[Mono-dev] [PATCH] more support for Google Native Client

Rodrigo Kumpera kumpera at gmail.com
Sat Dec 25 08:01:35 EST 2010

Hi Elijah,

The patchset is indeed huge and will take quite some review effort to get it
in. I'll start by reviewing the bug fixes then move to ILP32 support.

Since you guys had to add GC support for cooperative parking, it would be
interesting to merge this effort with the current one toward adding it
to sgen, which has received quite some reviewing and testing. Mark Probst
can better talk about it once he gets back from his vacations.

One problem I see in the general description of how parking is been done is
that it doesn't handle blocking syscalls, which might lead to a single
thread make the GC halt.

I'll start reviewing/cherry picking patches next year once I get back to
work. Just wanted to give you a heads up.

On Tue, Dec 21, 2010 at 6:12 PM, Elijah Taylor <elijahtaylor at google.com>wrote:

> Greetings Mono developers!
> *[tl;dr  very large patch for Native Client<http://www.chromium.org/nativeclient> support
> hosted here <https://github.com/elijahtaylor/mono>, would love feedback
> and many eyes to look at it]
> *
> I'm back with another round of changes for supporting Google's Native
> Client (NaCl), including support for amd64, JIT compilation, and Garbage
> Collection.  It's a large set of changes, forked on Dec 14 in github @
> https://github.com/elijahtaylor/mono.  I would appreciate feedback on
> these changes... to facilitate this, I'll try to explain the largest changes
> by feature (please email if clarification is needed):
> *1) amd64 codegen*
>    - Rules located here:
>    http://www.chromium.org/nativeclient/design-documents/nacl-sfi-model-on-x86-64-systems
>       - Removed %r15 from register allocation, LMF save/restore, etc.
>        (r15 is special and not modifiable by untrusted code)
>       - Sandbox all data access through membase address mode.  If not %rsp
>       or %rbp relative, re-write as clearing upper 32-bits + memindex addressing
>       - align functions, call sites
>       - Sandbox returns and all indirect jumps (need to be 32-byte
>       aligned, cleared upper 32-bits)
>       - Never omit frame pointer as general operations to rbp aren't
>       allowed
> *2) NaCl x86-64 is ILP32 (this is the largest set of changes and may make
> some mono devs unhappy)*
>    - Set SIZEOF_REGISTER == 8 while sizeof(gpointer) == 4 for NaCl amd64
>    (we can use 8-byte instructions, but pointers are 4-bytes)
>    - Re-write large portions of mini-amd64.c, tramp-amd64.c,
>    exceptions-amd64.c, mini.c, method-to-ir.c to use appropriate sizes
>    (SIZEOF_REGISTER, sizeof(gpointer), literal '8').  *These changes are
>    disruptive, but ultimately they should be more correct than what was there
>    before.  *It's our opinion that these changes actually improve Mono
>    despite their impact.
>    - We only generate NaCl amd64 code from an ILP32 machine (either a
>    32-bit application for AOT code, or NaCl runtime JIT), so we may not have
>    caught all of the [8 <--> SIZEOF_REGISTER] conversions, but we likely caught
>    most of the [sizeof(gpointer) <--> SIZEOF_REGISTER] and [8 <-->
>    sizeof(gpointer)] changes that are necessary.
>    - Change atomic operations and default pointer directives to use 32-bit
>    instructions (long instead of quad)
>    - Change default operations to use 32-bit integers/pointers (eg,
>    OP_LOAD_MEMBASE uses 4-bytes instead of 8)
> *3) JIT support for NaCl*
>    - Since we're unable to emit code directly in its final executable
>    location, we instead:
>       - reserve a buffer on the heap
>       - create a hash table entry mapping the temp location and final
>       location
>       - modify all non-local patches relative to the final location
>       - request the NaCl runtime to install the created code in the final
>       location
>    - See mono/utils/mono-codeman.c changes for more detail.
>    - For every codeman *reserve*, we must add a codeman *validate* call in
>    order to install the method/trampoline/blob in the final location (as well
>    as validate it for NaCl, pad it out, etc)
>    - We don't delete or reuse code  (we can, but it's icky and the
>    benefits don't outweigh the cost)
>    - Backpatching changed to use NaCl syscalls to modify existing dynamic
>    code
> *4) GC support for NaCl (boehm only)*
>    - NaCl compiler and Mono code generator both emit instrumentation at GC
>    "safe points" (back branches and function prologs), for cooperative thread
>    parking (we're not allowed to send and receive signals)
>    - Added new opcode OP_NACL_GC_SAFE_POINT to handle mono instrumentation
>    - modified pthread_stop_world.c and pthread_support.c somewhat
>    extensively to support this new way of stopping the world
>    - wrapped pthread_exit because NaCl doesn't support pthread cleanup
>    functions
>    - added machine type NACL to libgc with machine specific defines
> *5) Misc bug fixes (not NaCl-specific)*
>    - fix *x86_memindex_emit* when disp is 32-bit
>    - properly exclude code in libgc/gc_dlopen.c when DYNAMIC_LOADING not
>    defined
>    - properly exclude code based on DISABLE_SOCKETS by including config.h
>    before checking define
>    - clean up calculation of offset for amd64 AOT specific trampoline args
>    - fix bug in *mono_bblock_insert_before_ins* when trying to insert an
>    instruction to the beginning of an existing basic block.
>    - fix small typo bug in genmdesc.pl which kept amd64 from being able to
>    be a target of cross compiling
>    - fix struct passing in amd64 with sizeof(struct) == 16 when fields
>    aren't 8-byte aligned (eg, first field is 12 bytes, second field is 4
>    bytes), pass on stack instead of in registers (mini-amd64.c:*
>    add_valuetype*)
>    - add extra checks to mini-amd64.c:*mono_arch_emit_exceptions* to keep
>    exception/R4/R8 emitting from overflowing a buffer silently
>    - fix bugs in *new_codechunk* and *mono_code_manager_reserve_align*which allowed unaligned code to be allocated.
> I know we're close to holidays so I don't have any delusions that these
> changes will get in by the end of the year :)  Please feel free to pick
> apart these changes and let me know if there are things that should be
> changed.
> -Elijah
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