[Qemu-devel] [PATCH] armv7m: optional -kernel if -gdb present

[Qemu-devel] [PATCH] armv7m: optional -kernel if -gdb present

[Liviu Ionescu]

For standalone emulation, the image must be specified via -kernel,
but when using QEMU as a GDB server, the presence of -kernel is
no longer mandatory, since the image can be loaded by the GDB client.

Signed-off-by: Liviu Ionescu <ilg@livius.net>
---
 hw/arm/armv7m.c         | 3 ++-
 include/sysemu/sysemu.h | 1 +
 vl.c                    | 7 ++++++-
 3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/hw/arm/armv7m.c b/hw/arm/armv7m.c
index 696de12..9d1669c 100644
--- a/hw/arm/armv7m.c
+++ b/hw/arm/armv7m.c
@@ -14,6 +14,7 @@
 #include "sysemu/qtest.h"
 #include "qemu/error-report.h"
 #include "hw/boards.h"
+#include "sysemu/sysemu.h"
 
 static struct arm_boot_info armv7m_binfo;
 
@@ -241,7 +242,7 @@ qemu_irq *armv7m_init(MemoryRegion *system_memory,
     big_endian = 0;
 #endif
 
-    if (!kernel_filename && !qtest_enabled()) {
+    if (!kernel_filename && !qtest_enabled() && !with_gdb) {
         fprintf(stderr, "Guest image must be specified (using -kernel)\n");
         exit(1);
     }
diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
index c145d94..08bbe71 100644
--- a/include/sysemu/sysemu.h
+++ b/include/sysemu/sysemu.h
@@ -104,6 +104,7 @@ typedef enum DisplayType
 } DisplayType;
 
 extern int autostart;
+extern int with_gdb;
 
 typedef enum {
     VGA_NONE, VGA_STD, VGA_CIRRUS, VGA_VMWARE, VGA_XENFB, VGA_QXL,
diff --git a/vl.c b/vl.c
index a88e5da..4a03fb8 100644
--- a/vl.c
+++ b/vl.c
@@ -138,6 +138,7 @@ bool enable_mlock = false;
 int nb_nics;
 NICInfo nd_table[MAX_NICS];
 int autostart;
+int with_gdb;
 static int rtc_utc = 1;
 static int rtc_date_offset = -1; /* -1 means no change */
 QEMUClockType rtc_clock;
@@ -2797,6 +2798,7 @@ int main(int argc, char **argv, char **envp)
     uint64_t ram_slots = 0;
     FILE *vmstate_dump_file = NULL;
     Error *main_loop_err = NULL;
+    with_gdb = false;
 
     atexit(qemu_run_exit_notifiers);
     error_set_progname(argv[0]);
@@ -3241,9 +3243,11 @@ int main(int argc, char **argv, char **envp)
                 break;
             case QEMU_OPTION_s:
                 add_device_config(DEV_GDB, "tcp::" DEFAULT_GDBSTUB_PORT);
+                with_gdb = true;
                 break;
             case QEMU_OPTION_gdb:
                 add_device_config(DEV_GDB, optarg);
+                with_gdb = true;
                 break;
             case QEMU_OPTION_L:
                 if (data_dir_idx < ARRAY_SIZE(data_dir)) {
@@ -4443,7 +4447,8 @@ int main(int argc, char **argv, char **envp)
             error_free(local_err);
             exit(1);
         }
-    } else if (autostart) {
+    } else if (autostart && kernel_filename) {
+        /* If an image is defined and no -S is requested, start it. */
         vm_start();
     }
 
-- 
1.9.3 (Apple Git-50)

Re: [Qemu-devel] [PATCH] armv7m: optional -kernel if -gdb present

[Peter Maydell]

On 20 November 2014 12:05, Liviu Ionescu <ilg@livius.net> wrote:
> For standalone emulation, the image must be specified via -kernel,
> but when using QEMU as a GDB server, the presence of -kernel is
> no longer mandatory, since the image can be loaded by the GDB client.

