Concatenating LazyStrings

Concatenating LazyStrings

[David Blaikie]

If I've got a pretty printer (for instance, for llvm's Twine type (
https://github.com/llvm/llvm-project/blob/6d03227c16ee1950db0e1aa05fbc3201770248eb/llvm/utils/gdb-scripts/prettyprinters.py#L354
+ https://llvm.org/doxygen/classllvm_1_1Twine.html ) that wants to pretty
print a string made up of other strings (from other pretty printers) - how
would I do that?

Specifically, I can't figure out how to correctly concatenate a gdb
LazyString value with another string. (even if I have to stringify the
LazyString (making it unlazy) in the process - calling ".value()" on the
LazyString doesn't seem to be enough - I can't seem to figure out how to
to-string-ify that resulting gdb Value (it doesn't have a pretty printer
that I can find - nor a to_string/str/string() function) to then
concatenate it with another string)

Re: Concatenating LazyStrings

[Luke Drummond]

Hi David

On Fri Nov 5, 2021 at 3:14 AM GMT, David Blaikie via Gdb wrote:
> If I've got a pretty printer (for instance, for llvm's Twine type (
> https://github.com/llvm/llvm-project/blob/6d03227c16ee1950db0e1aa05fbc3201770248eb/llvm/utils/gdb-scripts/prettyprinters.py#L354
> + https://llvm.org/doxygen/classllvm_1_1Twine.html ) that wants to
> pretty
> print a string made up of other strings (from other pretty printers) -
> how
> would I do that?
>
> Specifically, I can't figure out how to correctly concatenate a gdb
> LazyString value with another string. (even if I have to stringify the
> LazyString (making it unlazy) in the process - calling ".value()" on the
> LazyString doesn't seem to be enough - I can't seem to figure out how to
> to-string-ify that resulting gdb Value (it doesn't have a pretty printer
> that I can find - nor a to_string/str/string() function) to then
> concatenate it with another string)


`LazyString.value().format_string()` might be what you want. I've also found the
python builtin `str()` function to be usable in many places.

https://sourceware.org/gdb/onlinedocs/gdb/Values-From-Inferior.html#Values-From-Inferior

has the documentation if you haven't already seen it.

As an example, here's how I format an enumeration that's made up of bit-flags:

	def fmt_flags_enum(enum_type, val):
			val = int(val)
			return ' | '.join(
					gdb.Value((1 << x) & val).cast(enum_type).format_string()
					for x in range(val.bit_length())
					if (1 << x) & val
			)


The `format_string()` converts the individual enumerators into a string that
python can concatenate with `str.join`.

Hope that helps.

All the Best

Luke


-- 
Codeplay Software Ltd.
Company registered in England and Wales, number: 04567874
Registered office: Regent House, 316 Beulah Hill, London, SE19 3HF

Re: Concatenating LazyStrings

[David Blaikie]

Oh, huh, just gdb::Value's "string()" worked for me in the end - I was
dealing with some other layers of indirection/existing oddities in my
pretty printer codebase that had complicated things.

Thanks for the nudges in the right direction!

On Fri, Nov 5, 2021 at 5:22 AM Luke Drummond <luke.drummond@codeplay.com>
wrote:

> Hi David
>
> On Fri Nov 5, 2021 at 3:14 AM GMT, David Blaikie via Gdb wrote:
> > If I've got a pretty printer (for instance, for llvm's Twine type (
> >
> https://github.com/llvm/llvm-project/blob/6d03227c16ee1950db0e1aa05fbc3201770248eb/llvm/utils/gdb-scripts/prettyprinters.py#L354
> > + https://llvm.org/doxygen/classllvm_1_1Twine.html ) that wants to
> > pretty
> > print a string made up of other strings (from other pretty printers) -
> > how
> > would I do that?
> >
> > Specifically, I can't figure out how to correctly concatenate a gdb
> > LazyString value with another string. (even if I have to stringify the
> > LazyString (making it unlazy) in the process - calling ".value()" on the
> > LazyString doesn't seem to be enough - I can't seem to figure out how to
> > to-string-ify that resulting gdb Value (it doesn't have a pretty printer
> > that I can find - nor a to_string/str/string() function) to then
> > concatenate it with another string)
>
>
> `LazyString.value().format_string()` might be what you want. I've also
> found the
> python builtin `str()` function to be usable in many places.


>
> https://sourceware.org/gdb/onlinedocs/gdb/Values-From-Inferior.html#Values-From-Inferior
>
> has the documentation if you haven't already seen it.
>
> As an example, here's how I format an enumeration that's made up of
> bit-flags:
>
>         def fmt_flags_enum(enum_type, val):
>                         val = int(val)
>                         return ' | '.join(
>                                         gdb.Value((1 << x) &
> val).cast(enum_type).format_string()
>                                         for x in range(val.bit_length())
>                                         if (1 << x) & val
>                         )
>
>
> The `format_string()` converts the individual enumerators into a string
> that
> python can concatenate with `str.join`.
>
> Hope that helps.
>
> All the Best
>
> Luke
>
>
> --
> Codeplay Software Ltd.
> Company registered in England and Wales, number: 04567874
> Registered office: Regent House, 316 Beulah Hill, London, SE19 3HF
>