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console: Fix segfault on screendump without VGA adapter

PATCH New Alexander Graf 4 participants 5 messages Nov 18, 2011 – Nov 22, 2011

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Alexander Graf

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#0 lore raw

PATCH 1/1 console: Fix segfault on screendump without VGA adapter

When trying to create a screen dump without having any VGA adapter inside the guest, QEMU segfaults.

This is because it's trying to switch back to the "previous" screen it was on before dumping the VGA screen. Unfortunately, in my case there simply is no previous screen so it accesses a NULL pointer.

Fix it by checking if previous_active_console is actually available.

This is 1.0 material.

Signed-off-by Alexander Graf <[email protected]>
---
 console.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
console.c +3 -1
index f6fe441..ed6a653 100644
@@ -186,7 +186,9 @@ void vga_hw_screen_dump(const char *filename)
         consoles[0]->hw_screen_dump(consoles[0]->hw, filename);
     }
 
-    console_select(previous_active_console->index);
+    if (previous_active_console) {
+        console_select(previous_active_console->index);
+    }
 }
 
 void vga_hw_text_update(console_ch_t *chardata)
Signature · 1 line
1.6.0.2
#1 lore raw

PATCH 1/1 creen dump not supported when no console

I have tested the issue use "-vga none -nographic" option. QEMU segment faults.

But i think there is no any text and graphic console created in this case. The console[0] is NULL.

The vga_hw_screen_dump() should return before console_select(). What do you think?

---
 console.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
console.c +3 -0
index f6fe441..957948e 100644
@@ -184,6 +184,9 @@ void vga_hw_screen_dump(const char *filename)
     console_select(0);
     if (consoles[0] && consoles[0]->hw_screen_dump) {
         consoles[0]->hw_screen_dump(consoles[0]->hw, filename);
+    } else {
+	fprintf(stderr,"no any console,could not screen dump \n");
+	return;
     }
 
     console_select(previous_active_console->index);
Signature · 1 line
1.7.1
#2 lore raw

Re: [Qemu-devel] [PATCH] creen dump not supported when no console

console.c void vga_hw_screen_dump(const char *filename) · line 189

Quoted 3 lines · Cao,Bing Bu
console.c +3 -0
+    } else {
+	fprintf(stderr,"no any console,could not screen dump \n");
+	return;

This should be error_printf.

Paolo

#3 lore raw

PATCH v2 1/1 Can't screendump without a console

When usinge "-vga none -nographic" option.
There is no any text and graphic console created in this case. screen dump not supported without console.

Signed-off-by Cao,Bing Bu <[email protected]>
---
 console.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
console.c +3 -1
index f6fe441..6071ef3 100644
@@ -184,8 +184,10 @@ void vga_hw_screen_dump(const char *filename)
     console_select(0);
     if (consoles[0] && consoles[0]->hw_screen_dump) {
         consoles[0]->hw_screen_dump(consoles[0]->hw, filename);
+    } else {
+        error_printf("no any console,could not screen dump \n");
+        return;
     }
-
     console_select(previous_active_console->index);
 }
Signature · 1 line
1.7.1
#4 lore raw

Re: [Qemu-devel] [PATCH] creen dump not supported when no console

In reply to Cao,Bing Bu
Quoted 19 lines · Cao,Bing Bu

I have tested the issue use "-vga none -nographic" option. QEMU segment faults.

But i think there is no any text and graphic console created in this case. The console[0] is NULL.

The vga_hw_screen_dump() should return before console_select(). What do you think?

---
 console.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
console.c +0 -0
index f6fe441..957948e 100644

console.c void vga_hw_screen_dump(const char *filename) · line 192

Quoted 9 lines
console.c +3 -0
@@ -184,6 +184,9 @@ void vga_hw_screen_dump(const char *filename)
     console_select(0);
     if (consoles[0] && consoles[0]->hw_screen_dump) {
         consoles[0]->hw_screen_dump(consoles[0]->hw, filename);
+    } else {
+	fprintf(stderr,"no any console,could not screen dump \n");
+	return;
     }
 
     console_select(previous_active_console->index);

Tab damage.

Subject misspells "screendump".

Error message could use some polish. Suggest "Can't screendump without a console".

Please don't use printf & friends for output to the monitor user, it doesn't go to the monitor unless the monitor happens to be on stdio. Use error_printf() & friends.

Except when the command is in QMP, and you need nice error reports in QMP. Then use qerror_report(). Yes, that's a pain to use.

Except when the command is already implemented in QAPI. Then you use error_set() instead. Yes, that one's a PITA, too.