Re: [PATCH 2/2] gdb/testsuite: new test for recent dwarf reader issue

[Luis Machado <luis.machado@arm.com>]

On 12/20/22 13:20, Andrew Burgess wrote:
> Andrew Burgess <aburgess@redhat.com> writes:
> 
>> tdevries <tdevries@suse.de> writes:
>>
>>> On 2022-12-19 13:52, Andrew Burgess via Gdb-patches wrote:
>>>> Luis Machado <luis.machado@arm.com> writes:
>>>>
>>>>> On 12/15/22 11:22, Andrew Burgess wrote:
>>>>>> Luis Machado <luis.machado@arm.com> writes:
>>>>>>
>>>>>>> Hi Andrew,
>>>>>>>
>>>>>>> On 12/9/22 19:24, Andrew Burgess via Gdb-patches wrote:
>>>>>>>> Tom Tromey <tom@tromey.com> writes:
>>>>>>>>
>>>>>>>>>>>>>> "Andrew" == Andrew Burgess via Gdb-patches
>>>>>>>>>>>>>> <gdb-patches@sourceware.org> writes:
>>>>>>>>>
>>>>>>>>> Thank you for doing this.
>>>>>>>>>
>>>>>>>>> Andrew>   - However, GDB checks each partial symbol using multiple
>>>>>>>>> languages,
>>>>>>>>> Andrew>     not just the current language (C in this case), so,
>>>>>>>>> when GDB
>>>>>>>>> Andrew>     checks using the C++ language, the symbol name is
>>>>>>>>> first demangled,
>>>>>>>>> Andrew>     the code that does this can be found
>>>>>>>>> Andrew>     lookup_name_info::language_lookup_name.  As the
>>>>>>>>> demangled form of
>>>>>>>>> Andrew>     'signed int' is just 'int', GDB then looks for any
>>>>>>>>> symbols with
>>>>>>>>> Andrew>     the name 'int', most partial symtabs will contain such
>>>>>>>>> a symbol,
>>>>>>>>> Andrew>     so GDB ends up expanding pretty much every symtab.
>>>>>>>>>
>>>>>>>>> It's a pedantic point but what happens here is name
>>>>>>>>> canonicalization,
>>>>>>>>> not demangling.  Demangling is just used to refer to the
>>>>>>>>> translation
>>>>>>>>> from a name like "_Zmumble" to "something::else" -- that is, the
>>>>>>>>> input
>>>>>>>>> is a linkage name and the output is a C++ name.  Canonicalization
>>>>>>>>> takes
>>>>>>>>> a C++ name as input and returns the standard form, basically
>>>>>>>>> dealing
>>>>>>>>> with the fact that C++ (and as we discovered, C) has multiple
>>>>>>>>> possible
>>>>>>>>> spellings for some symbols.
>>>>>>>>
>>>>>>>> Please, be pedantic.  My goal here was to better understand this
>>>>>>>> code,
>>>>>>>> there's no point me understanding it wrong.
>>>>>>>>
>>>>>>>> I'll reword that paragraph.
>>>>>>>>
>>>>>>>> Thanks for taking a look.
>>>>>>>>
>>>>>>>> Andrew
>>>>>>>>
>>>>>>>
>>>>>>> I'm not saying you should investigate this, as it is a new test, but
>>>>>>> I'm getting a lot of these messages for this test:
>>>>>>>
>>>>>>> ERROR: internal buffer is full.
>>>>>>
>>>>>> Happy to take a look at the problem.
>>>>>>
>>>>>> I guess the issue is coming from the gdb_test_multiple that I use in
>>>>>> the
>>>>>> new test script.
>>>>>>
>>>>>> I'm tried to write patterns that match and discard all the lines as
>>>>>> they
>>>>>> arrive from GDB.  I guess you are seeing a pattern that I am not for
>>>>>> some reason.
>>>>>>
>>>>>> Could you run just this test and attach the gdb.log file and I'll
>>>>>> take a
>>>>>> look.  I probably just need to tweak one of the patterns a little.
>>>>>>
>>>>>> Thanks,
>>>>>> Andrew
>>>>>>
>>>>>
>>>>> I briefly looked into this. The problem seems to arise from the fact
>>>>> that sometimes we don't have multiple lines for the "info sources"
>>>>> output.
>>>>>
>>>>> Some sections are output in a single line. For example, one of them
>>>>> has 133K characters. But each entry seems to be separated by a comma
>>>>> character:
>>>>>
>>>>> ./elf/./elf/rtld.c, ./elf/../include/rtld-malloc.h,
>>>>> ./elf/../sysdeps/generic/ldsodefs.h,
>>>>> ./elf/../sysdeps/aarch64/dl-machine.h, ...
>>>>
>>>> Ahh, that would explain it.  We don't appear to use 'info sources' that
>>>> frequently in the testsuite.  I wonder if you are also seeing failures
>>>> on those other tests?
>>>>
>>>>    gdb.asm/asm-source.exp
>>>>    gdb.dwarf2/dup-psym.exp
>>>>    gdb.dwarf2/dw2-filename.exp
>>>>
>>>>> It might be best (for the testsuite) if gdb outputs this data across
>>>>> more lines.
>>>>
>>>> The other option might be to extend 'info sources' to allow filtering
>>>> based on the objfile name, then we can use this in the testsuite to
>>>> limit the output...
>>>>
>>>> ... or I wonder if we could trick GDB by setting the width to something
>>>> small, the I guess the lines would be broken after the ',' characters.
>>>>
>>>> I'll have a play and see what I can come up with.
>>>>
>>>
>>> I also ran into this issue on ubuntu 22.04.1 x86_64.
