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

[Andrew Burgess <aburgess@redhat.com>]

tdevries <tdevries@suse.de> writes:

> On 2022-12-20 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?
>
> LGTM.
>
> Though I wonder if we can make do with being less precise, and just do 
> something like:
> ...
> proc assert_shared_library_debug_not_fully_expanded {} {
>      gdb_test_lines "maint print objfiles $::libname" "" \
>          "Object file \[^\r\n\]*$::libname" \
>          -re-not "Symtabs:"
> }
> ...
>

Thanks for that suggestion Tom, that really is much better that what I
had.

I've taken your suggestion and pushed the fix to master.  My final patch
is below.

Thanks,
Andrew

---

commit 3a98808c164b36c7023bd80fc6b019cbe6274365
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 single 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..30e224fb439 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
@@ -46,46 +47,10 @@ if {[readnow]} {
 # library has been fully expanded or not.  Return true if the debug
 # 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" {
-	    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"
-	    }
-	    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"
-	    }
-	    exp_continue
-	}
-	-re "^(\[^\r\n\]+):\r\n\r\n" {
-	    set libname $expect_out(1,string)
-	    if {$libname == $::objdso} {
-		set library_expanded "yes"
-	    }
-	    exp_continue
-	}
-	-re "^$::gdb_prompt $" {
-	    gdb_assert {[string equal $library_expanded "yes"] \
-			    || [string equal $library_expanded "no"]} \
-		$gdb_test_name
-	}
-	-re "^(\[^\r\n:\]*)\r\n" {
-	    exp_continue
-	}
-    }
-
-    return [expr $library_expanded == "no"]
+proc assert_shared_library_debug_not_fully_expanded {} {
+    gdb_test_lines "maint print objfiles $::libname" "" \
+	"Object file \[^\r\n\]*$::libname" \
+	-re-not "Symtabs:"
 }
 
 foreach_with_prefix type_name {"short" "int" "long" "char"} {
@@ -93,7 +58,7 @@ foreach_with_prefix type_name {"short" "int" "long" "char"} {
 	with_test_prefix "before sizeof expression" {
 	    # Check that the debug information for the shared library has
 	    # not yet been read in.
-	    gdb_assert { [shared_library_debug_not_fully_expanded] }
+	    assert_shared_library_debug_not_fully_expanded
 	}
 
 	# Evaluate a sizeof expression for a builtin type.  At one point GDB
@@ -106,7 +71,7 @@ foreach_with_prefix type_name {"short" "int" "long" "char"} {
 	with_test_prefix "after sizeof expression" {
 	    # Check that the debug information for the shared library has not
 	    # yet been read in.
-	    gdb_assert { [shared_library_debug_not_fully_expanded] }
+	    assert_shared_library_debug_not_fully_expanded
 	}
     }
 }