[PATCH 2/4] Fix incompatible struct declarations.

[Ralf Wildenhues]

* doc/libtool.texi (Dlpreopening): Remove broken documentation
of lt_dlsymbol and lt_dlsymlist.  Document typedef lt_dlsymlist
and symbol lt_preloaded_symbols according to the implementation.
* tests/demo/dlmain.c (lt_symlist): Make struct anonymous ...
(lt_dlsymlist): ... and typedef to this name.
(lt_preloaded_symbols, main): Adjust.
* tests/pdemo/longer_file_name_dlmain.c: Likewise.

Signed-off-by: Ralf Wildenhues <address@hidden>
---

Hello,

Contrary to popular belief, of these five,

A)
struct lt_symlist {
  const char *name;
  void *address;
};

B)
struct lt_dlsymlist {
  const char *name;
  void *address;
};

C)
typedef struct {
  const char *name;
  void *address;
} lt_dlsymlist;

D)
struct {
  const char *name;
  void *address;
} OBJECT;

E)
struct lt_dlsymbol {
  const char *name;
  void *address;
};

only (C) and (D) name pairwise compatible types, at least in C99 (in
C89, things may be different).  Thus, when used in different translation
units as types for one variable, that constitutes undefined behavior.
'gcc -flto' is smart enough to detect this and warn in some cases.
Luckily it doesn't act adversely upon it (yet).

The Libtool source code is dumb enough to have used all five of these
declarations (we can blissfully ignore the s/void */char */ that was
also used for pre-ANSI compilers):


Libtool 1.5.26 used (C) with
  extern const lt_dlsymlist lt_preloaded_symbols[];

in the declaration in ltdl.h, and (D) in the definition in ltmain.in,
(with s/OBJECT/lt_preloaded_symbols[] = .../).

The 1.5.26 manual documented (B) but then declared
  @deftypevar {const lt_dlsymlist *} lt_preloaded_symbols

which is just plain incompatible to the source code even in C89.

The 1.5.26 as well as master 'demo' and 'pdemo' test cases use (A) with
  extern const struct lt_symlist lt_preloaded_symbols[];

which may have been OK according to C89, but (A) doesn't match the
documentation either.

-------

Libtool master has more than one symlist (lt_preloaded_symbols is
#defined to some other string matching lt_*_LTX_preloaded_symbols).

The ltdl.h header uses (C) as declaration, with
        extern const lt_dlsymlist lt_preloaded_symbols[];

and ltmain.m4sh uses (C) as well, except that the 'const' is omitted on
systems which have trouble with relocations in const data or perform
relocations at runtime (osf5 the former, cygwin, mingw, cegcc, the
latter).  This non-const-ness is not reflected in the declaration of
lt__PROGRAM__LTX_preloaded_symbols in ltdl.h, nor that of
lt_LTDLOPEN_LTX_preloaded_symbols in ltdl.c.


In the manual, master uses (E), with
  @deftypefn {Structure} {struct} lt_dlsymlist @{ @w{const char address@hidden
+};} @w{const lt_dlsymbol @var{symbols}[];} @}

Wow, that's a plain incompatibility with (C) in any C dialect!

------


Thus far the analysis.  Question is, how do we fix it.  My preference
would be to fix the manual and the test cases, since the actual code has
been fairly stable.

Then it only remains to fix the const-ness in the declaration.  In a
followup.

OK to apply?

Thanks,
Ralf

 ChangeLog                             |    9 +++++++++
 doc/libtool.texi                      |   26 ++++++++++----------------
 tests/demo/dlmain.c                   |   11 ++++++-----
 tests/pdemo/longer_file_name_dlmain.c |   11 ++++++-----
 4 files changed, 31 insertions(+), 26 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index b324240..c082cee 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,14 @@
 2010-04-04  Ralf Wildenhues  <address@hidden>
 
+       Fix incompatible struct declarations.
+       * doc/libtool.texi (Dlpreopening): Remove broken documentation
+       of lt_dlsymbol and lt_dlsymlist.  Document typedef lt_dlsymlist
+       and symbol lt_preloaded_symbols according to the implementation.
+       * tests/demo/dlmain.c (lt_symlist): Make struct anonymous ...
+       (lt_dlsymlist): ... and typedef to this name.
+       (lt_preloaded_symbols, main): Adjust.
+       * tests/pdemo/longer_file_name_dlmain.c: Likewise.
+
        Support GCC LTO on GNU/Linux.
        * NEWS: Update.
        * libltdl/config/ltmain.m4sh (func_mode_link): Allow through
diff --git a/doc/libtool.texi b/doc/libtool.texi
index 323bf4e..f73f5a7 100644
--- a/doc/libtool.texi
+++ b/doc/libtool.texi
@@ -3388,25 +3388,15 @@ you must declare the objects you want your application 
to dlopen by
 using the @option{-dlopen} or @option{-dlpreopen} flags when you link your
 program (@pxref{Link mode}).
 
