[PATCH v2 0/2] deal with GOT stuff for RISC-V

* [PATCH v2 0/2] deal with GOT stuff for RISC-V
@ 2023-03-16 13:22 Oleksii Kurochko
  2023-03-16 13:22 ` [PATCH v2 1/2] xen/riscv: add EMBEDDED_EXTRA_CFLAGS to CFLAGS Oleksii Kurochko
                   ` (3 more replies)
  0 siblings, 4 replies; 13+ messages in thread
From: Oleksii Kurochko @ 2023-03-16 13:22 UTC (permalink / raw)
  To: xen-devel
  Cc: Jan Beulich, Andrew Cooper, Stefano Stabellini, Gianluca Guida,
	Oleksii Kurochko, Bob Eshleman, Alistair Francis, Connor Davis

The patch series introduces things to deal with GOT stuff whichwas faced
during the work on [1].

Initially, the issue was with 'la' pseudo instruction, which transformed to
'aupic/l{w|d} GOT' instead of 'auipc/addi'.
The transformation dependson .option {nopic, pic} directive 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_and addresses inside GOT
sections will be relative to linker time addresses.

At least there are two reasons for that:
1. GCC compiler used in RISCV64 container is compiled with
  --enable-default-pie flag.
2. GCC spec file for the RISC-V architecture by default enabled -fpic:
   [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

To resolve that, it was added EMBEDDED_EXTRA_CFLAGS to RISCV's CFLAGS as it was
done for other architecture.

To catch use cases when GOT things will be produced by something was createthe
second patch of the patch series:
[xen/riscv: add explicit check that.got{.plt} is empty] which add .got&.got.plt
sections to xen.lds.S and alsoadds asserts to check that the mentioned sections
are empty otherwise, it will be produced a compilation error with the message
that the sections aren't empty.

[1]:
https://lore.kernel.org/xen-devel/22c46432-e940-914e-53c2-2913607be3e2@suse.com/T/#t

---
Changes in V2:
 * The patch [1] was refactored and lead to the patch [xen/riscv: add
   EMBEDDED_EXTRA_CFLAGS to CFLAGS].
 * In addition to the patch [1] was created another patch [xen/riscv: add explicit
   check that .got{.plt} is empty] to be sure that .got{.plt} sections
   weren't produced.
---
Oleksii Kurochko (2):
  xen/riscv: add EMBEDDED_EXTRA_CFLAGS to CFLAGS
  xen/riscv: add explicit check that .got{.plt} is empty

 xen/arch/riscv/arch.mk   |  2 ++
 xen/arch/riscv/xen.lds.S | 13 +++++++++++++
 2 files changed, 15 insertions(+)

-- 
2.39.2

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