From: "Ronald S. Bultje" <[email protected]>
This requires the makedef perl script by Derek, from the c89-to-c99
repo. That scripts produces a .def file, listing the symbols to be
exported, based on the gcc version scripts and the built object files.
To properly load non-function symbols from DLL files, the data
symbol declarations need to have the attribute __declspec(dllimport)
when building the calling code. (On mingw, the linker can fix this
up automatically, which is why it has not been an issue so far.)
The __declspec(dllimport) attribute is added via a macro. Since
it has to be present when building code that refers to these symbols,
but not be present while building the library that exports the symbols
themselves, the Makefile is modified to add a define like
COMPILING_<libname> while building each library. This is used in the
definition of the <lib>_exportdata macro - on non-MSVC compilers, it is
empty. On MSVC, it is __declspec(dllimport) for declarations in other
libraries than the object file currently compiled.
This also implies that code that is built to link to a certain
library as a DLL can't link to the same library as a static library.
Therefore, we only allow building either static or shared but not
both at the same time. (That is, static libraries as such can be,
and actually are, built - this is used for linking the test tools to
internal symbols in the libraries - but e.g. libavformat object files
built to link to libavcodec as a DLL cannot link statically to
libavcodec.)
Also, linking to DLLs is slightly different from linking to shared
libraries on other platforms. DLLs use a thing called import
libraries, which is basically a stub library allowing the linker
to know which symbols exist in the DLL and what name the DLL will
have at runtime.
In mingw/gcc, the import library is usually named libfoo.dll.a,
which goes next to a static library named libfoo.a. This allows gcc
to pick the dynamic one, if available, from the normal -lfoo switches,
just as it does for libfoo.a vs libfoo.so on Unix. On MSVC however,
you need to literally specify the name of the import library instead of
the static library.
---
configure | 17 +++++++++++++++++
libavcodec/ac3tab.h | 3 ++-
libavcodec/dca.h | 3 ++-
libavcodec/internal.h | 7 +++++++
libavcodec/mjpeg.h | 15 ++++++++-------
libavcodec/mpeg12data.h | 3 ++-
libavcodec/mpeg4audio.h | 3 ++-
libavcodec/mpegaudiodata.h | 6 ++++--
library.mak | 1 +
9 files changed, 45 insertions(+), 13 deletions(-)
diff --git a/configure b/configure
index b30d69b..b70b1ec 100755
--- a/configure
+++ b/configure
@@ -2794,6 +2794,20 @@ case $target_os in
add_cppflags -U__STRICT_ANSI__
;;
win32|win64)
+ # Link to the import library instead of the normal static library for
+ # shared libs.
+ enabled shared && LD_LIB='%.lib'
+ shlibdir_default="$bindir_default"
+ SLIBPREF=""
+ SLIBSUF=".dll"
+ SLIBNAME_WITH_VERSION='$(SLIBPREF)$(FULLNAME)-$(LIBVERSION)$(SLIBSUF)'
+ SLIBNAME_WITH_MAJOR='$(SLIBPREF)$(FULLNAME)-$(LIBMAJOR)$(SLIBSUF)'
+ SLIB_CREATE_DEF_CMD='makedef $(SUBDIR)lib$(NAME).ver $(OBJS) >
$$(@:$(SLIBSUF)=.def)'
+ SLIB_INSTALL_NAME='$(SLIBNAME_WITH_MAJOR)'
+ SLIB_INSTALL_LINKS=
+ SLIB_INSTALL_EXTRA_SHLIB='$(SLIBNAME:$(SLIBSUF)=.lib)'
+ SLIB_INSTALL_EXTRA_LIB='$(SLIBNAME_WITH_MAJOR:$(SLIBSUF)=.def)'
+ SHFLAGS='-dll -def:$$(@:$(SLIBSUF)=.def)
-implib:$(SUBDIR)$(SLIBNAME:$(SLIBSUF)=.lib)'
objformat="win32"
ranlib=:
enable dos_paths
@@ -2930,6 +2944,9 @@ build the shared libraries as well. To only build the
shared libraries specify
EOF
exit 1;
fi
+if enabled_all msvc static shared; then
+ die "Cannot build shared and static libraries at the same time with MSVC."
