Resolves #216

Use of asm aliased register variables in local scope can only be used
for extended assembly parameters.  This changes the few instances of
this in the floating point emulation to use the GNU extended assembly
syntax to access the `tp` register.  This ensures that we do not rely on
undefined behaviour.  This was uncovered when building the Proxy kernel
with clang and LLVM.

The use of `asm` for register aliasing is supported in two different
contexts:
- local variables (including GNU expression statements) where it may
  only be used for specifying registers for input and output operands to
  extended `asm` syntax.

  c.f. https://gcc.gnu.org/onlinedocs/gcc/Local-Register-Variables.html#Local-Register-Variables

- global variables where it may be used to observe the contents of a
  register.

  c.f. https://gcc.gnu.org/onlinedocs/gcc/Global-Register-Variables.html#Global-Register-Variables

The two options here is to either to hoist the variable out into a
global variable, but then it should not be in a header due to fears of
ODR in case the optimizer does not inline it away, and thus becomes a
bit more tricky.  The alternative that this change actually adopts is to
explicitly use a move to copy the value out via the GNU extended
assembly syntax.

With this change, it is now possible to build the Proxy Kernel
completely with clang/LLVM and link with LLD.  The generated kernel also
runs under SPIKE and behaves as expected in a simple smoke test (without
any executable prints the expected message, and runs a trivial RVV
example).

This is an equivalent rewrite of the existing code.  When building with
gas, the `bltu` would implicitly get relaxed to the `bgeu` + `j`.  This
relaxation is required as the `init_other_hart` is not guaranteed to be
addressable in 12-bits.  When building with the LLVM IAS instead of gas
we fail to link as the branch is not relaxed.  This change enables LLVM
to build and link this code with the LLVM IAS and lld.

The LLVM IAS currently does not support the older spelling for the CSR.
Update the references to the modern name.

The LLVM IAS does not support the older name for the `mtval` CSR.  This
updates the name to the current spelling, which is required to build
with the LLVM IAS.  This remains compatible with binutils as well.

This replaces use of the old `sbadaddr` CSR name with the current
`stval` name.  The old spelling is not supported by the LLVM IAS,
however, the modern spelling is supported by both LLVM and binutils.

Using recent compilers we get the following error message:

  ../pk/pk.c: In function 'run_loaded_program.constprop':
  ../pk/pk.c:177:3: error: both arguments to '__builtin___clear_cache'
  must be pointers
    177 |   __clear_cache(0, 0);
        |   ^~~~~~~~~~~~~~~~~~~

Let's use the existing function __riscv_flush_icache(),
give it a header with a prototype and use it to
emits the FENCE.I instruction directly.

See #239

Suggested-by: Andrew Waterman <andrew@sifive.com>
Signed-off-by: Christoph Muellner <cmuellner@linux.com>

The upstream LiteX project defaults to "litex,liteuart" as the value
for the "compatible" property of the UART DT node, so let's add it to
the current list of accepted strings.

Signed-off-by: Gabriel Somlo <gsomlo@gmail.com>

This assumes that stval is populated with the opcode on illegal
instruction exceptions.  But since we're only using the opcode for
error reporting, it's OK if this assumption is violated.

Previously, the pk would always run from virtual address MEM_START.
Instead, remap it into the negative virtual addresses, allowing user
processes to expand beyond MEM_START.

Return the old brk if mmap fails, rather than just asserting out

Estimate available memory and return -1 from mmap if not enough
is available, rather than assert-failing.

This will improve flexibility going forward.

Enforced with sstatus.SUM.

Tested using the RocketChip CPU option.
(see https://github.com/enjoy-digital/litex

)

Signed-off-by: Gabriel Somlo <gsomlo@gmail.com>

Remove use of copy_stat() from sys_fstatat

The system call should return the stat struct in kernel format, not
libc format.

Big endian

The linux kernel pushes argc as an int, not an uintptr_t.
(The offset to the next element is still sizeof(uintptr_t).)

* add device tree in elf, using --with-dts to add the absolute path of device tree

* Disable device tree filter

* Remove *.dtb dependence, when the --with-dts option is not used

This reverts commit a161e6f3.

Resolves #218

* add device tree in elf, using --with-dts to add the absolute path of device tree

* Disable device tree filter