Re: ld prints "mangled" error message

On Mon, Mar 28, 2022 at 06:46:03PM -0400, Gyorgy Matyasfalvi wrote:
> Hello,
> 
> It looks to me that undefined references to functions taking const pointers
> are reported with a mangled function signature.
> 
> ```
>     ld: warning: cannot find entry symbol _start; defaulting to
> 0000000000401000
>     ld: main.o: in function `main':
>     main.cpp:(.text+0x1f): undefined reference to `pc(char const*)'
> ```
> 
> I think `pc(char const*)' should be `pc(const char*)'.

Why do you think that?  'char const *' and 'const char *' are two
alternative spellings of the same type in both C and C++.  At the
point where the linker cares about type compatibility, the obejct file
format does not store the spelling used in the source code (*), but
merely a condensed representation of the type (thanks to the magic of
name mangling).  So when the linker has to output an error message, it
reconstitutes a canonical form for spelling the underlying type it is
reporting about, as read from the object file, with no visibility into
which of several possible source code spellings were in use when
building the object file.

(*) The object file format might store the source-code spelling of the
type in a debug section, but that's a different (and optional) portion
of the object file, in relation to the portion of the file where the
linker is trying to satisfy linkage to a mangled name representing a
specific C++ type.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
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