why ld.so loading EXEC/DYN elf behaves differently in term of the same dependent so? EXEC – loading dependency so according to So ELF header (fixed virtual address which is defined by LD script during creating of the so) DYN - loading dependency so randomly. Appreciate if someone could help. 😊 Xinghao Chen (陈行浩) From: Xing-Hao Chen Sent: 2019年12月11日 17:33 To: gcc-help@xxxxxxxxxxx Subject: help! why a 'so' can't load its dependent 'so' to the pre-defined address Dear GCC experts Please forgive me if it’s bothering you. I have a question about LD and dynamic library, which I have been struggling with for a while it will be great if you can help me out, in my program, two "so" - libcpss.so and libhelper.so have to be loaded into a fixed virtual address, it’s done by the ld script, SECTIONS { /* Code section, access rights RX */ . = 0x14600000; … } readelf -l libhelper.so | less Elf file type is DYN (Shared object file) Entry point 0x14607ad8 There are 8 program headers, starting at offset 64 Program Headers: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flags Align LOAD 0x0000000000010000 0x0000000014600000 0x0000000014600000 0x000000000001aaec 0x000000000001aaec R E 0x10000 an elf program(appDemo) linked with these two ".so", we can see the two so indeed were loaded into the expected fixed address, ldd ./appDemo linux-vdso.so.1 => (0x0000ffff917ec000) libcpss.so => ./libcpss.so (0x0000000010000000) libhelper.so => ./libhelper.so (0x0000000014600000) libpthread.so.0 => /lib/aarch64-linux-gnu/libpthread.so.0 (0x0000ffff917b5000) librt.so.1 => /lib/aarch64-linux-gnu/librt.so.1 (0x0000ffff9179d000) libdl.so.2 => /lib/aarch64-linux-gnu/libdl.so.2 (0x0000ffff91789000) libm.so.6 => /lib/aarch64-linux-gnu/libm.so.6 (0x0000ffff916d7000) libc.so.6 => /lib/aarch64-linux-gnu/libc.so.6 (0x0000ffff91583000) /lib/ld-linux-aarch64.so.1 (0x0000aaaadd94f000) however, i built another "so" – libtestScript.so that linking(depending on) these two so, seems not able to load these two so into proper fixed address, see below - ldd ./libtestScript.so linux-vdso.so.1 => (0x0000ffff8d87c000) libcpss.so => ./libcpss.so (0x0000ffff89d50000) libhelper.so => ./libhelper.so (0x0000ffff5e350000) libpthread.so.0 => /lib/aarch64-linux-gnu/libpthread.so.0 (0x0000ffff5e31c000) librt.so.1 => /lib/aarch64-linux-gnu/librt.so.1 (0x0000ffff5e304000) libdl.so.2 => /lib/aarch64-linux-gnu/libdl.so.2 (0x0000ffff5e2f0000) libm.so.6 => /lib/aarch64-linux-gnu/libm.so.6 (0x0000ffff5e23e000) libc.so.6 => /lib/aarch64-linux-gnu/libc.so.6 (0x0000ffff5e0ea000) /lib/ld-linux-aarch64.so.1 (0x0000aaaae0958000) do i missed any LD flags during building of the “joint .so" ? i saw the only difference between elf main program and “joint” so is the flag of “-shared”, so why “joint .so" missed the info of the two dependent so’s loading address? seems when the ld.so load "joint .so" and try to resolve and load the dependency two ".so", but it doesn't load them into the fixed address(0x10000000 / 0x14600000) NOK: LD_DEBUG=all ldd ./libtestScript.so 2349: file=libhelper.so [0]; generating link map 2349: dynamic: 0x0000ffff5d581ba0 base: 0x0000ffff48f57000 size: 0x000000002b9ff004 2349: entry: 0x0000ffff5d55ead8 phdr: 0x0000ffff8ca6fcc0 phnum: 8 OK: LD_DEBUG=all ldd ./appDemo 2289: trying file=./libhelper.so 2289: 2289: file=libhelper.so [0]; generating link map 2289: dynamic: 0x000000001462aba0 base: 0x0000000000000000 size: 0x000000002b9ff004 2289: entry: 0x0000000014607ad8 phdr: 0x0000ffffb2e24cc0 phnum: 8 readelf -h ./libhelper.so ELF Header: Magic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 Class: ELF64 Data: 2's complement, little endian Version: 1 (current) OS/ABI: UNIX - System V ABI Version: 0 Type: DYN (Shared object file) Machine: AArch64 Version: 0x1 Entry point address: 0x14607ad8 Start of program headers: 64 (bytes into file) Start of section headers: 228680 (bytes into file) Flags: 0x0 Size of this header: 64 (bytes) Size of program headers: 56 (bytes) Number of program headers: 8 Size of section headers: 64 (bytes) Number of section headers: 34 Section header string table index: 31 i appreciate if you can help me out. For your reference on how I built the elf executable program and shared lib. /home/ericxh/work/toolchain/marvell-gcc-5.2.1-16.02.0-armv8/armv8/le/aarch64v8- marvell-linux-gnu-5.2.1_i686_20151110/bin/aarch64-marvell-linux-gnu-gcc -shared -Xlinker --whole-archive compilation_root/cpss_4.2/armv8_DX_SHARED/cpssEnabler/libs/TESTSCRIPT.a -Xlinker --no-whole-archive \ compilation_root/cpss_4.2/armv8_DX_SHARED/libcpss.so compilation_root/cpss_4.2/armv8_DX_SHARED/libhelper.so -Xlinker -z -Xlinker nocopyreloc -rdynamic -lpthread -lrt -ldl -lm -Xlinker -Map -Xlinker compilation_root/cpss_4.2/armv8_DX_SHARED/libtestScript.map \ -Xlinker -soname - Xlinker libtestScript.so -o compilation_root/cpss_4.2/armv8_DX_SHARED/libtestScript.so /home/ericxh/work/toolchain/marvell-gcc-5.2.1-16.02.0-armv8/armv8/le/aarch64v8- marvell-linux-gnu-5.2.1_i686_20151110/bin/aarch64-marvell-linux-gnu-gcc -Xlinker --whole-archive compilation_root/cpss_4.2/armv8_DX_SHARED/referenceCode/libs/REFERENCECODE.a … … compilation_root/cpss_4.2/armv8_DX_SHARED/cpssEnabler/libs/CPSSAPPREF.a compilation_root/cpss_4.2/armv8_DX_SHARED/version_info.o -Xlinker --no-whole- archive \ compilation_root/cpss_4.2/armv8_DX_SHARED/libcpss.so compilation_root/cpss_4.2/armv8_DX_SHARED/libhelper.so -Xlinker -z -Xlinker nocopyreloc -rdynamic -lpthread -lrt -ldl -lm -Xlinker -Map -Xlinker compilation_root/cpss_4.2/armv8_DX_SHARED/appDemo.map -o compilation_root/cpss_4.2/armv8_DX_SHARED/appDemo Best regards Xinghao Chen (陈行浩)