* Add RISC-V support
This patch adds support for the RISC-V architecture (https://riscv.org).
This patch has been tested using QEMU user-mode emulation and GCC 7.2.0
in the following configurations:
* -march=rv32imac -mabi=ilp32
* -march=rv32g -mabi=ilp32d
* -march=rv64imac -mabi=lp64
* -march=rv64g -mabi=lp64d
The ABI currently can be found at
https://github.com/riscv/riscv-elf-psabi-doc/blob/master/riscv-elf.md .
* Add RISC-V to README
* RISC-V: fix configure.host
This change fixes libffi.call/struct10.c failure on ia64:
FAIL: libffi.call/struct10.c -W -Wall -Wno-psabi -O0 execution test
.Lst_small_struct handles returns for structs less than 32 bytes
(following ia64 return value ABI [1]). Subroutine does roughly the
following:
```
mov [sp+0] = r8
mov [sp+8] = r9
mov [sp+16] = r10
mov [sp+24] = r11
memcpy(destination, source=sp, 12);
```
The problem: ia64 ABI guarantees that top 16 bytes of stack are
scratch space for callee function. Thus it can clobber it. [1]
says (7.1 Procedure Frames):
"""
* Scratch area. This 16-byte region is provided as scratch storage
for procedures that are called by the current procedure. Leaf
procedures do not need to allocate this region. A procedure may
use the 16 bytes at the top of its own frame as scratch memory,
but the contents of this area are not preserved by a procedure call.
"""
In our case 16 top bytes are clobbered by a PLT resolver when memcpy()
is called for the first time. As a result memcpy implementation reads
already clobbered data frop top of stack.
The fix is simple: allocate 16 bytes of scrats space prior to memcpy()
call.
[1]: https://www.intel.com/content/dam/www/public/us/en/documents/guides/itanium-software-runtime-architecture-guide.pdf
Bug: https://bugs.gentoo.org/634190
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
Anthony Green
Stef O'Rear
Andreas Schwab
Sergei Trofimovich