2a00:1450:400c:c09::22c]:36266) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bHx94-0006qI-62 for qemu-devel@nongnu.org; Tue, 28 Jun 2016 13:49:58 -0400 Received: by mail-wm0-x22c.google.com with SMTP id f126so150090700wma.1 for ; Tue, 28 Jun 2016 10:49:58 -0700 (PDT) Sender: Paolo Bonzini References: <1466442425-11885-1-git-send-email-peter.maydell@linaro.org> From: Paolo Bonzini Message-ID: Date: Tue, 28 Jun 2016 19:49:53 +0200 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] cputlb: don't cpu_abort() if guest tries to execute outside RAM or RAM List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Maydell , QEMU Developers Cc: Patch Tracking , Richard Henderson On 28/06/2016 17:42, Peter Maydell wrote: > Ping for review? The patch is trivial, the hard part was coming up with the message for the user. :) Go ahead! Paolo > thanks > -- PMM > > On 20 June 2016 at 18:07, Peter Maydell wrote: >> In get_page_addr_code(), if the guest program counter turns out not to >> be in ROM or RAM, we can't handle executing from it, and we call >> cpu_abort(). This results in the message >> qemu: fatal: Trying to execute code outside RAM or ROM at 0x08000000 >> followed by a guest register dump, and then QEMU dumps core. >> >> This situation happens in one of two cases: >> (1) a guest kernel bug, where it jumped off into nowhere >> (2) a user command line mistake, where they tried to run an image for >> board A on a QEMU model of board B, or where they didn't provide >> an image at all, and QEMU executed through a ROM or RAM full of >> NOP instructions and then fell off the end >> >> In either case, a core dump of QEMU itself is entirely useless, and >> only confuses users into thinking that this is a bug in QEMU rather >> than a bug in the guest or a problem with their command line. (This >> is a variation on the general idea that we shouldn't assert() on >> something the user can accidentally provoke.) >> >> Replace the cpu_abort() with something that explains the situation >> a bit better and exits QEMU without dumping core. >> >> (See LP:1062220 for several examples of confused users.) >> >> Signed-off-by: Peter Maydell >> --- >> I've been meaning to do this for a while now...hopefully the >> expanded error message should reduce user confusion. >> >> cputlb.c | 39 +++++++++++++++++++++++++++++++++++++-- >> 1 file changed, 37 insertions(+), 2 deletions(-) >> >> diff --git a/cputlb.c b/cputlb.c >> index 23c9b91..079e497 100644 >> --- a/cputlb.c >> +++ b/cputlb.c >> @@ -30,6 +30,8 @@ >> #include "exec/ram_addr.h" >> #include "exec/exec-all.h" >> #include "tcg/tcg.h" >> +#include "qemu/error-report.h" >> +#include "exec/log.h" >> >> /* DEBUG defines, enable DEBUG_TLB_LOG to log to the CPU_LOG_MMU target */ >> /* #define DEBUG_TLB */ >> @@ -427,6 +429,39 @@ void tlb_set_page(CPUState *cpu, target_ulong vaddr, >> prot, mmu_idx, size); >> } >> >> +static void report_bad_exec(CPUState *cpu, target_ulong addr) >> +{ >> + /* Accidentally executing outside RAM or ROM is quite common for >> + * several user-error situations, so report it in a way that >> + * makes it clear that this isn't a QEMU bug and provide suggestions >> + * about what a user could do to fix things. >> + */ >> + error_report("Trying to execute code outside RAM or ROM at 0x" >> + TARGET_FMT_lx, addr); >> + error_printf("This usually means one of the following happened:\n\n" >> + "(1) You told QEMU to execute a kernel for the wrong machine " >> + "type, and it crashed on startup (eg trying to run a " >> + "raspberry pi kernel on a versatilepb QEMU machine)\n" >> + "(2) You didn't give QEMU a kernel or BIOS filename at all, " >> + "and QEMU executed a ROM full of no-op instructions until " >> + "it fell off the end\n" >> + "(3) Your guest kernel has a bug and crashed by jumping " >> + "off into nowhere\n\n" >> + "This is almost always one of the first two, so check your " >> + "command line and that you are using the right type of kernel " >> + "for this machine.\n" >> + "If you think option (3) is likely then you can try debugging " >> + "your guest with the -d debug options; in particular " >> + "-d guest_errors will cause the log to include a dump of the " >> + "guest register state at this point.\n\n" >> + "Execution cannot continue; stopping here.\n\n"); >> + >> + /* Report also to the logs, with more detail including register dump */ >> + qemu_log_mask(LOG_GUEST_ERROR, "qemu: fatal: Trying to execute code " >> + "outside RAM or ROM at 0x" TARGET_FMT_lx "\n", addr); >> + log_cpu_state_mask(LOG_GUEST_ERROR, cpu, CPU_DUMP_FPU | CPU_DUMP_CCOP); >> +} >> + >> /* NOTE: this function can trigger an exception */ >> /* NOTE2: the returned address is not exactly the physical address: it >> * is actually a ram_addr_t (in system mode; the user mode emulation >> @@ -455,8 +490,8 @@ tb_page_addr_t get_page_addr_code(CPUArchState *env1, target_ulong addr) >> if (cc->do_unassigned_access) { >> cc->do_unassigned_access(cpu, addr, false, true, 0, 4); >> } else { >> - cpu_abort(cpu, "Trying to execute code outside RAM or ROM at 0x" >> - TARGET_FMT_lx "\n", addr); >> + report_bad_exec(cpu, addr); >> + exit(1); >> } >> } >> p = (void *)((uintptr_t)addr + env1->tlb_table[mmu_idx][page_index].addend); >> -- >> 1.9.1 > >