Default target wide character set
Alexey Feldgendler
alexeyf@opera.com
Tue Sep 15 14:12:00 GMT 2009
Hello, all.
I'm Alexey Feldgendler, a developer in a software company that uses gdb to
debug on *nix systems. I got assigned part-time to contribute to gdb,
mostly by fixing bugs that affect us, but also to implement new features.
Because I'm new to gdb internals, I'm trying to be very careful about
making anything but trivial fixes like <> for now, so I'd like to discuss
with you something I'm trying to achieve. Thank you in advance for your
time.
Currently, UCS-4 is the default target wide character set. However, what
this setting is really used for is handling of wide character strings,
i.e. sequences of wide characters, which in C[++] are represented by the
type wchar_t. By default, gcc indeed considers wchar_t 4 bytes wide, but
it has an option to make wchar_t 2 bytes wide (-fshort-wchar). When this
option is used, the default setting for the target wide character set
becomes wrong.
Looking at charset_for_string_type(), it seems to handle C_STRING_16 and
C_STRING_32 sort of correctly based on the character width. However, for
C_WIDE_STRING it simply uses target_wide_charset(), no matter whether it's
reasonable or not.
I have two alternative ideas for how to tackle this problem.
A. Have the default target wide character set depend on the size of the
type named wchar_t. If I understand it correctly, in this case the default
needs to be updated then when the symbol table gets loaded. Of course, any
user-specified value should override the computed default. There should
also be some way to reset the option to its dynamic default.
Side question: how does gdb figure out sizeof(wchar_t)? Does it come from
the symbol table or from elsewhere?
B. Have charset_for_string_type() check after calling
target_wide_charset() whether the width of the returned character set
matches the width of the actual string type, and use fallback similar to
what's done for C_STRING_16 and C_STRING_32 if it doesn't. By width of the
character set I mean the smallest possible width of a character in it,
that would be e.g. 1 for UTF-8 and 2 for UCS-2. In this case, what âshow
charsetâ shows sometimes won't match what's actually used to print a
wchar_t[] string.
What do you think of options A and B? Or is there maybe another possiblity
that I'm overlooking?
--
Alexey Feldgendler <alexeyf@opera.com>
Software Developer, Desktop Platform/Delivery Team, Opera Software ASA
[ICQ: 115226275] http://my.opera.com/feldgendler/
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