Re: [PATCH V4] symlookup: improves symbol lookup when a file is specified.

[Pedro Alves <palves at redhat dot com>]

On 10/20/2017 03:28 PM, Simon Marchi wrote:
> On 2017-10-20 03:45 AM, Tedeschi, Walfred wrote:
>> Hi Simon,
>>
>> Thanks for your review!
>> For all the comment above I agree, Thanks again!
>>
>> For the one below there are different point of views. 
>> How I see it: Very few sane people will add a symbols in a shared library that
>> will collide like the case we presented here.  If one does so how can the debugger
>> help?
> 
> I think one usual use case is plugins implemented with shared library.  Although
> the data symbols will commonly be static, and the plugin will only expose some
> function symbols.
> 
>> Providing the same value as the runtime or linker does? 
>> This one user already knows. 
>> Or providing what the debug information provides as value created by the library itself.
>> In final end both are right. :|
>>
>> But when specifying the scope if user is provided the value of the debug info it should
>> be easier to spot that there is something weird going on in the code.
> 
> I think what you just said summarizes the problem well and I think it makes sense.
> I just don't think I have enough experience about symbol handling to understand
> the situation fully.  Could another maintainer with more experience about symbols
> give the final ok?

I disagree.  Having
 (gdb) frame
 #0 0x000000000040073b in function () at source.c:22
 (gdb) print foo
and:
 (gdb) print 'source.c':foo

show different values when you're stopped in a function in
the source.c file would look inconsistent to me.

Actually, the patch introduces what looks like a related clear
regression to me.  With the print-file-var.exp test program, try
stepping into get_version_2, and printing the this_version_id
global.  And then type finish.  Vis:

 (gdb) s
 get_version_2 () at gdb.base/print-file-var-lib2.c:22
 22        return this_version_id;
 (gdb) p this_version_id
 $1 = 203
 (gdb) finish
 Run till exit from #0  get_version_2 () at gdb.base/print-file-var-lib2.c:22
 0x000000000040073b in main () at gdb.base/print-file-var-main.c:24
 24        int v2 = get_version_2 ();
 Value returned is $2 = 104
 (gdb) 

GDB says "203", while the program returns "104".
That looks like a bug to me.  I'd expect the print
to show me the current value of the variable in scope.

In current master (without the patch), we get:

 (gdb) s
 get_version_2 () at gdb.base/print-file-var-lib2.c:22
 22        return this_version_id;
 (gdb) p this_version_id
 $1 = 104
 (gdb) finish
 Run till exit from #0  get_version_2 () at gdb.base/print-file-var-lib2.c:22
 0x000000000040073b in main () at gdb.base/print-file-var-main.c:24
 24        int v2 = get_version_2 ();
 Value returned is $2 = 104

Thanks,
Pedro Alves