From d7f30403576f04f1f3a5fb5a1d18cba8dfa7a6d2 Mon Sep 17 00:00:00 2001 From: Peter Maydell Date: Mon, 20 Jun 2016 18:07:05 +0100 Subject: [PATCH] cputlb: don't cpu_abort() if guest tries to execute outside RAM or RAM 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 Reviewed-by: Richard Henderson Message-id: 1466442425-11885-1-git-send-email-peter.maydell@linaro.org --- cputlb.c | 39 +++++++++++++++++++++++++++++++++++++-- 1 file changed, 37 insertions(+), 2 deletions(-) diff --git a/cputlb.c b/cputlb.c index 23c9b91200..079e4979ca 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);