On 16.03.2023 14:22, Oleksii Kurochko wrote:
> The patch is needed to keep all address of cpu0_boot_stack
> PC-relative.
>
> Pseudoinstruction 'la' can be transformed to 'auipc/addi' or
> 'auipc/l{w|d}'. It depends on the .option directive: nopic and pic
> or compiler flags.
>
> Right now, 'la' transforms to 'auipc/l{w|d}', which in case of
> cpu0_boot_stack[] will lead to the usage of _GLOBAL_OFFSET_TABLE_
> where all addresses will be without counting that it might happen
> that linker address != load address ( so addresses inside got
> sections will be relative to linker time ).
>
> It happens becuase the compiler from riscv64 docker compiled with
> --enable-default-pie:
> [user@49295ae49cbe build]$ riscv64-linux-gnu-gcc -v
> Using built-in specs.
> COLLECT_GCC=riscv64-linux-gnu-gcc
> COLLECT_LTO_WRAPPER=/usr/lib/gcc/riscv64-linux-gnu/12.2.0/lto-wrapper
> Target: riscv64-linux-gnu
> Configured with: /build/riscv64-linux-gnu-gcc/src/gcc-12.2.0/configure
> --prefix=/usr --program-prefix=riscv64-linux-gnu- --with-local-
> prefix=/usr/riscv64-linux-gnu --with-sysroot=/usr/riscv64-linux-gnu --
> with-build-sysroot=/usr/riscv64-linux-gnu --libdir=/usr/lib --
> libexecdir=/usr/lib --target=riscv64-linux-gnu --host=x86_64-pc-linux-
> gnu --build=x86_64-pc-linux-gnu --with-system-zlib --with-isl --with-
> linker-hash-style=gnu --disable-nls --disable-libunwind-exceptions --
> disable-libstdcxx-pch --disable-libssp --disable-multilib --disable-
> werror --enable-languages=c,c++ --enable-shared --enable-threads=posix
> --enable-__cxa_atexit --enable-clocale=gnu --enable-gnu-unique-object -
> -enable-linker-build-id --enable-lto --enable-plugin --enable-install-
> libiberty --enable-gnu-indirect-function --enable-default-pie --enable-
> checking=release
> Thread model: posix
> Supported LTO compression algorithms: zlib zstd
> gcc version 12.2.0 (GCC)
>
> Looking at gcc spec file for the RISC-V architecture:
> [user@49295ae49cbe build]$ riscv64-linux-gnu-gcc -dumpspecs | grep -i
> pic
> --traditional-format %(subtarget_asm_debugging_spec) %{fno-pie|fno-
> PIE|fno-pic|fno-PIC:;:-fpic} %{march=*} %{mabi=*} %{mno-relax} %{mbig-
> endian} %{mlittle-endian} %(subtarget_asm_spec)%{misa-spec=*}
> which means that -fpic is enabled if none of the following options are
> present on the command line:
> -fno-pie
> -fno-PIE
> -fno-pic
> -fno-PIC
>
> That's the reasons why 'la' is transformed to 'aupic/l{w|d} GOT' and
> not be dependent on the toolchain used.
>
> Signed-off-by: Oleksii Kurochko <[email protected]>
Reviewed-by: Jan Beulich <[email protected]>
There may also want to be Suggested-by to both Andrew and me.
Jan
