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Re: Built-in type handling in gdb
- From: vijay nag <vijunag at gmail dot com>
- To: Doug Evans <dje at google dot com>
- Cc: "gdb at sourceware dot org" <gdb at sourceware dot org>
- Date: Mon, 19 May 2014 16:29:57 +0530
- Subject: Re: Built-in type handling in gdb
- Authentication-results: sourceware.org; auth=none
- References: <CAKhyrx8PRG_OkZtAN=r-1=f9oFm21ZHcC=yO1eyJQXqxZOJFiw at mail dot gmail dot com> <CADPb22Rr7=Nc=NDaTJPgrgZGT-3OpqWuApk_ONnEhGBPuacofA at mail dot gmail dot com>
On Fri, May 16, 2014 at 10:54 PM, Doug Evans <firstname.lastname@example.org> wrote:
> On Thu, May 15, 2014 at 1:35 AM, vijay nag <email@example.com> wrote:
>> Hello GDB,
>> I have a simple GDB script to walk through the heap given a core file.
>> The data types used in the scripts are all primitive C data types and
>> any non primitive user defined data types have been avoided to speed
>> up the execution. In the older version of GDB(say gdb-7.0) this script
>> finished execution in a jiffy, the new gdb is way too slow in
>> execution. I built gdb-7.0/7.6 from source and observed the difference
>> in execution.
>> As part of this commit "NEWS: Mention OpenCL C language support
>> 2010-11-05 Ken Werner
>> * c-exp.y: Lookup the primitive types instead of referring to the
>> builtins.", parse_type macro(get from builtin) has been changed to a
>> function call lookup_signed_typename(). This function seems to be
>> doing an exhaustive global/static symbols search even for a C
>> primitive data type(say int) there by consuming plenty of CPU cycles.
>> Should we be doing this exhaustive search of data types from the
>> binary file even for basic C primitive data types ?
> I agree the current situation is less then stellar.
> There is one catch that needs to be handled that isn't necessarily obvious.
> The size of each primitive type is specific to each .o file (CU in
> DWARF parlance).
> E.g., If I compile foo.c with -fshort-double then sizeof(double) == 4 in foo.o.
> While it's difficult for an app to make this work in general, gdb
> should still support it.
> The order in which types should be looked up is:
> - current CU
> - builtin type
> - globally (fallback in the case of base types)
> [N.B. that's a qualified "globally" as base types live in gdb's STATIC_BLOCK]
> I think the fix isn't that hard, but it will require some changes to
> symbol lookup of base types.
> It's on my TODO list, but I'm happy to guide anyone through the
> changes required.
Is the below patch plausible ? I have basically changed the look-up
order of user defined data type and primitive data type.
diff --git a/systemsw/tools/src/gdb-7.6/gdb/gdbtypes.c
index 12730d7..8211b35 100644
@@ -1201,13 +1201,14 @@ lookup_typename (const struct language_defn *language,
struct symbol *sym;
struct type *type;
+ type = language_lookup_primitive_type_by_name (language, gdbarch, name);
+ if (type)
+ return type;
sym = lookup_symbol (name, block, VAR_DOMAIN, 0);
if (sym != NULL && SYMBOL_CLASS (sym) == LOC_TYPEDEF)
return SYMBOL_TYPE (sym);
- type = language_lookup_primitive_type_by_name (language, gdbarch, name);
- if (type)
- return type;