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From: Fedin Pavel <p DOT fedin AT samsung DOT com>
To: "'Andrew Schulman'" <schulman DOT andrew AT epamail DOT epa DOT gov>, cygwin AT cygwin DOT com
References: <000001ce7e08$2b866830$82933890$%fedin AT samsung DOT com> <u4ett8due4p6h9ku1iumscvulp0g688tgk AT 4ax DOT com> <4q4ut8had25hqmo8b0752i8asuv6ism2qh AT 4ax DOT com> <002901ce7f0a$9da99420$d8fcbc60$%fedin AT samsung DOT com> <tq50u89pa1s7us0cff5rnu8k5ocumac510 AT 4ax DOT com>
In-reply-to: <tq50u89pa1s7us0cff5rnu8k5ocumac510@4ax.com>
Subject: [PATCH] Fix optional variables in libargp
Date: Wed, 17 Jul 2013 10:32:18 +0400
Message-id: <002601ce82b7$63229580$2967c080$%fedin@samsung.com>
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 Hello!

> Okay, well I agree that this sounds like a good solution.  For now you
> have a workaround, and I'll be glad to consider a patch if you submit
> one.

 Please take it. This is my experimental implementation which appears to be
simpler than i suggested.

 Some details: this implementation adds explicit dllexport attribute to
these 4 variables. This allows to look them up using GetProcAddress(). The
dllexport attribute has to be added explicitly because when compiling an
.exe file (without -shared switch) gcc does not mark externals as exportable
by default. When building a .dll, all external symbols are marked as
exportable by default, *UNLESS* we have at least one explicit dllexport
specification, hence i surrounded this with #ifndef DLL_EXPORT, this
definition is introduced by libtool when building a shared library.
 This implementation would not work in the following corner cases:
 a) .exe file uses some foo.dll library, which defines these variables and
uses libargp - symbols are picked up only from .exe file itself.
 b) Building that foo.dll manually without DLL_EXPORT definition can get
broken - the compiler will see dllexport attribute, and it will override the
default behavior to make all externs exportable.
 I believe these cases are quite unusual so it's OK. Getting rid of these
limitations would need more complex implementation with more changes.

 I have tested the implementation on x86-64 with RedHat's Prelink utility,
and it works quite fine. i386 should work too, but please retest, just in
case.

 Additionally, i added the second #ifdef _WIN32 in order to make the same
thing working also for MinGW target.

Kind regards,
Pavel Fedin
Expert Engineer
Samsung Electronics Research center Russia

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	name="libargp-20110921-fix-optional-variables.diff"
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	filename="libargp-20110921-fix-optional-variables.diff"

