Re: [PATCH] Fix crash when loading a core with unexpected register section size

[Antoine Tremblay <antoine dot tremblay at ericsson dot com>]

Pedro Alves writes:

> On 01/26/2017 01:17 PM, Antoine Tremblay wrote:
>> When loading a core without an executable like so:
>> gdb --core core for example often the gdbarch won't contain the
>> iterate_over_regset_sections method.
>
> Can you give an example?  That'd help a lot understand the issue
> better.
>

I can't share the core that I have that reproduced this :( 

> Also, please add a line break, ""s and/or punctuation to make
> the command stand out more from the rest of the sentence.
> For example:
>
> When loading a core without an executable like so:
>  $ gdb --core core
> for example, often the gdbarch won't contain the
> iterate_over_regset_sections method.  For example arch-foo.
>

OK.

>> 
>> This will generate a call to get_core_register_section with a NULL regset
>> like at corelow.c:628
>> 
>> get_core_register_section (regcache, NULL, ".reg", 0, 0, "general-purpose", 1);
>> 
>> However a check for REGSET_VARIABLE_SIZE in get_core_register_section
>> assumes that regset is != NULL thus leading to a crash with this backtrace:
>> 
>> (gdb) bt
>> #0  0x000000000065907b in get_core_register_section
>>     (regcache=regcache@entry=0x2c26260, regset=regset@entry=0x0,
>>     name=name@entry=0xdbf7b2 ".reg", min_size=min_size@entry=0,
>>     which=which@entry=0, human_name=human_name@entry=0xdbac28
>>     "general-purpose", required=1)
>>     at ../../gdb/corelow.c:542
>> #1  0x0000000000659b70 in get_core_registers (ops=<optimized out>,
>>     regcache=0x2c26260, regno=<optimized out>) at ../../gdb/corelow.c:628
>> #2  0x000000000076e5fb in target_fetch_registers
>>     (regcache=regcache@entry=0x2c26260, regno=regno@entry=15) at ../../gdb/target.c:3590
>> 
>> Note that commit: f962539ad23759af4ba8f7eece1946fdc2f5087 
>
> Please always paste the commit's subject as well, to make
> it easier for us poor humans to quickly tell what the commit
> was about without having to go to a terminal.  The Linux guideline
> is to put it in parens:
>
>  Note that commit f962539ad23759 ("Warn if core file register
>  section is larger than expected") introduced [...]
>
> I personally like that style.
>

OK thanks,

> introcuded this
>
> (typo)
>

Indeed.
>> issue. Thus releases > 7.8.2 are affected.
>> 
>> This patch fixes this crash by adding a check for regset existence before
>> running the condition.
>> 
>> gdb/ChangeLog:
>> 
>> 	* corelow.c (get_core_register_section): Check for regset
>>                    existance before checking for REGSET_VARIABLE_SIZE.
>
> Indentation.  "existence".
>

Yes oops.

>> ---
>>  gdb/corelow.c | 7 ++++++-
>>  1 file changed, 6 insertions(+), 1 deletion(-)
>> 
>> diff --git a/gdb/corelow.c b/gdb/corelow.c
>> index a075d9e..f43f730 100644
>> --- a/gdb/corelow.c
>> +++ b/gdb/corelow.c
>> @@ -515,6 +515,7 @@ get_core_register_section (struct regcache *regcache,
>>    struct bfd_section *section;
>>    bfd_size_type size;
>>    char *contents;
>> +  bool variable_size_section = false;
>
> No need to initialize by default when you're always going to
> initialize it again below.  Or declare on first use and avoid
> the issue entirely.
>

Indeed. fixed.

V2 coming in next mail.