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[Qemu-devel] [PATCH] cputlb: don't cpu_abort() if guest tries to execute
From: |
Peter Maydell |
Subject: |
[Qemu-devel] [PATCH] cputlb: don't cpu_abort() if guest tries to execute outside RAM or RAM |
Date: |
Mon, 20 Jun 2016 18:07:05 +0100 |
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 <address@hidden>
---
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
- [Qemu-devel] [PATCH] cputlb: don't cpu_abort() if guest tries to execute outside RAM or RAM,
Peter Maydell <=