GuoMinskey <minskey_guo@xxxxxxxxxxx> writes: > On x86 platform, Âis there any means to link 32 bit ELF output intoÂ64 bit Â? > In Linux kernel, Âarch/x86/boot/compressed/head_64.S, Â starts from32-bit codeÂand enables CPU to jump into 64-bit. ÂSo, that file isÂassembledÂinto 64 bit ELFÂobject with mixed 32/64 bit code. > Now, I want to call a routine from somewhere in the 32bit code partÂof head_64.S. Â ÂAnd I write the routine by C language, Âsay test.cÂand compile Âit with "gcc -m32 -c -o test.o". Â ÂHow can I link mytest.o to head_64.o ? ÂOr I have to use assembly language to rewritemy routine and embed it directly into head_64.S source code ? On x86, 32-bit code can not call 64-bit code, nor vice-versa. The Linux kernel uses some tricks to start up in 32-bit mode, convert to 64-bit mode, and branch to 64-bit code as it converts. You can't do the same tricks yourself; only the kernel can do them. So, the answer is that you can link 32-bit and 64-bit code together easily enough, using the linker's -b option as the kernel build does, but you can't do anything useful with the result. Ian
