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 <peter.mayd...@linaro.org> 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 <peter.mayd...@linaro.org> >> --- >> 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 > >