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Message-ID: <d4ebca66-2899-7cd1-3cb1-4b1a587eb2bf@ozlabs.ru>
Date:   Wed, 11 May 2022 12:03:31 +1000
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Subject: Re: [PATCH kernel v2] zstd: Fixing mixed module-builtin objects
Content-Language: en-US
To:     linux-kernel@vger.kernel.org
Cc:     Nick Terrell <terrelln@fb.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Masahiro Yamada <masahiroy@kernel.org>
References: <20220429053329.2278740-1-aik@ozlabs.ru>
From:   Alexey Kardashevskiy <aik@ozlabs.ru>
In-Reply-To: <20220429053329.2278740-1-aik@ozlabs.ru>
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On 4/29/22 15:33, Alexey Kardashevskiy 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.
> 
> 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>


Ping? Thanks,


> ---
> Changes:
> v2:
> * add a new module instead of inlining common bits
> 
> ---
>   lib/zstd/Makefile                | 18 ++++++++----------
>   lib/zstd/common/entropy_common.c |  4 +++-
>   lib/zstd/common/zstd_common.c    |  7 +++++++
>   lib/Kconfig                      |  8 ++++++--
>   4 files changed, 24 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..f84612627471 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,
> diff --git a/lib/zstd/common/zstd_common.c b/lib/zstd/common/zstd_common.c
> index 3d7e35b309b5..06f62b2026d5 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"
> @@ -59,6 +60,7 @@ 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 +73,7 @@ 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 +84,7 @@ 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 087e06b4cdfd..33f3a7054cdd 100644
> --- a/lib/Kconfig
> +++ b/lib/Kconfig
> @@ -333,12 +333,16 @@ 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"