deal with GOT stuff for RISC-V

[PATCH v2 1/2] xen/riscv: add EMBEDDED_EXTRA_CFLAGS to CFLAGS

Posted by Oleksii Kurochko 2 years, 9 months ago

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 <oleksii.kurochko@gmail.com>
---
 Changes in V2:
 * instead of changing 'la' to 'lla' to keep cpu0_boot_stack PC-relative
   it was updated CFLAGS with EMBEDDED_EXTRA_CFLAGS which contains
   -fno-PIE thereby 'la' will be transformed to 'auipc/addi' without
   GOT usage.
 * update the commit message with additional details.
---
 xen/arch/riscv/arch.mk | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/xen/arch/riscv/arch.mk b/xen/arch/riscv/arch.mk
index 45fe858ee0..7448f759b4 100644
--- a/xen/arch/riscv/arch.mk
+++ b/xen/arch/riscv/arch.mk
@@ -1,6 +1,8 @@
 ########################################
 # RISCV-specific definitions
 
+$(call cc-options-add,CFLAGS,CC,$(EMBEDDED_EXTRA_CFLAGS))
+
 CFLAGS-$(CONFIG_RISCV_64) += -mabi=lp64
 
 riscv-march-$(CONFIG_RISCV_ISA_RV64G) := rv64g
-- 
2.39.2

Re: [PATCH v2 1/2] xen/riscv: add EMBEDDED_EXTRA_CFLAGS to CFLAGS

Posted by Alistair Francis 2 years, 8 months ago

On Thu, Mar 16, 2023 at 11:22 PM Oleksii Kurochko
<oleksii.kurochko@gmail.com> 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 <oleksii.kurochko@gmail.com>

Acked-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>  Changes in V2:
>  * instead of changing 'la' to 'lla' to keep cpu0_boot_stack PC-relative
>    it was updated CFLAGS with EMBEDDED_EXTRA_CFLAGS which contains
>    -fno-PIE thereby 'la' will be transformed to 'auipc/addi' without
>    GOT usage.
>  * update the commit message with additional details.
> ---
>  xen/arch/riscv/arch.mk | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/xen/arch/riscv/arch.mk b/xen/arch/riscv/arch.mk
> index 45fe858ee0..7448f759b4 100644
> --- a/xen/arch/riscv/arch.mk
> +++ b/xen/arch/riscv/arch.mk
> @@ -1,6 +1,8 @@
>  ########################################
>  # RISCV-specific definitions
>
> +$(call cc-options-add,CFLAGS,CC,$(EMBEDDED_EXTRA_CFLAGS))
> +
>  CFLAGS-$(CONFIG_RISCV_64) += -mabi=lp64
>
>  riscv-march-$(CONFIG_RISCV_ISA_RV64G) := rv64g
> --
> 2.39.2
>
>

Re: [PATCH v2 1/2] xen/riscv: add EMBEDDED_EXTRA_CFLAGS to CFLAGS

Posted by Jan Beulich 2 years, 9 months ago

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 <oleksii.kurochko@gmail.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>

There may also want to be Suggested-by to both Andrew and me.

Jan

[PATCH v2 1/2] xen/riscv: add EMBEDDED_EXTRA_CFLAGS to CFLAGS
[PATCH v2 2/2] xen/riscv: add explicit check that .got{.plt} is empty