>>>
>>> AFAIK, the way we usually test for this type of information is "maint
>>> print objfile", which is less verbose, and doesn't have long lines.
>>
>> I'm looking at this issue today, I'll give 'maint print objfile' a go.
>> Thanks for the suggestion.
> 
> I was able to reproduce the buffer overflow errors.  The patch below
> addresses the issue for me.
> 
> Thoughts?
> 
> Thanks,
> Andrew
> 
> ---
> 
> commit e1f51c1b3b37d96e679fa2698eb83a6a3a05eb53
> Author: Andrew Burgess <aburgess@redhat.com>
> Date:   Tue Dec 20 12:51:50 2022 +0000
> 
>      gdb/testsuite: fix buffer overflow in gdb.base/signed-builtin-types.exp
>      
>      In commit:
>      
>        commit 9f50fe0835850645bd8ea9bb1efe1fe6c48dfb12
>        Date:   Wed Dec 7 15:55:25 2022 +0000
>      
>            gdb/testsuite: new test for recent dwarf reader issue
>      
>      A new test (gdb.base/signed-builtin-types.exp) was added that made use
>      of 'info sources' to figure out if the debug information for a
>      particular object file had been fully expanded or not.  Unfortunately
>      some lines of the 'info sources' output can be very long, this was
>      observed on some systems where the debug information for the
>      dynamic-linker was installed, in this case, the list of source files
>      associated with the dynamic linker was so long it would cause expect's
>      internal buffer to overflow.
>      
>      This commit switches from using 'info sources' to 'maint print
>      objfile', the output from the latter command is more compact, but
>      also, can be restricted to a named object file.
>      
>      With this change in place I am no longer seeing buffer overflow errors
>      from expect when running gdb.base/signed-builtin-types.exp.
> 
> diff --git a/gdb/testsuite/gdb.base/signed-builtin-types.exp b/gdb/testsuite/gdb.base/signed-builtin-types.exp
> index e9784330fee..fdb9251758e 100644
> --- a/gdb/testsuite/gdb.base/signed-builtin-types.exp
> +++ b/gdb/testsuite/gdb.base/signed-builtin-types.exp
> @@ -21,7 +21,8 @@ standard_testfile .c -lib.c
>   
>   # Compile the shared library.
>   set srcdso [file join $srcdir $subdir $srcfile2]
> -set objdso [standard_output_file lib${gdb_test_file_name}.so]
> +set libname "lib${gdb_test_file_name}.so"
> +set objdso [standard_output_file $libname]
>   if {[gdb_compile_shlib $srcdso $objdso {debug}] != ""} {
>       untested "failed to compile dso"
>       return -1
> @@ -47,45 +48,39 @@ if {[readnow]} {
>   # information has NOT been fully expanded (which is what we want for this
>   # test).
>   proc shared_library_debug_not_fully_expanded {} {
> -    set library_expanded ""
> -    gdb_test_multiple "info sources" "" {
> -	-re "^info sources\r\n" {
> +    set not_expanded true
> +    gdb_test_multiple "maint print objfiles $::libname" "" {
> +	-re "^maint print objfiles \[^\r\n\]+\r\n" {
>   	    exp_continue
>   	}
> -	-re "^(\[^\r\n\]+):\r\n\\(Full debug information has not yet been read for this file\\.\\)\r\n\r\n" {
> -	    set libname $expect_out(1,string)
> -	    if {$libname == $::objdso} {
> -		set library_expanded "no"
> -	    }
> +
> +	-re "^\\s*\r\n" {
> +	    exp_continue
> +	}
> +
> +	-re "^Object file \[^\r\n\]+\r\n" {
>   	    exp_continue
>   	}
> -	-re "^(\[^\r\n\]+):\r\n\\(Objfile has no debug information\\.\\)\r\n\r\n" {
> -	    set libname $expect_out(1,string)
> -	    if {$libname == $::objdso} {
> -		# For some reason the shared library has no debug
> -		# information, this is not expected.
> -		set library_expanded "missing debug"
> -	    }
> +
> +	-re "^Cooked index in use\r\n" {
>   	    exp_continue
>   	}
> -	-re "^(\[^\r\n\]+):\r\n\r\n" {
> -	    set libname $expect_out(1,string)
> -	    if {$libname == $::objdso} {
> -		set library_expanded "yes"
> -	    }
> +
> +	-re "^Symtabs:\r\n" {
> +	    set not_expanded false
>   	    exp_continue
>   	}
> +
>   	-re "^$::gdb_prompt $" {
> -	    gdb_assert {[string equal $library_expanded "yes"] \
> -			    || [string equal $library_expanded "no"]} \
> -		$gdb_test_name
> +	    pass $gdb_test_name
>   	}
> -	-re "^(\[^\r\n:\]*)\r\n" {
> +
> +	-re "^\[^\r\n\]+\r\n" {
>   	    exp_continue
>   	}
>       }
>   
> -    return [expr $library_expanded == "no"]
> +    return $not_expanded
>   }
>   
>   foreach_with_prefix type_name {"short" "int" "long" "char"} {
> 

LGTM, and it fixes things for me as well. Thanks a lot for looking into this.