[PATCH v4 0/2] Fix binfmt_flat loader for RISC-V

[Damien Le Moal]

RISC-V NOMMU flat binaries cannot tolerate a gap between the text and
data section as the toolchain fully resolves at compile time the PC
relative global pointer (__global_pointer$ value loaded in the gp
register). Without a relocation entry provided, the flat bin loader
cannot fix the value if a gap is introduced and user executables fail
to run.

This series fixes this problem by allowing an architecture to request
the flat loader to suppress the offset of the data start section.
Combined with the use of elf2flt "-r" option to mark the flat
executables with the FLAT_FLAG_RAM flag, the text and data sections are
loaded contiguously in memory, without a change in their relative
position from compile time.

The first patch fixes binfmt_flat flat_load_file() using the new
configuration option CONFIG_BINFMT_FLAT_NO_DATA_START_OFFSET. The
second patch enables this new option for RISCV NOMMU builds.

These patches do not change the binfmt_flat loader behavior for other
architectures.

Changes from v3:
* Renamed the configuration option from
  CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP to
  CONFIG_BINFMT_FLAT_NO_DATA_START_OFFSET to clarify that only the
  offseting of the data section start is suppressed.
* Do not force loding to RAM (contiguously) if the flat binary does not
  have the FLAT_FLAG_RAM flag set.
* Updated commit messages to reflect above changes.

Changes from v2:
* Updated distribution list
* Added Palmer ack-by tag

Changes from v1:
* Replace FLAT_TEXT_DATA_NO_GAP macro with
  CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP config option (patch 1).
* Remove the addition of riscv/include/asm/flat.h and set
  CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP for RISCV and !MMU

Damien Le Moal (2):
  binfmt_flat: allow not offsetting data start
  riscv: Disable data start offset in flat binaries

 arch/riscv/Kconfig |  1 +
 fs/Kconfig.binfmt  |  3 +++
 fs/binfmt_flat.c   | 19 ++++++++++++++-----
 3 files changed, 18 insertions(+), 5 deletions(-)

-- 
2.30.2