On Thu, Nov 12, 2015 at 07:36:02AM +0100, Ard Biesheuvel wrote: > On 12 November 2015 at 06:43, Shawn Guo <shawn....@linaro.org> wrote: > > Here are my questions: > > > > - Is this only because that ARM 64-bit toolchain doesn't show the real > > value of the pointers, or there are some linking or run-time magics to > > get these pointers correct when the binary is actually running? > > > > AArch64 uses the ELF RELA relocation format, where the target location > of the relocation is not used to hold the addend. In contrast, ARM > uses the REL format, where the addend is stored in the same place > where the result of the relocation computation needs to be stored. > > Since U-Boot is a PIE executable, it makes heavy use of > R_ARM_RELATIVE/R_AARCH64_RELATIVE relocations, which are not symbol > based, but simply point to places in the binary such as your init > array) where the offset between the link time and load time addresses > needs to be taken into account. For this type of relocation (and since > the u-boot link time base address is 0x0), the addends happen to > coincide with the actual addresses of the functions. These relocations > are applied at runtime by u-boot itself, since it moves itself to the > top of DRAM right after boot. > > In the AArch64 case, these addends are stored in the relocation > entries themselves. If you dump the relocations form the u-boot binary > using readelf, you will probably find the values you are looking for.
Thanks a lot for the pointer, Ard. With your hints, I'm looking at U-Boot commit 8137af19e75a (arm64: Add tool to statically apply RELA relocations) and getting the idea how this thing works on arm64. Thanks again. Shawn _______________________________________________ linaro-toolchain mailing list linaro-toolchain@lists.linaro.org https://lists.linaro.org/mailman/listinfo/linaro-toolchain
