Re: Robustifying pretty-printers

Vladimir Prus
2009-06-13T10:21:24Z

On Saturday 13 June 2009 you wrote:

>
> While playing with pretty-printers and KDevelop, I've got GDB
> to "hang", with the below backtrace:
>
> (gdb) where
> #0 0xb7d0ed2a in strcmp () from /lib/tls/i686/cmov/libc.so.6
> #1 0x081be1a7 in install_variable (var=0x191b0620) at /home/ghost/Work/CodeSourcery/Projects/egdb/gdb-cvs/gdb/varobj.c:1731
> #2 0x081beef7 in create_child_with_value (parent=0x8a6e158, index=514255, name=0xb7bf8e14 "[514255]", value=0x191b03d0)
> at /home/ghost/Work/CodeSourcery/Projects/egdb/gdb-cvs/gdb/varobj.c:1859
>
> The '514255' above is sufficient to understand what happened. Our beloved GCC fails to emit
> proper debug info, therefore a vector is considered in scope before constructor is executed,
> and the vector is full of random bits.
>
> Now, what are the best strategies for fix this (assuming GCC won't be
> fixed for 10 years to come)? One approach is to make IDE check at what
> line the variable is declared, and don't try to pretty-print it unless
> the current line is above that. Alternatively, we might need to revive
> the code to limit the number of children to fetch, and use some reasonable
> limit, like 10. Comments?

In fact, there's yet another case:

class StdStringPrinter:
"Print a std::basic_string of some kind"

def __init__(self, encoding, val):
self.encoding = encoding
self.val = val

def to_string(self):
# Look up the target encoding as late as possible.
encoding = self.encoding
if encoding == 0:
encoding = gdb.parameter('target-charset')
elif encoding == 1:
encoding = gdb.parameter('target-wide-charset')
elif isinstance(encoding, WideEncoding):
encoding = encoding.value
return self.val['_M_dataplus']['_M_p'].string(encoding)

I am not quite sure where the 'string' method is defined, so the
question is -- assuming I know the expected size of the string.
How do I make the 'string' method not to fetch more than that?

- Volodya