linux-kernel - Re: [PATCH] lz4: fix KERNEL

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Date:   Wed, 8 Feb 2017 13:34:59 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Sven Schmidt <4sschmid@...ormatik.uni-hamburg.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lz4: fix KERNEL_LZ4 support

On Wed,  8 Feb 2017 22:19:23 +0100 Arnd Bergmann <arnd@...db.de> wrote:

> The updated lz4 library removed the #ifdef guards around the various
> EXPORT_SYMBOL statements in the original kernel lz4 support, which broke
> CONFIG_KERNEL_LZ4 on x86:
> 
> x86_64-linux-ld: -r and -pie may not be used together
> scripts/Makefile.build:308: recipe for target 'arch/x86/boot/compressed/misc.o' failed
> 
> This uses a simpler way to do the same thing, by overriding the
> EXPORT_SYMBOL macro.
> 

hm, why does this CONFIG_KERNEL_LZ4 thing exist?  What makes lz4
different from a billion other kernel modules?

> index 9bf918233749..a390f63bc475 100644
> --- a/lib/lz4/lz4_decompress.c
> +++ b/lib/lz4/lz4_decompress.c
> @@ -40,6 +40,11 @@
>  #include <linux/kernel.h>
>  #include <asm/unaligned.h>
>  
> +#ifdef STATIC
> +#undef EXPORT_SYMBOL
> +#define EXPORT_SYMBOL(x)
> +#endif
> +

That is a bit hacky, and somewhat "surprising".  Why not do it the old
fashioned way?

--- a/lib/lz4/lz4_decompress.c~lz4-fix-kernel_lz4-support-fix
+++ a/lib/lz4/lz4_decompress.c
@@ -328,7 +323,6 @@ int LZ4_decompress_safe(const char *sour
 		maxDecompressedSize, endOnInputSize, full, 0,
 		noDict, (BYTE *)dest, NULL, 0);
 }
-EXPORT_SYMBOL(LZ4_decompress_safe);
 
 int LZ4_decompress_safe_partial(const char *source, char *dest,
 	int compressedSize, int targetOutputSize, int maxDecompressedSize)
@@ -337,7 +331,6 @@ int LZ4_decompress_safe_partial(const ch
 		maxDecompressedSize, endOnInputSize, partial,
 		targetOutputSize, noDict, (BYTE *)dest, NULL, 0);
 }
-EXPORT_SYMBOL(LZ4_decompress_safe_partial);
 
 int LZ4_decompress_fast(const char *source, char *dest, int originalSize)
 {
@@ -345,7 +338,6 @@ int LZ4_decompress_fast(const char *sour
 		endOnOutputSize, full, 0, withPrefix64k,
 		(BYTE *)(dest - 64 * KB), NULL, 64 * KB);
 }
-EXPORT_SYMBOL(LZ4_decompress_fast);
 
 int LZ4_setStreamDecode(LZ4_streamDecode_t *LZ4_streamDecode,
 	const char *dictionary, int dictSize)
@@ -358,7 +350,6 @@ int LZ4_setStreamDecode(LZ4_streamDecode
 	lz4sd->extDictSize	= 0;
 	return 1;
 }
-EXPORT_SYMBOL(LZ4_setStreamDecode);
 
 /*
  * *_continue() :
@@ -406,7 +397,6 @@ int LZ4_decompress_safe_continue(LZ4_str
 
 	return result;
 }
-EXPORT_SYMBOL(LZ4_decompress_safe_continue);
 
 int LZ4_decompress_fast_continue(LZ4_streamDecode_t *LZ4_streamDecode,
 	const char *source, char *dest, int originalSize)
@@ -441,7 +431,6 @@ int LZ4_decompress_fast_continue(LZ4_str
 
 	return result;
 }
-EXPORT_SYMBOL(LZ4_decompress_fast_continue);
 
 /*
  * Advanced decoding functions :
@@ -478,7 +467,6 @@ int LZ4_decompress_safe_usingDict(const
 	return LZ4_decompress_usingDict_generic(source, dest,
 		compressedSize, maxOutputSize, 1, dictStart, dictSize);
 }
-EXPORT_SYMBOL(LZ4_decompress_safe_usingDict);
 
 int LZ4_decompress_fast_usingDict(const char *source, char *dest,
 	int originalSize, const char *dictStart, int dictSize)
@@ -486,7 +474,17 @@ int LZ4_decompress_fast_usingDict(const
 	return LZ4_decompress_usingDict_generic(source, dest, 0,
 		originalSize, 0, dictStart, dictSize);
 }
+
+#ifndef STATIC
+EXPORT_SYMBOL(LZ4_decompress_safe);
+EXPORT_SYMBOL(LZ4_decompress_safe_partial);
+EXPORT_SYMBOL(LZ4_decompress_fast);
+EXPORT_SYMBOL(LZ4_setStreamDecode);
+EXPORT_SYMBOL(LZ4_decompress_safe_continue);
+EXPORT_SYMBOL(LZ4_decompress_fast_continue);
+EXPORT_SYMBOL(LZ4_decompress_safe_usingDict);
 EXPORT_SYMBOL(LZ4_decompress_fast_usingDict);
+#endif
 
 MODULE_LICENSE("Dual BSD/GPL");
 MODULE_DESCRIPTION("LZ4 decompressor");
_