address@hidden {Structure} {struct} lt_dlsymbol @{ @w{const char 
address@hidden;} @w{void address@hidden;} @}
address@hidden {Data Type} {lt_dlsymlist} typedef struct @
+  @{ @w{const char address@hidden;} @w{void address@hidden;} @} lt_dlsymlist
 The @var{name} attribute is a null-terminated character string of the
 symbol name, such as @code{"fprintf"}.  The @var{address} attribute is a
 generic pointer to the appropriate object, such as @code{&fprintf}.
address@hidden deftypefn
-
address@hidden {Structure} {struct} lt_dlsymlist @{ @w{const char 
address@hidden;} @w{const lt_dlsymbol @var{symbols}[];} @}
-The @var{originator} attribute is a null-terminated character string,
-naming the compilation unit that @var{symbols} were preloaded on
-behalf of.  This is usually the basename of a library,
address@hidden has a corresponding @var{originator} value of
address@hidden; if the @var{symbols} are for the benefit of the
-application proper, then @var{originator} is @samp{@@PROGRAM@@},
-though Libtool takes care of that detail if you use
address@hidden
address@hidden deftypefn
address@hidden deftp
 
address@hidden {const lt_dlsymlist *} lt_preloaded_symbols
-An array of @var{lt_symbol} structures, representing all the preloaded
address@hidden {const lt_dlsymlist } lt_preloaded_symbols[]
+An array of @var{lt_dlsymlist} structures, representing all the preloaded
 symbols linked into the program proper.  For each module
 @option{-dlpreopen}ed by the Libtool linked program
 there is an element with the @var{name} of the module and an @var{address}
@@ -3414,6 +3404,10 @@ of @code{0}, followed by all symbols exported from this 
file.
 For the executable itself the special name @samp{@@PROGRAM@@} is used.
 The last element of all has a @var{name} and @var{address} of
 @code{0}.
+
+To facilitate inclusion of symbol lists into libraries,
address@hidden is @samp{#define}d to a suitably unique name
+in @file{ltdl.h}.
 @end deftypevar
 
 Some compilers may allow identifiers that are not valid in ANSI C, such
diff --git a/tests/demo/dlmain.c b/tests/demo/dlmain.c
index 0d42d88..c970998 100644
--- a/tests/demo/dlmain.c
+++ b/tests/demo/dlmain.c
@@ -1,6 +1,7 @@
 /* dlmain.c -- hello test program that uses simulated dynamic linking
 
-   Copyright (C) 1996-1999, 2004, 2006, 2007 Free Software Foundation, Inc.
+   Copyright (C) 1996-1999, 2004, 2006, 2007, 2010 Free Software
+   Foundation, Inc.
 
    This file is part of GNU Libtool.
 
@@ -27,18 +28,18 @@ or obtained by writing to the Free Software Foundation, 
Inc.,
 
 #define lt_preloaded_symbols lt__PROGRAM__LTX_preloaded_symbols
 
-struct lt_symlist
+typedef struct
 {
   const char *name;
   lt_ptr_t address;
-};
+} lt_dlsymlist;
 
-extern const struct lt_symlist lt_preloaded_symbols[];
+extern const lt_dlsymlist lt_preloaded_symbols[];
 
 int
 main ()
 {
-  const struct lt_symlist *s;
+  const lt_dlsymlist *s;
   int (*pfoo)() = 0;
   int (*phello)() = 0;
   int *pnothing = 0;
diff --git a/tests/pdemo/longer_file_name_dlmain.c 
b/tests/pdemo/longer_file_name_dlmain.c
index fdb5526..ef1e4c5 100644
--- a/tests/pdemo/longer_file_name_dlmain.c
+++ b/tests/pdemo/longer_file_name_dlmain.c
@@ -1,6 +1,7 @@
 /* dlmain.c -- hello test program that uses simulated dynamic linking
 
-   Copyright (C) 1996-1999, 2004, 2006, 2007 Free Software Foundation, Inc.
+   Copyright (C) 1996-1999, 2004, 2006, 2007, 2010 Free Software
+   Foundation, Inc.
 
    This file is part of GNU Libtool.
 
@@ -27,18 +28,18 @@ or obtained by writing to the Free Software Foundation, 
Inc.,
 
 #define lt_preloaded_symbols lt__PROGRAM__LTX_preloaded_symbols
 
-struct lt_symlist
+typedef struct
 {
   const char *name;
   lt_ptr_t address;
-};
+} lt_dlsymlist;
 
-extern const struct lt_symlist lt_preloaded_symbols[];
+extern const lt_dlsymlist lt_preloaded_symbols[];
 
 int
 main (int argc, char **argv)
 {
-  const struct lt_symlist *s;
+  const lt_dlsymlist *s;
   int (*pfoo)() = 0;
   int (*phello)() = 0;
   int *pnothing = 0;
-- 
1.7.0.rc1.161.g90487