linux-kernel - Re: [PATCH v3] riscv: explicitly use symbol offsets for VDSO

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Date:   Wed, 27 Oct 2021 16:50:33 +0200
From:   Andreas Schwab <schwab@...ux-m68k.org>
To:     Saleem Abdulrasool <abdulras@...gle.com>
Cc:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Palmer Dabbelt <palmer@...belt.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Bill Wendling <morbo@...gle.com>,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH v3] riscv: explicitly use symbol offsets for VDSO

On Aug 04 2021, Saleem Abdulrasool wrote:

> The current implementation of the `__rt_sigaction` reference computed an
> absolute offset relative to the mapped base of the VDSO.  While this can
> be handled in the medlow model, the medany model cannot handle this as
> it is meant to be position independent.  The current implementation
> relied on the BFD linker relaxing the PC-relative relocation into an
> absolute relocation as it was a near-zero address allowing it to be
> referenced relative to `zero`.
>
> We now extract the offsets and create a generated header allowing the
> build with LLVM and lld to succeed as we no longer depend on the linker
> rewriting address references near zero.  This change was largely
> modelled after the ARM64 target which does something similar.
>
> Signed-off-by: Saleem Abdulrasool <abdulras@...gle.com>

I think this broke out-of-tree module builds.

https://build.opensuse.org/package/live_build_log/openSUSE:Factory:RISCV/rtl8812au/standard/riscv64

+ make -j4
make ARCH=riscv CROSS_COMPILE= -C /usr/src/linux-obj/riscv64/default M=/home/abuild/rpmbuild/BUILD/rtl8812au-5.9.3.2+git20210427.6ef5d8f/obj/default  modules
make[1]: Entering directory '/usr/src/linux-5.14.14-1-obj/riscv64/default'
mkdir: cannot create directory 'arch/riscv/kernel': Permission denied
  LDS     arch/riscv/kernel/vdso/vdso.lds
  AS      arch/riscv/kernel/vdso/rt_sigreturn.o
  CC      arch/riscv/kernel/vdso/vgettimeofday.o
  AS      arch/riscv/kernel/vdso/getcpu.o
mkdir: cannot create directory 'arch/riscv/kernel': Permission denied
  LDS     arch/riscv/kernel/vdso/vdso.lds
  AS      arch/riscv/kernel/vdso/rt_sigreturn.o
  CC      arch/riscv/kernel/vdso/vgettimeofday.o
  AS      arch/riscv/kernel/vdso/getcpu.o
cc1: fatal error: opening output file arch/riscv/kernel/vdso/vdso.lds: No such file or directory
compilation terminated.
make[3]: *** [/usr/src/linux-5.14.14-1/scripts/Makefile.build:366: arch/riscv/kernel/vdso/vdso.lds] Error 1

Andreas.

-- 
Andreas Schwab, schwab@...ux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."