+fi
die_license_disabled() {
enabled $1 || { enabled $2 && die "$2 is $1 and --enable-$1 is not
specified."; }
diff --git a/libavcodec/ac3tab.h b/libavcodec/ac3tab.h
index 8ed5052..5e11e58 100644
--- a/libavcodec/ac3tab.h
+++ b/libavcodec/ac3tab.h
@@ -24,6 +24,7 @@
#include "libavutil/common.h"
#include "ac3.h"
+#include "internal.h"
#if CONFIG_HARDCODED_TABLES
# define HCONST const
@@ -33,7 +34,7 @@
extern const uint16_t ff_ac3_frame_size_tab[38][3];
extern const uint8_t ff_ac3_channels_tab[8];
-extern const uint16_t avpriv_ac3_channel_layout_tab[8];
+extern avcodec_exportdata const uint16_t avpriv_ac3_channel_layout_tab[8];
extern const uint8_t ff_ac3_enc_channel_map[8][2][6];
extern const uint8_t ff_ac3_dec_channel_map[8][2][6];
extern const uint16_t ff_ac3_sample_rate_tab[3];
diff --git a/libavcodec/dca.h b/libavcodec/dca.h
index 1515270..ec2ffea 100644
--- a/libavcodec/dca.h
+++ b/libavcodec/dca.h
@@ -26,6 +26,7 @@
#define AVCODEC_DCA_H
#include <stdint.h>
+#include "internal.h"
/** DCA syncwords, also used for bitstream type detection */
#define DCA_MARKER_RAW_BE 0x7FFE8001
@@ -36,6 +37,6 @@
/** DCA-HD specific block starts with this marker. */
#define DCA_HD_MARKER 0x64582025
-extern const uint32_t avpriv_dca_sample_rates[16];
+extern avcodec_exportdata const uint32_t avpriv_dca_sample_rates[16];
#endif /* AVCODEC_DCA_H */
diff --git a/libavcodec/internal.h b/libavcodec/internal.h
index e5b1958..a019009 100644
--- a/libavcodec/internal.h
+++ b/libavcodec/internal.h
@@ -29,6 +29,13 @@
#include "libavutil/mathematics.h"
#include "libavutil/pixfmt.h"
#include "avcodec.h"
+#include "config.h"
+
+#if CONFIG_SHARED && defined(_WIN32) && !defined(COMPILING_avcodec)
+#define avcodec_exportdata __declspec(dllimport)
+#else
+#define avcodec_exportdata
+#endif
typedef struct InternalBuffer {
uint8_t *base[AV_NUM_DATA_POINTERS];
diff --git a/libavcodec/mjpeg.h b/libavcodec/mjpeg.h
index 1374ab3..134c178 100644
--- a/libavcodec/mjpeg.h
+++ b/libavcodec/mjpeg.h
@@ -35,6 +35,7 @@
#include "avcodec.h"
#include "put_bits.h"
+#include "internal.h"
/* JPEG marker codes */
@@ -137,16 +138,16 @@ static inline void put_marker(PutBitContext *p, int code)
case 7: ret= (left + top)>>1; break;\
}
-extern const uint8_t avpriv_mjpeg_bits_dc_luminance[];
-extern const uint8_t avpriv_mjpeg_val_dc[];
+extern avcodec_exportdata const uint8_t avpriv_mjpeg_bits_dc_luminance[];
+extern avcodec_exportdata const uint8_t avpriv_mjpeg_val_dc[];
-extern const uint8_t avpriv_mjpeg_bits_dc_chrominance[];
+extern avcodec_exportdata const uint8_t avpriv_mjpeg_bits_dc_chrominance[];
-extern const uint8_t avpriv_mjpeg_bits_ac_luminance[];
-extern const uint8_t avpriv_mjpeg_val_ac_luminance[];
+extern avcodec_exportdata const uint8_t avpriv_mjpeg_bits_ac_luminance[];
+extern avcodec_exportdata const uint8_t avpriv_mjpeg_val_ac_luminance[];