I think the correct fix for this issue is:

> -    if (!kernel_filename && !qtest_enabled()) {
> +    if (!kernel_filename && !qtest_enabled() && !with_gdb) {
>          fprintf(stderr, "Guest image must be specified (using -kernel)\n");
>          exit(1);
>      }

just delete this entire if() statement. This is how we've handled
similar issues with the ARM A profile boards. (Some of the boards
still have those checks but that's just because nobody's bothered
to fix them yet.)

thanks
-- PMM

Re: [Qemu-devel] [PATCH] armv7m: optional -kernel if -gdb present

[Liviu Ionescu]

On 20 Nov 2014, at 14:29, Peter Maydell <peter.maydell@linaro.org> wrote:

>> -    if (!kernel_filename && !qtest_enabled()) {
>> +    if (!kernel_filename && !qtest_enabled() && !with_gdb) {
>>         fprintf(stderr, "Guest image must be specified (using -kernel)\n");
>>         exit(1);
>>     }
> 
> just delete this entire if() statement. This is how we've handled
> similar issues with the ARM A profile boards. (Some of the boards
> still have those checks but that's just because nobody's bothered
> to fix them yet.)

I'm a bit confused. if not running with gdb, what is the expected behaviour if the image is missing?


Liviu

Re: [Qemu-devel] [PATCH] armv7m: optional -kernel if -gdb present

[Peter Maydell]

On 20 November 2014 12:34, Liviu Ionescu <ilg@livius.net> wrote:
>
> On 20 Nov 2014, at 14:29, Peter Maydell <peter.maydell@linaro.org> wrote:
>
>>> -    if (!kernel_filename && !qtest_enabled()) {
>>> +    if (!kernel_filename && !qtest_enabled() && !with_gdb) {
>>>         fprintf(stderr, "Guest image must be specified (using -kernel)\n");
>>>         exit(1);
>>>     }
>>
>> just delete this entire if() statement. This is how we've handled
>> similar issues with the ARM A profile boards. (Some of the boards
>> still have those checks but that's just because nobody's bothered
>> to fix them yet.)
>
> I'm a bit confused. if not running with gdb, what is the expected
> behaviour if the image is missing?

Same thing as if you start a hardware board with nothing loaded
into the flash. (Probably this means "go into an infinite loop
of taking exceptions".)

-- PMM

Re: [Qemu-devel] [PATCH] armv7m: optional -kernel if -gdb present

[Liviu Ionescu]

On 20 Nov 2014, at 14:50, Peter Maydell <peter.maydell@linaro.org> wrote:

> Same thing as if you start a hardware board with nothing loaded
> into the flash. (Probably this means "go into an infinite loop
> of taking exceptions".)

hmmm... and you consider this behaviour to meet the user-friendly requirements?

I tried it, and the program simply hangs, without any stdout/stderr messages.

if you find this behaviour acceptable for unix users, ok, you don't have to update the other profiles, but for most cortex-m users it is confusing, and user-friendliness is not only appreciated, but required.

I would appreciate you reconsider the patch.

thank you,

Liviu

Re: [Qemu-devel] [PATCH] armv7m: optional -kernel if -gdb present

[Peter Maydell]

On 20 November 2014 13:09, Liviu Ionescu <ilg@livius.net> wrote:
>
> On 20 Nov 2014, at 14:50, Peter Maydell <peter.maydell@linaro.org> wrote:
>
>> Same thing as if you start a hardware board with nothing loaded
>> into the flash. (Probably this means "go into an infinite loop
>> of taking exceptions".)
>
> hmmm... and you consider this behaviour to meet the user-friendly requirements?
>
> I tried it, and the program simply hangs, without any stdout/stderr messages.

Yes. That's what hardware does in that situation.

I don't think that whether or not a debugger has been connected
should change our behaviour. (And even with your patch, if you
connect a debugger and just hit its 'run' button without loading
an image then we'll do the same exception-loop.)

> if you find this behaviour acceptable for unix users, ok, you don't
> have to update the other profiles, but for most cortex-m users it is
> confusing, and user-friendliness is not only appreciated, but required.

I agree it's not very user friendly. But I don't like inconsistency
between our behaviour for different boards either. (And for some
boards we're going to have a bios or other firmware which will
run if you don't specify -kernel.)

In general I think many of the concerns you're raising here
are real problems, and our user-friendliness is indeed poor
in a lot of places. However the solutions you're proposing
are often specific to M-profile ARM, whereas I have to consider
the whole project and would prefer solutions which clean
up and deal with an issue for all boards and all CPUs.
That's obviously harder than a more local and restricted
fix, but the benefit is greater.

thanks
-- PMM

Re: [Qemu-devel] [PATCH] armv7m: optional -kernel if -gdb present

[Liviu Ionescu]

On 20 Nov 2014, at 15:20, Peter Maydell <peter.maydell@linaro.org> wrote:

> ... However the solutions you're proposing
> are often specific to M-profile ARM,

ok, I'll keep this local to my branch.

what about the previous patch, is it acceptable?


regards,

Liviu