[PATCH] scripts/gdb: fix lx-version for gdb 7.3-

[PATCH] scripts/gdb: fix lx-version for gdb 7.3-

[Du Changbin]

For gdb version less than 7.3, lx-version only one character.
(gdb) lx-version
L(gdb)

This can be fixed by casting 'linux_banner' as (char *).
(gdb) lx-version
Linux version 4.19.0-rc1+ (changbin@acer) (gcc version 7.3.0 (Ubuntu 7.3.0-16ubuntu3)) #21 SMP Sat Sep 1 21:43:30 CST 2018

gdb 7.4 seems to be no such issue.

Signed-off-by: Du Changbin <changbin.du@gmail.com>
---
 scripts/gdb/linux/proc.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/gdb/linux/proc.py b/scripts/gdb/linux/proc.py
index 086d27223c0c..0aebd7565b03 100644
--- a/scripts/gdb/linux/proc.py
+++ b/scripts/gdb/linux/proc.py
@@ -41,7 +41,7 @@ class LxVersion(gdb.Command):
 
     def invoke(self, arg, from_tty):
         # linux_banner should contain a newline
-        gdb.write(gdb.parse_and_eval("linux_banner").string())
+        gdb.write(gdb.parse_and_eval("(char *)linux_banner").string())
 
 LxVersion()
 
-- 
2.17.1

Re: [PATCH] scripts/gdb: fix lx-version for gdb 7.3-

[Jan Kiszka]

On 17.10.18 04:36, Du Changbin wrote:
> For gdb version less than 7.3, lx-version only one character.

                                           ^^^ prints?

> (gdb) lx-version
> L(gdb)
> 
> This can be fixed by casting 'linux_banner' as (char *).
> (gdb) lx-version
> Linux version 4.19.0-rc1+ (changbin@acer) (gcc version 7.3.0 (Ubuntu 7.3.0-16ubuntu3)) #21 SMP Sat Sep 1 21:43:30 CST 2018
> 
> gdb 7.4 seems to be no such issue.
> 
> Signed-off-by: Du Changbin <changbin.du@gmail.com>
> ---
>   scripts/gdb/linux/proc.py | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/scripts/gdb/linux/proc.py b/scripts/gdb/linux/proc.py
> index 086d27223c0c..0aebd7565b03 100644
> --- a/scripts/gdb/linux/proc.py
> +++ b/scripts/gdb/linux/proc.py
> @@ -41,7 +41,7 @@ class LxVersion(gdb.Command):
>   
>       def invoke(self, arg, from_tty):
>           # linux_banner should contain a newline
> -        gdb.write(gdb.parse_and_eval("linux_banner").string())
> +        gdb.write(gdb.parse_and_eval("(char *)linux_banner").string())
>   
>   LxVersion()
>   
> 

Looks good to me otherwise.

Jan

-- 
Siemens AG, Corporate Technology, CT RDA IOT SES-DE
Corporate Competence Center Embedded Linux

Re: [PATCH] scripts/gdb: fix lx-version for gdb 7.3-

[Kieran Bingham]

Hi Du,

On 17/10/18 03:36, Du Changbin wrote:
> For gdb version less than 7.3, lx-version only one character.
> (gdb) lx-version
> L(gdb)
> 
> This can be fixed by casting 'linux_banner' as (char *).
> (gdb) lx-version
> Linux version 4.19.0-rc1+ (changbin@acer) (gcc version 7.3.0 (Ubuntu 7.3.0-16ubuntu3)) #21 SMP Sat Sep 1 21:43:30 CST 2018
> 
> gdb 7.4 seems to be no such issue.
> 
> Signed-off-by: Du Changbin <changbin.du@gmail.com>
> ---
>  scripts/gdb/linux/proc.py | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/scripts/gdb/linux/proc.py b/scripts/gdb/linux/proc.py
> index 086d27223c0c..0aebd7565b03 100644
> --- a/scripts/gdb/linux/proc.py
> +++ b/scripts/gdb/linux/proc.py
> @@ -41,7 +41,7 @@ class LxVersion(gdb.Command):
>  
>      def invoke(self, arg, from_tty):
>          # linux_banner should contain a newline
> -        gdb.write(gdb.parse_and_eval("linux_banner").string())
> +        gdb.write(gdb.parse_and_eval("(char *)linux_banner").string())


Interesting - this is an issue I reported to the GDB team after I'd
tried to dig into the fault.

  https://sourceware.org/bugzilla/show_bug.cgi?id=20077

the parse_and_eval finds a string length of 0, but then later in the GBD
parsing it gets incremented to 1, hence the single char. I guess it's
some failure in GDB determining the type of the pointer.

However, from reading the bugzilla entry and from what I recall - it
only occurred if you had done a backtrace before calling lx-version.

Did you discover that it would always return only the single character
in your testing ? Even if it was the first command executed?

My worry is - that if this fixes lx-version - do we also need to
manually cast lx-cmdline as well ? (I never saw the issue occur on that
cmd).

I think considering the age of the bugzilla at GDB, and the lack of any
GDB level fix or understanding - we should certainly apply this fix here
- and probably include it in the stable trees too.


With the title fix as highlighted by Jan,

Reviewed-by: Kieran Bingham <kbingham@kernel.org>

Would you be able to test the issue with the lx-cmdline command as well
please? And if it is suffering the same issue - perhaps you could either
submit a second patch to update that entry - or respin this one to
include both?



>  
>  LxVersion()
>  
> 


-- 
Regards
--
Kieran

Re: [PATCH] scripts/gdb: fix lx-version for gdb 7.3-

[Changbin Du]

On Wed, Oct 17, 2018 at 08:56:44AM +0200, Jan Kiszka wrote:
> On 17.10.18 04:36, Du Changbin wrote:
> > For gdb version less than 7.3, lx-version only one character.
>
>                                           ^^^ prints?
>
I will update it, thanks!

> > (gdb) lx-version
> > L(gdb)
> >
> > This can be fixed by casting 'linux_banner' as (char *).
> > (gdb) lx-version
> > Linux version 4.19.0-rc1+ (changbin@acer) (gcc version 7.3.0 (Ubuntu 7.3.0-16ubuntu3)) #21 SMP Sat Sep 1 21:43:30 CST 2018
> >
> > gdb 7.4 seems to be no such issue.
> >
> > Signed-off-by: Du Changbin <changbin.du@gmail.com>
> > ---
> >   scripts/gdb/linux/proc.py | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/scripts/gdb/linux/proc.py b/scripts/gdb/linux/proc.py
> > index 086d27223c0c..0aebd7565b03 100644
> > --- a/scripts/gdb/linux/proc.py
> > +++ b/scripts/gdb/linux/proc.py
> > @@ -41,7 +41,7 @@ class LxVersion(gdb.Command):
> >       def invoke(self, arg, from_tty):
> >           # linux_banner should contain a newline
> > -        gdb.write(gdb.parse_and_eval("linux_banner").string())
> > +        gdb.write(gdb.parse_and_eval("(char *)linux_banner").string())
> >   LxVersion()
> >
>
> Looks good to me otherwise.
>
> Jan
>
> --
> Siemens AG, Corporate Technology, CT RDA IOT SES-DE
> Corporate Competence Center Embedded Linux

--
Thanks,
Du Changbin