[Qemu-devel] [ARM/FDPIC v4 0/4] FDPIC ABI for ARM

[Christophe Lyon <christophe.lyon@st.com>]

Hello,

This patch series implements the QEMU contribution of the FDPIC
ABI for ARM targets.

This ABI enables to run Linux on ARM MMU-less cores and supports
shared libraries to reduce the memory footprint.

Without MMU, text and data segment relative distances are different
from one process to another, hence the need for a dedicated FDPIC
register holding the start address of the data segment. One of the
side effects is that function pointers require two words to be
represented: the address of the code, and the data segment start
address. These two words are designated as "Function Descriptor",
hence the "FD PIC" name.

On ARM, the FDPIC register is r9 [3].

This work was developed some time ago by STMicroelectronics, and was
presented during Linaro Connect SFO15 (September 2015). You can watch
the discussion and read the slides [1].
This presentation was related to the toolchain published on github [2],
which is based on binutils-2.22, gcc-4.7, uclibc-0.9.33.2, gdb-7.5.1
and qemu-2.3.0, and for which pre-built binaries are available [2].

The ABI itself is described in details in [3].

Our Linux kernel patches have been updated and committed by Nicolas
Pitre (Linaro) in July 2017. They are required so that the loader is
able to handle this new file type. Indeed, the ELF files are tagged
with ELFOSABI_ARM_FDPIC. This new tag has been allocated by ARM, as
well as the new relocations involved.

This patch series has been rebased on top of QEMU from 2018-03-28.

I have also rebased the GCC patch series, but it is still WIP as
cleanup is still needed before I can request a review. It can be
useful to build a preview toolchain though, so my WIP branch is
available at [4].
To build such a toolchain, you'd also need to use my uClibc
branch [5].

I am currently working on updating the patches for the other toolchain
components, and will upstream them soon. This includes gcc, uclibc,
and gdb.

This series provides support for ARM v7 and later architectures and
has been used to run the GCC tests on arm-linux-gnueabi without
regression, as well as arm-linux-uclibceabi.

v3->v4:
- Fix nits in patch #3.

v2->v3:
- Do not add the is_fdpic field to TaskState, as the information can
  be retrieved from the 'info' data in TaskState.
- Setup_return() now returns an error if the FDPIC function
  description isn't readable. Callers of setup_return() are updated to
  force_sigsegv in such cases.

v1->v2:
- Patch #1 removes CONFIG_USE_FDPIC
- Patch #2 corresponds to the previous patch #1, and is now simpler
  without configure option
- Patch #3 corresponds to the previous patch #2, and uses TaskState
  instead of CPUARMState
- patch #4 corresponds to the previous patch #3, and fixes guest
  pointer dereferencing

Are the QEMU patches OK for inclusion in master?

Thanks,

Christophe.


[1] http://connect.linaro.org/resource/sfo15/sfo15-406-arm-fdpic-toolset-kernel-libraries-for-cortex-m-cortex-r-mmuless-cores/
[2] https://github.com/mickael-guene/fdpic_manifest
[3] https://github.com/mickael-guene/fdpic_doc/blob/master/abi.txt
[4] https://git.linaro.org/people/christophe.lyon/gcc.git/log/?h=fdpic-upstream
[5] https://git.linaro.org/people/christophe.lyon/uclibc.git/log/?h=uClibc-0.9.33.2-fdpic-upstream

Christophe Lyon (4):
  Remove CONFIG_USE_FDPIC.
  linux-user: ARM-FDPIC: Identify ARM FDPIC binaries
  linux-user: ARM-FDPIC: Add support of FDPIC for ARM.
  linux-user: ARM-FDPIC: Add support for signals for FDPIC targets

 include/elf.h        |   1 +
 linux-user/elfload.c |  54 ++++++++++++++++++++------
 linux-user/qemu.h    |  13 ++++++-
 linux-user/signal.c  | 105 +++++++++++++++++++++++++++++++++++++++++++--------
 4 files changed, 144 insertions(+), 29 deletions(-)

-- 
2.6.3