diff -ru src/libargp-20110921.orig/gllib/argp.h src/libargp-20110921/gllib/=
argp.h=0A=
--- src/libargp-20110921.orig/gllib/argp.h	2011-09-23 03:31:26.000000000 +0=
500=0A=
+++ src/libargp-20110921/gllib/argp.h	2013-07-15 12:03:51.616647900 +0500=
=0A=
@@ -64,6 +64,18 @@=0A=
 typedef int error_t;=0A=
 # define __error_t_defined=0A=
 #endif=0A=
+=0A=
+#ifndef DLL_EXPORT=0A=
+#ifdef __CYGWIN__=0A=
+#define __dllexport __declspec(dllexport)=0A=
+#endif=0A=
+#ifdef _WIN32=0A=
+#define __dllexport __declspec(dllexport)=0A=
+#endif=0A=
+#endif=0A=
+#ifndef __dllexport=0A=
+#define __dllexport=0A=
+#endif=0A=
 =0C=0A=
 #ifdef  __cplusplus=0A=
 extern "C" {=0A=
@@ -441,14 +453,14 @@=0A=
    option --version is added (unless the ARGP_NO_HELP flag is used), which=
=0A=
    will print this string followed by a newline and exit (unless the=0A=
    ARGP_NO_EXIT flag is used).  Overridden by ARGP_PROGRAM_VERSION_HOOK.  =
*/=0A=
-extern const char *argp_program_version;=0A=
+__dllexport extern const char *argp_program_version;=0A=
=20=0A=
 /* If defined or set by the user program to a non-zero value, then a defau=
lt=0A=
    option --version is added (unless the ARGP_NO_HELP flag is used), which=
=0A=
    calls this function with a stream to print the version to and a pointer=
 to=0A=
    the current parsing state, and then exits (unless the ARGP_NO_EXIT flag=
 is=0A=
    used).  This variable takes precedent over ARGP_PROGRAM_VERSION.  */=0A=
-extern void (*argp_program_version_hook) (FILE *__restrict __stream,=0A=
+__dllexport extern void (*argp_program_version_hook) (FILE *__restrict __s=
tream,=0A=
                                           struct argp_state *__restrict=0A=
                                           __state);=0A=
=20=0A=
@@ -457,12 +469,12 @@=0A=
    argp_help if the ARGP_HELP_BUG_ADDR flag is set (as it is by various=0A=
    standard help messages), embedded in a sentence that says something like=
=0A=
    `Report bugs to ADDR.'.  */=0A=
-extern const char *argp_program_bug_address;=0A=
+__dllexport extern const char *argp_program_bug_address;=0A=
=20=0A=
 /* The exit status that argp will use when exiting due to a parsing error.=
=0A=
    If not defined or set by the user program, this defaults to EX_USAGE fr=
om=0A=
    <sysexits.h>.  */=0A=
-extern error_t argp_err_exit_status;=0A=
+__dllexport extern error_t argp_err_exit_status;=0A=
 =0C=0A=
 /* Flags for argp_help.  */=0A=
 #define ARGP_HELP_USAGE         0x01 /* a Usage: message. */=0A=
diff -ru src/libargp-20110921.orig/gllib/argp-parse.c src/libargp-20110921/=
gllib/argp-parse.c=0A=
--- src/libargp-20110921.orig/gllib/argp-parse.c	2011-09-23 03:31:26.000000=
000 +0500=0A=
+++ src/libargp-20110921/gllib/argp-parse.c	2013-07-15 11:39:49.690236100 +=
0500=0A=
@@ -64,6 +64,42 @@=0A=
 /* EZ alias for ARGP_ERR_UNKNOWN.  */=0A=
 #define EBADKEY ARGP_ERR_UNKNOWN=0A=
 =0C=0A=
+/* Windows does not support things like weak symbols, neither it will merg=
e two=0A=
+   external symbols. In order to make our optional variables working, we h=
ave=0A=
+   to do this trick. What we do here is looking up respective variables in=
=0A=
+   main .exe file and patching our versions with correct pointers=0A=
+   Note that the whole thing relies on these variables being declared with=
=0A=
+   __declspec(dllexport). */=0A=
+#ifdef DLL_EXPORT=0A=
+=0A=
+#include <windows.h>=0A=
+=0A=
+#ifdef __i386__=0A=
+#define PREFIX "_"=0A=
+#else=0A=
+#define PREFIX=0A=
+#endif=0A=
+=0A=
+#define PatchPtr(var)					\=0A=
+  p =3D (void **)GetProcAddress(NULL, PREFIX #var );	\=0A=
+  if (p) var =3D *p;=0A=
+=0A=
+#define PatchInt(var)					\=0A=
+  i =3D (int *)GetProcAddress(NULL, PREFIX #var );	\=0A=
+  if (i) var =3D *i;=0A=
+=0A=
+static void __attribute__((constructor)) patch_vars(void)=0A=
+{=0A=
+  void **p;=0A=
+  int *i;=0A=
+=0A=
+  PatchPtr(argp_program_version);=0A=
+  PatchPtr(argp_program_version_hook);=0A=
+  PatchPtr(argp_program_bug_address);=0A=
+  PatchInt(argp_err_exit_status);=0A=
+}=0A=
+#endif=0A=
+=0A=
 /* Default options.  */=0A=
=20=0A=
 /* When argp is given the --HANG switch, _ARGP_HANG is set and argp will s=
leep=0A=


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