[llvm] r335561 - [gdb] Escape unprintable bytes in SmallString and StringRef

[Fāng-ruì Sòng via llvm-commits]

On Wed, Nov 3, 2021 at 2:23 PM David Blaikie <dblaikie at gmail.com> wrote:
>
> Hey Ray - do you recall what the motivation for this patch was/is? I ask because this breaks gdb's ability to truncate long strings (which means printing out data structures with StringRefs that refer to, for instance, the entire contents of an object/executable, or of a section in such a file - is unfortunate/locks up the debugger for ages printing things out) and it looks like gdb escapes unprintable characters itself, without the need to do this manually so far as I can tell?

It's been 3 years so I cannot remember. If I made the change, likely
because gdb at that time did not display strings correctly and this
commit fixed the problem.
It's possible that gdb's behavior changed or somehow the commit's
behavior becomes harmful now.

I think I do notice some string stuff does not look pretty, but
haven't spent time investigating the problem.

> On Mon, Jun 25, 2018 at 5:46 PM Fangrui Song via llvm-commits <llvm-commits at lists.llvm.org> wrote:
>>
>> Author: maskray
>> Date: Mon Jun 25 17:41:49 2018
>> New Revision: 335561
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=335561&view=rev
>> Log:
>> [gdb] Escape unprintable bytes in SmallString and StringRef
>>
>> Modified:
>>     llvm/trunk/utils/gdb-scripts/prettyprinters.py
>>
>> Modified: llvm/trunk/utils/gdb-scripts/prettyprinters.py
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/utils/gdb-scripts/prettyprinters.py?rev=335561&r1=335560&r2=335561&view=diff
>> ==============================================================================
>> --- llvm/trunk/utils/gdb-scripts/prettyprinters.py (original)
>> +++ llvm/trunk/utils/gdb-scripts/prettyprinters.py Mon Jun 25 17:41:49 2018
>> @@ -11,6 +11,8 @@ class Iterator:
>>    def children(self):
>>      return self
>>
>> +def escape_bytes(val, l):
>> +  return '"' + val.string(encoding='Latin-1', length=l).encode('unicode_escape').decode() + '"'
>>
>>  class SmallStringPrinter:
>>    """Print an llvm::SmallString object."""
>> @@ -21,10 +23,7 @@ class SmallStringPrinter:
>>    def to_string(self):
>>      begin = self.val['BeginX']
>>      end = self.val['EndX']
>> -    return begin.cast(gdb.lookup_type("char").pointer()).string(length = end - begin)
>> -
>> -  def display_hint (self):
>> -    return 'string'
>> +    return escape_bytes(begin.cast(gdb.lookup_type('char').pointer()), end - begin)
>>
>>  class StringRefPrinter:
>>    """Print an llvm::StringRef object."""
>> @@ -33,10 +32,7 @@ class StringRefPrinter:
>>      self.val = val
>>
>>    def to_string(self):
>> -    return self.val['Data'].string(encoding='Latin-1', length=self.val['Length'])
>> -
>> -  def display_hint (self):
>> -    return 'string'
>> +    return escape_bytes(self.val['Data'], self.val['Length'])
>>
>>  class SmallVectorPrinter:
>>    """Print an llvm::SmallVector object."""
>>
>>
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