-extern const uint8_t avpriv_mjpeg_bits_ac_chrominance[];
-extern const uint8_t avpriv_mjpeg_val_ac_chrominance[];
+extern avcodec_exportdata const uint8_t avpriv_mjpeg_bits_ac_chrominance[];
+extern avcodec_exportdata const uint8_t avpriv_mjpeg_val_ac_chrominance[];
void ff_mjpeg_build_huffman_codes(uint8_t *huff_size, uint16_t *huff_code,
const uint8_t *bits_table,
diff --git a/libavcodec/mpeg12data.h b/libavcodec/mpeg12data.h
index 86ba3ec..20c3155 100644
--- a/libavcodec/mpeg12data.h
+++ b/libavcodec/mpeg12data.h
@@ -31,6 +31,7 @@
#include <stdint.h>
#include "libavutil/rational.h"
#include "rl.h"
+#include "internal.h"
extern const uint16_t ff_mpeg1_default_intra_matrix[64];
extern const uint16_t ff_mpeg1_default_non_intra_matrix[64];
@@ -48,7 +49,7 @@ extern const uint8_t ff_mpeg12_mbPatTable[64][2];
extern const uint8_t ff_mpeg12_mbMotionVectorTable[17][2];
-extern const AVRational avpriv_frame_rate_tab[];
+extern avcodec_exportdata const AVRational avpriv_frame_rate_tab[];
extern const float ff_mpeg1_aspect[16];
extern const AVRational ff_mpeg2_aspect[16];
diff --git a/libavcodec/mpeg4audio.h b/libavcodec/mpeg4audio.h
index 1ee2d7e..4109b94 100644
--- a/libavcodec/mpeg4audio.h
+++ b/libavcodec/mpeg4audio.h
@@ -25,6 +25,7 @@
#include <stdint.h>
#include "get_bits.h"
#include "put_bits.h"
+#include "internal.h"
typedef struct MPEG4AudioConfig {
int object_type;
@@ -40,7 +41,7 @@ typedef struct MPEG4AudioConfig {
int ps; ///< -1 implicit, 1 presence
} MPEG4AudioConfig;
-extern const int avpriv_mpeg4audio_sample_rates[16];
+extern avcodec_exportdata const int avpriv_mpeg4audio_sample_rates[16];
extern const uint8_t ff_mpeg4audio_channels[8];
/**
diff --git a/libavcodec/mpegaudiodata.h b/libavcodec/mpegaudiodata.h
index d1a8841..3f6622b 100644
--- a/libavcodec/mpegaudiodata.h
+++ b/libavcodec/mpegaudiodata.h
@@ -29,11 +29,13 @@
#include <stdint.h>
+#include "internal.h"
+
#define MODE_EXT_MS_STEREO 2
#define MODE_EXT_I_STEREO 1
-extern const uint16_t avpriv_mpa_bitrate_tab[2][3][15];
-extern const uint16_t avpriv_mpa_freq_tab[3];
+extern avcodec_exportdata const uint16_t avpriv_mpa_bitrate_tab[2][3][15];
+extern avcodec_exportdata const uint16_t avpriv_mpa_freq_tab[3];
extern const int ff_mpa_sblimit_table[5];
extern const int ff_mpa_quant_steps[17];
extern const int ff_mpa_quant_bits[17];
diff --git a/library.mak b/library.mak
index b365935..56a4586 100644
--- a/library.mak
+++ b/library.mak
@@ -33,6 +33,7 @@ install-libs-$(CONFIG_STATIC): install-lib$(NAME)-static
install-libs-$(CONFIG_SHARED): install-lib$(NAME)-shared
define RULES
+$(OBJS): CPPFLAGS += -DCOMPILING_$(NAME)=1
$(EXAMPLES) $(TOOLS): THISLIB = $(FULLNAME:%=$(LD_LIB))
$(TESTPROGS): THISLIB = $(SUBDIR)$(LIBNAME)
--
1.7.9.5
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