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dmarc=none action=none header.from=prevas.dk; Received: from AM0PR10MB1874.EURPRD10.PROD.OUTLOOK.COM (2603:10a6:208:3f::10) by AM0PR10MB2402.EURPRD10.PROD.OUTLOOK.COM (2603:10a6:208:e2::32) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3912.17; Wed, 10 Mar 2021 21:46:00 +0000 Received: from AM0PR10MB1874.EURPRD10.PROD.OUTLOOK.COM ([fe80::58b2:6a2a:b8f9:bc1a]) by AM0PR10MB1874.EURPRD10.PROD.OUTLOOK.COM ([fe80::58b2:6a2a:b8f9:bc1a%3]) with mapi id 15.20.3912.030; Wed, 10 Mar 2021 21:46:00 +0000 Subject: Re: [PATCH] [RFC] arm64: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION To: Masahiro Yamada , Nicholas Piggin Cc: Arnd Bergmann , Fangrui Song , Ard Biesheuvel , Arnd Bergmann , Andrew Scull , Mark Brown , Catalin Marinas , clang-built-linux , David Brazdil , Geert Uytterhoeven , Ionela Voinescu , Kees Cook , Kristina Martsenko , Linux ARM , "linux-kernel@vger.kernel.org" , Mark Rutland , Marc Zyngier , Nathan Chancellor , Nick Desaulniers , Vincenzo Frascino , Will Deacon , Nicolas Pitre References: <20210225112122.2198845-1-arnd@kernel.org> <20210226211323.arkvjnr4hifxapqu@google.com> <1614559739.p25z5x88wl.astroid@bobo.none> From: Rasmus Villemoes Message-ID: Date: Wed, 10 Mar 2021 22:45:58 +0100 User-Agent: Mozilla/5.0 (X11; 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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 10/03/2021 21.49, Masahiro Yamada wrote: > On Mon, Mar 1, 2021 at 10:11 AM Nicholas Piggin wrote: > > I tested LD_DEAD_CODE_DATA_ELIMINATION for the latest kernel. > > I added an unused function, this_func_is_unused(), > then built the ppc kernel with LD_DEAD_CODE_DATA_ELIMINATION. > > It remained in vmlinux. > > > masahiro@oscar:~/ref/linux$ echo 'void this_func_is_unused(void) {}' >>> kernel/cpu.c > masahiro@oscar:~/ref/linux$ export > CROSS_COMPILE=/home/masahiro/tools/powerpc-10.1.0/bin/powerpc-linux- > masahiro@oscar:~/ref/linux$ make ARCH=powerpc defconfig > masahiro@oscar:~/ref/linux$ ./scripts/config -e EXPERT > masahiro@oscar:~/ref/linux$ ./scripts/config -e LD_DEAD_CODE_DATA_ELIMINATION > masahiro@oscar:~/ref/linux$ > ~/tools/powerpc-10.1.0/bin/powerpc-linux-nm -n vmlinux | grep > this_func > c000000000170560 T .this_func_is_unused > c000000001d8d560 D this_func_is_unused Dunno, works just fine for my ppc32 target in v4.19 (i.e., the function gets eliminated when enabling LD_DEAD_CODE_DATA_ELIMINATION). But yes, I can reproduce for master ppc64 defconfig. kernel/.cpu.o.cmd says that it wasn't even compiled with -ffunction-sections, nor does .vmlinux.cmd mention --gc-sections. > masahiro@oscar:~/ref/linux$ grep DEAD_CODE_ .config > CONFIG_HAVE_LD_DEAD_CODE_DATA_ELIMINATION=y > CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=y Ah, but scripts/config just blindly adds that config option - I don't think ppc64 actually supports this, and CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=y automagically vanishes from .config when building. Rasmus _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel