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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 <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson  <rth@twiddle.net>
Message-id: 1466442425-11885-1-git-send-email-peter.maydell@linaro.org
This commit is contained in:
Peter Maydell 2016-06-20 18:07:05 +01:00
parent 7dd929dfdc
commit d7f3040357
1 changed files with 37 additions and 2 deletions
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39
cputlb.c
View File

@ -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);