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References: <20220929020823.1373722-1-aik@ozlabs.ru>
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From:   Masahiro Yamada <masahiroy@kernel.org>
Date:   Sat, 12 Nov 2022 05:58:20 +0900
Message-ID: <CAK7LNARv=yLgyxz6QNt+0NXNK7c0+LOPcmAa1+fHRaT7ajgGng@mail.gmail.com>
Subject: Re: [PATCH kernel v3] zstd: Fixing mixed module-builtin objects
To:     Alexey Kardashevskiy <aik@ozlabs.ru>
Cc:     linux-kernel@vger.kernel.org, Nick Terrell <terrelln@fb.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        kernel test robot <lkp@intel.com>
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On Thu, Sep 29, 2022 at 11:08 AM Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
>
> 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.


BTW, how to reproduce this error?

You referred to the arch/powerpc/Makefile,
but ARCH=powerpc cannot enable Clang LTO.
(powerpc does not select ARCH_SUPPORTS_LTO_CLANG).


> This works around the issue by introducing a zstd_common module with
> shared code.
>
> Cc: Masahiro Yamada <masahiroy@kernel.org>
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> [robot found a problem in v2]
> Reported-by: kernel test robot <lkp@intel.com>
> ---
> Changes:
> v3:
> * added EXPORT_SYMBOL_GPL to compile with:
> CONFIG_ZSTD_COMMON=m
> CONFIG_ZSTD_COMPRESS=m
> CONFIG_ZSTD_DECOMPRESS=m
> Vast majority of cases have CONFIG_ZSTD_COMMON=y so this went unnoticed
> ---
>  lib/zstd/Makefile                | 18 ++++++++----------
>  lib/zstd/common/entropy_common.c |  5 ++++-
>  lib/zstd/common/zstd_common.c    | 10 ++++++++++
>  lib/Kconfig                      |  8 ++++++--
>  4 files changed, 28 insertions(+), 13 deletions(-)
>
> diff --git a/lib/zstd/Makefile b/lib/zstd/Makefile
> index fc45339fc3a3..440bd0007ae2 100644
> --- a/lib/zstd/Makefile
> +++ b/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 \
> -               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 \
> +
> +zstd_common-y := \
> +               common/debug.o \
> +               common/entropy_common.o \
> +               common/error_private.o \
> +               common/fse_decompress.o \
> +               common/zstd_common.o \
> diff --git a/lib/zstd/common/entropy_common.c b/lib/zstd/common/entropy_common.c
> index 53b47a2b52ff..a311808c0d56 100644
> --- a/lib/zstd/common/entropy_common.c
> +++ b/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);
> diff --git a/lib/zstd/common/zstd_common.c b/lib/zstd/common/zstd_common.c
> index 3d7e35b309b5..0f1f63be25d9 100644
> --- a/lib/zstd/common/zstd_common.c
> +++ b/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");
> diff --git a/lib/Kconfig b/lib/Kconfig
> index dc1ab2ed1dc6..3ea8941ab18d 100644
> --- a/lib/Kconfig
> +++ b/lib/Kconfig
> @@ -343,12 +343,16 @@ config LZ4HC_COMPRESS
>  config LZ4_DECOMPRESS
>         tristate
>
> +config ZSTD_COMMON
> +       select XXHASH
> +       tristate
> +
>  config ZSTD_COMPRESS
> -       select XXHASH
> +       select ZSTD_COMMON
>         tristate
>
>  config ZSTD_DECOMPRESS
> -       select XXHASH
> +       select ZSTD_COMMON
>         tristate
>
>  source "lib/xz/Kconfig"
> --
> 2.37.3
>


-- 
Best Regards
Masahiro Yamada