zstd: Fixing mixed module-builtin objects

With CONFIG_ZSTD_COMPRESS=m and CONFIG_ZSTD_DECOMPRESS=y we end up in
a situation when files from lib/zstd/common/ are compiled once to be
linked later for ZSTD_DECOMPRESS (build-in) and ZSTD_COMPRESS (module)
even though CFLAGS are different for builtins and modules.
So far somehow this was not a problem but enabling LLVM LTO exposes
the problem as:

ld.lld: error: linking module flags 'Code Model': IDs have conflicting values in 'lib/built-in.a(zstd_common.o at 5868)' and 'ld-temp.o'

This particular conflict is caused by KBUILD_CFLAGS=-mcmodel=medium vs.
KBUILD_CFLAGS_MODULE=-mcmodel=large , modules use the large model on
POWERPC as explained at
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/powerpc/Makefile?h=v5.18-rc4#n127
but the current use of common files is wrong anyway.

This works around the issue by introducing a zstd_common module with
shared code.
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

lib/Kconfig

@@ -343,12 +343,16 @@ config LZ4HC_COMPRESS
 config LZ4_DECOMPRESS
 	tristate
 
-config ZSTD_COMPRESS
+config ZSTD_COMMON
 	select XXHASH
 	tristate
 
+config ZSTD_COMPRESS
+	select ZSTD_COMMON
+	tristate
+
 config ZSTD_DECOMPRESS
-	select XXHASH
+	select ZSTD_COMMON
 	tristate
 
 source "lib/xz/Kconfig"

lib/zstd/Makefile

@@ -10,14 +10,10 @@
 # ################################################################
 obj-$(CONFIG_ZSTD_COMPRESS) += zstd_compress.o
 obj-$(CONFIG_ZSTD_DECOMPRESS) += zstd_decompress.o
+obj-$(CONFIG_ZSTD_COMMON) += zstd_common.o
 
 zstd_compress-y := \
 		zstd_compress_module.o \
-		common/debug.o \
-		common/entropy_common.o \
-		common/error_private.o \
-		common/fse_decompress.o \
-		common/zstd_common.o \
 		compress/fse_compress.o \
 		compress/hist.o \
 		compress/huf_compress.o \
@@ -33,12 +29,14 @@ zstd_compress-y := \
 
 zstd_decompress-y := \
 		zstd_decompress_module.o \
+		decompress/huf_decompress.o \
+		decompress/zstd_ddict.o \
+		decompress/zstd_decompress.o \
+		decompress/zstd_decompress_block.o \
+
+zstd_common-y := \
 		common/debug.o \
 		common/entropy_common.o \
 		common/error_private.o \
 		common/fse_decompress.o \
 		common/zstd_common.o \
-		decompress/huf_decompress.o \
-		decompress/zstd_ddict.o \
-		decompress/zstd_decompress.o \
-		decompress/zstd_decompress_block.o \

lib/zstd/common/entropy_common.c

@@ -15,6 +15,7 @@
 /* *************************************
 *  Dependencies
 ***************************************/
+#include <linux/module.h>
 #include "mem.h"
 #include "error_private.h"       /* ERR_*, ERROR */
 #define FSE_STATIC_LINKING_ONLY  /* FSE_MIN_TABLELOG */
@@ -239,7 +240,7 @@ size_t FSE_readNCount(
 {
     return FSE_readNCount_bmi2(normalizedCounter, maxSVPtr, tableLogPtr, headerBuffer, hbSize, /* bmi2 */ 0);
 }
-
+EXPORT_SYMBOL_GPL(FSE_readNCount);
 
 /*! HUF_readStats() :
     Read compact Huffman tree, saved by HUF_writeCTable().
@@ -255,6 +256,7 @@ size_t HUF_readStats(BYTE* huffWeight, size_t hwSize, U32* rankStats,
     U32 wksp[HUF_READ_STATS_WORKSPACE_SIZE_U32];
     return HUF_readStats_wksp(huffWeight, hwSize, rankStats, nbSymbolsPtr, tableLogPtr, src, srcSize, wksp, sizeof(wksp), /* bmi2 */ 0);
 }
+EXPORT_SYMBOL_GPL(HUF_readStats);
 
 FORCE_INLINE_TEMPLATE size_t
 HUF_readStats_body(BYTE* huffWeight, size_t hwSize, U32* rankStats,
@@ -355,3 +357,4 @@ size_t HUF_readStats_wksp(BYTE* huffWeight, size_t hwSize, U32* rankStats,
     (void)bmi2;
     return HUF_readStats_body_default(huffWeight, hwSize, rankStats, nbSymbolsPtr, tableLogPtr, src, srcSize, workSpace, wkspSize);
 }
+EXPORT_SYMBOL_GPL(HUF_readStats_wksp);

lib/zstd/common/zstd_common.c

@@ -13,6 +13,7 @@
 /*-*************************************
 *  Dependencies
 ***************************************/
+#include <linux/module.h>
 #define ZSTD_DEPS_NEED_MALLOC
 #include "zstd_deps.h"   /* ZSTD_malloc, ZSTD_calloc, ZSTD_free, ZSTD_memset */
 #include "error_private.h"
@@ -35,14 +36,17 @@ const char* ZSTD_versionString(void) { return ZSTD_VERSION_STRING; }
  *  tells if a return value is an error code
  *  symbol is required for external callers */
 unsigned ZSTD_isError(size_t code) { return ERR_isError(code); }
+EXPORT_SYMBOL_GPL(ZSTD_isError);
 
 /*! ZSTD_getErrorName() :
  *  provides error code string from function result (useful for debugging) */
 const char* ZSTD_getErrorName(size_t code) { return ERR_getErrorName(code); }
+EXPORT_SYMBOL_GPL(ZSTD_getErrorName);
 
 /*! ZSTD_getError() :
  *  convert a `size_t` function result into a proper ZSTD_errorCode enum */
 ZSTD_ErrorCode ZSTD_getErrorCode(size_t code) { return ERR_getErrorCode(code); }
+EXPORT_SYMBOL_GPL(ZSTD_getErrorCode);
 
 /*! ZSTD_getErrorString() :
  *  provides error code string from enum */
@@ -59,6 +63,7 @@ void* ZSTD_customMalloc(size_t size, ZSTD_customMem customMem)
         return customMem.customAlloc(customMem.opaque, size);
     return ZSTD_malloc(size);
 }
+EXPORT_SYMBOL_GPL(ZSTD_customMalloc);
 
 void* ZSTD_customCalloc(size_t size, ZSTD_customMem customMem)
 {
@@ -71,6 +76,7 @@ void* ZSTD_customCalloc(size_t size, ZSTD_customMem customMem)
     }
     return ZSTD_calloc(1, size);
 }
+EXPORT_SYMBOL_GPL(ZSTD_customCalloc);
 
 void ZSTD_customFree(void* ptr, ZSTD_customMem customMem)
 {
@@ -81,3 +87,7 @@ void ZSTD_customFree(void* ptr, ZSTD_customMem customMem)
             ZSTD_free(ptr);
     }
 }
+EXPORT_SYMBOL_GPL(ZSTD_customFree);
+
+MODULE_LICENSE("Dual BSD/GPL");
+MODULE_DESCRIPTION("Zstd Common");