Hi, (pls CC me when replying because I am not subscriber) I met an interesting phenomenon when looking into linux kernel compilation, it can be simply summarized as following: in arch/x86/boot/compressed, memcpy is defined as __builtin_memcpy, while also implemented as a function. But when using memcpy, in some case GCC optimize it to inline code, in other case GCC just emit a call to self-defined memcpy function. This can be confirmed according to the symbol table via `nm bluh.o`. The compiling flags is, for example: cmd_arch/x86/boot/compressed/pgtable_64.o := gcc -Wp,-MD,arch/x86/boot/compressed/.pgtable_64.o.d -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/8/include -I./arch/x86/include -I./arch/x86/include/gene rated -I./include -I./arch/x86/include/uapi -I./arch/x86/include/generated/uapi -I./include/uapi -I./include/generated/uapi -include ./include/linux/kconfig.h -include ./include/linux/compiler_types.h -D__KERNEL__ -DCONFIG_CC_STACKPROTECTOR -m64 -O2 -fno-strict-aliasing -fPIE -DDISABLE_BRANCH_PROFILING -mcmodel=small -mno-mmx -mno-sse -ffreestanding -fno-stack-protector -DKBUILD_BASENAME='"pgtable_64"' -DKBUILD_MODNAME='"pgtable_64"' -c -o arch/x86/boot/compressed/pgtable_64.o arch/x86/boot/compressed/pgtable_64.c Now the questions is: from code-reading, it is kind of non-intuitive, is there any explicit way to control the optimization behavior accurately? -- Sincerely, Cao jin
