Breakpoint troubles on typedefs

Breakpoint troubles on typedefs

[Martin Schröder]

Hello everyone.


I seem to have found a bug / feature in GDB 7.2 for C++. The problem is that 
typedefs are not converted to their base type when one tries to set a 
breakpoint into a function that has a typedef'd type as parameter.

Here's a simple program that triggers this bug:

main.cpp
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#include <string>

typedef std::string foo;

void calltest(foo val) {}

int main() {
    calltest(foo(""));
}
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Compiled with: "g++ -O0 -g main.cpp -o a.out"

Now, when you start the program with gdb 7.2, you'll get the following 
whatis replies:

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(gdb) whatis foo
type = std::string
(gdb) whatis calltest
type = void (foo)
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But now, try to set a breakpoints. Once with "foo" and once with 
"std::string"; which should be equal, as whatis has just told us.

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(gdb) break calltest(foo)
Breakpoint 1 at 0x80485e7: file main.cpp, line 5.

(gdb) break calltest(std::string)
   Can't find member of namespace, class, struct, or union
   named "calltest(std::string)"
   Hint: try 'calltest(std::string)<TAB> or
   'calltest(std::string)<ESC-?>
   (Note leading single quote.)
Make breakpoint pending on future shared library load? (y or [n]) n
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So, you might try to see the expansion. This is what GDB returns on Tab:

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(gdb) break calltest<TAB>
[...]
calltest(foo)
calltest(std::basic_string<char, std::char_traits<char>, 
std::allocator<char> >)
[...]
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So, among the massiv amounts of text, we find both foo, and the full 
"std::string" typedef-expansion. Okay, so we try to set the breakpoint 
accordingly:

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(gdb) whatis calltest(std::string)
type = void (foo)

(gdb) whatis calltest(std::basic_string<char,
        std::char_traits<char>, std::allocator<char> >)
type = void (foo)

(gdb) break calltest(std::basic_string<char,
        std::char_traits<char>, std::allocator<char> >)
Can't find member of namespace, class, struct, or union named
[...]
Make breakpoint pending on future shared library load? (y or [n]) n
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So ... what this tells me is that "whatis" reads the symbol table correctly, 
but break somehow doesn't.


But wait, it gets even better. Now quit GDB and restart it. This is what you 
get when you issue the "break" as the very first command:

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(gdb) break calltest(foo)
Function "calltest(foo)" not defined.
Make breakpoint pending on future shared library load? (y or [n]) n

(gdb) whatis foo
type = std::string

(gdb) break calltest(foo)
Breakpoint 1 at 0x80485e7: file main.cpp, line 5.
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Interesting, isn't it? Do note that you can substitute the "whatis" with a 
range of commands; for example "break main", or "list" and the second call 
will still work. But not all commands, observe:

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(gdb) break calltest(foo)
Function "calltest(foo)" not defined.
Make breakpoint pending on future shared library load? (y or [n]) n

(gdb) break calltest(foo)
Function "calltest(foo)" not defined.
Make breakpoint pending on future shared library load? (y or [n]) n

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Furthermore, starting with a fresh GDB will also change what the 
tab-expansion shows. Instead of lots and lots of types, it shows only the 
two "calltest" function entries; but it shows "std::string" instead of the 
full typedef-expansion for std::string in the second entry.


Anyway, here's the platform and program versions I used for testing:

OS: Ubuntu 10.10
gdb: 7.2-ubuntu
g++: (Ubuntu/Linaro 4.4.4-14ubuntu5) 4.4.5


I've tested the same program with an older, self-compiled GDB 7.1, and there 
I get this:

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(gdb) break calltest(foo)
Function "calltest(foo)" not defined.
Make breakpoint pending on future shared library load? (y or [n]) n

(gdb) whatis foo
type = std::string

(gdb) break calltest(foo)
Function "calltest(foo)" not defined.
Make breakpoint pending on future shared library load? (y or [n]) n

(gdb) break calltest(std::string)
Breakpoint 1 at 0x8048627: file main.cpp, line 5.

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Basically, I have no clue what could trigger this strange behaviour. It 
almost seems to me as if GDB 7.2 added support for typedef'd variables, but 
broke the "break" statement in a way that causes it to not read the 
symbol-table correctly anymore, but I could be a mile off with that 
suspicion.


Any help would be appreciated, thanks,
    Martin Schröder. 

Re: Breakpoint troubles on typedefs

[Tom Tromey]

>>>>> "Martin" == Martin Schröder <gschroeder@onlinehome.de> writes:

Martin> I seem to have found a bug / feature in GDB 7.2 for C++. The problem
Martin> is that typedefs are not converted to their base type when one tries
Martin> to set a breakpoint into a function that has a typedef'd type as
Martin> parameter.

Could you file this in GDB's bugzilla?

A group of us are actively working on C++-related problems in GDB.  It
is best for us if bugs are in bugzilla so we don't miss any.

thanks,
Tom

Re: Breakpoint troubles on typedefs

[Martin Schröder]

Tom Tromey wrote:
>>>>>> "Martin" == Martin Schröder <gschroeder@onlinehome.de> writes:
>
>> I seem to have found a bug / feature in GDB 7.2 for C++. The
>> problem is that typedefs are not converted to their base type
>> when one tries to set a breakpoint into a function that has a
>> typedef'd type as Martin> parameter.
>>
>> Could you file this in GDB's bugzilla?
>>
>> A group of us are actively working on C++-related problems in
>> GDB. It is best for us if bugs are in bugzilla so we don't miss
>> any.

Sure, will do so tomorrow (it's past midnight where I hail from).



So long,
    Martin. 

Re: Breakpoint troubles on typedefs

[Martin Schröder]

Martin Schröder wrote:
> Tom Tromey wrote:
>>>>>>> "Martin" == Martin Schröder <gschroeder@onlinehome.de> writes:
>>
>>> I seem to have found a bug / feature in GDB 7.2 for C++. The
>>> problem is that typedefs are not converted to their base type
>>> when one tries to set a breakpoint into a function that has a
>>> typedef'd type as Martin> parameter.
>>>
>>> Could you file this in GDB's bugzilla?
>>>
>>> A group of us are actively working on C++-related problems in
>>> GDB. It is best for us if bugs are in bugzilla so we don't miss
>>> any.
>
> Sure, will do so tomorrow (it's past midnight where I hail from).
>

Here's the link to the bugzilla entry:

http://sourceware.org/bugzilla/show_bug.cgi?id=12266


So long,
    Martin.