Hi Paul, FYI, the error/warning still remains. tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master head: a96bfed64c8986d6404e553f18203cae1f5ac7e6 commit: a510b616131f85215ba156ed67e5ed1c0701f80f MIPS: Add support for ZSTD-compressed kernels date: 10 months ago config: mips-randconfig-r036-20210622 (attached as .config) compiler: mips-linux-gcc (GCC) 9.3.0 reproduce (this is a W=1 build): wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross chmod +x ~/bin/make.cross # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit... git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git git fetch --no-tags linus master git checkout a510b616131f85215ba156ed67e5ed1c0701f80f # save the attached .config to linux build tree COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=mips If you fix the issue, kindly add following tag as appropriate Reported-by: kernel test robot <lkp(a)intel.com&gt; All warnings (new ones prefixed by >>): arch/mips/boot/compressed/decompress.c:38:6: warning: no previous prototype for 'error' [-Wmissing-prototypes] 38 | void error(char *x) | ^~~~~ In file included from arch/mips/boot/compressed/../../../../lib/decompress_unzstd.c:75, from arch/mips/boot/compressed/decompress.c:76: 126 | ZSTD_DCtx *ZSTD_createDCtx_advanced(ZSTD_customMem customMem) | ^~~~~~~~~~~~~~~~~~~~~~~~ 394 | size_t ZSTD_getcBlockSize(const void *src, size_t srcSize, blockProperties_t *bpPtr) | ^~~~~~~~~~~~~~~~~~ 432 | size_t ZSTD_decodeLiteralsBlock(ZSTD_DCtx *dctx, const void *src, size_t srcSize) /* note : srcSize < BLOCKSIZE */ | ^~~~~~~~~~~~~~~~~~~~~~~~ 794 | size_t ZSTD_decodeSeqHeaders(ZSTD_DCtx *dctx, int *nbSeqPtr, const void *src, size_t srcSize) | ^~~~~~~~~~~~~~~~~~~~~ 1497 | size_t ZSTD_generateNxBytes(void *dst, size_t dstCapacity, BYTE byte, size_t length) | ^~~~~~~~~~~~~~~~~~~~ arch/mips/boot/compressed/decompress.c:81:6: warning: no previous prototype for '__stack_chk_fail' [-Wmissing-prototypes] 81 | void __stack_chk_fail(void) | ^~~~~~~~~~~~~~~~ arch/mips/boot/compressed/decompress.c:86:6: warning: no previous prototype for 'decompress_kernel' [-Wmissing-prototypes] 86 | void decompress_kernel(unsigned long boot_heap_start) | ^~~~~~~~~~~~~~~~~ In file included from arch/mips/boot/compressed/../../../../lib/zstd/fse_decompress.c:50, from arch/mips/boot/compressed/../../../../lib/decompress_unzstd.c:72, from arch/mips/boot/compressed/decompress.c:76: arch/mips/boot/compressed/../../../../lib/zstd/zstd_internal.h:124:18: warning: 'OF_defaultNormLog' defined but not used [-Wunused-const-variable=] 124 | static const U32 OF_defaultNormLog = OF_DEFAULTNORMLOG; | ^~~~~~~~~~~~~~~~~ arch/mips/boot/compressed/../../../../lib/zstd/zstd_internal.h:122:18: warning: 'OF_defaultNorm' defined but not used [-Wunused-const-variable=] 122 | static const S16 OF_defaultNorm[MaxOff + 1] = {1, 1, 1, 1, 1, 1, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, -1, -1, -1, -1, -1}; | ^~~~~~~~~~~~~~ arch/mips/boot/compressed/../../../../lib/zstd/zstd_internal.h:120:18: warning: 'ML_defaultNormLog' defined but not used [-Wunused-const-variable=] 120 | static const U32 ML_defaultNormLog = ML_DEFAULTNORMLOG; | ^~~~~~~~~~~~~~~~~ arch/mips/boot/compressed/../../../../lib/zstd/zstd_internal.h:117:18: warning: 'ML_defaultNorm' defined but not used [-Wunused-const-variable=] 117 | static const S16 ML_defaultNorm[MaxML + 1] = {1, 4, 3, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, | ^~~~~~~~~~~~~~ arch/mips/boot/compressed/../../../../lib/zstd/zstd_internal.h:113:18: warning: 'LL_defaultNormLog' defined but not used [-Wunused-const-variable=] 113 | static const U32 LL_defaultNormLog = LL_DEFAULTNORMLOG; | ^~~~~~~~~~~~~~~~~ arch/mips/boot/compressed/../../../../lib/zstd/zstd_internal.h:111:18: warning: 'LL_defaultNorm' defined but not used [-Wunused-const-variable=] 111 | static const S16 LL_defaultNorm[MaxLL + 1] = {4, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 1, 1, 1, 1, 1, -1, -1, -1, -1}; | ^~~~~~~~~~~~~~ vim +/ZSTD_createDCtx_advanced +126 arch/mips/boot/compressed/../../../../lib/zstd/decompress.c 73f3d1b48f5069 Nick Terrell 2017-08-09 125 73f3d1b48f5069 Nick Terrell 2017-08-09 @126 ZSTD_DCtx *ZSTD_createDCtx_advanced(ZSTD_customMem customMem) 73f3d1b48f5069 Nick Terrell 2017-08-09 127 { 73f3d1b48f5069 Nick Terrell 2017-08-09 128 ZSTD_DCtx *dctx; 73f3d1b48f5069 Nick Terrell 2017-08-09 129 73f3d1b48f5069 Nick Terrell 2017-08-09 130 if (!customMem.customAlloc || !customMem.customFree) 73f3d1b48f5069 Nick Terrell 2017-08-09 131 return NULL; 73f3d1b48f5069 Nick Terrell 2017-08-09 132 73f3d1b48f5069 Nick Terrell 2017-08-09 133 dctx = (ZSTD_DCtx *)ZSTD_malloc(sizeof(ZSTD_DCtx), customMem); 73f3d1b48f5069 Nick Terrell 2017-08-09 134 if (!dctx) 73f3d1b48f5069 Nick Terrell 2017-08-09 135 return NULL; 73f3d1b48f5069 Nick Terrell 2017-08-09 136 memcpy(&dctx->customMem, &customMem, sizeof(customMem)); 73f3d1b48f5069 Nick Terrell 2017-08-09 137 ZSTD_decompressBegin(dctx); 73f3d1b48f5069 Nick Terrell 2017-08-09 138 return dctx; 73f3d1b48f5069 Nick Terrell 2017-08-09 139 } 73f3d1b48f5069 Nick Terrell 2017-08-09 140 :::::: The code at line 126 was first introduced by commit :::::: 73f3d1b48f5069d46ba48aa28c2898dc93185560 lib: Add zstd modules :::::: TO: Nick Terrell <terrelln(a)fb.com&gt; :::::: CC: Chris Mason <clm(a)fb.com&gt; --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org