With dynamic linking we have the current limitation that there can be
only a single active data segment (since we use __memory_base as the
load address and we can't do arithmetic in constant expresions).
This change delays the merging of active segments until a little later
in the linking process which means that the grouping of data by section,
and the magic __start/__end symbols work as expected under dynamic
linking.
Differential Revision: https://reviews.llvm.org/D96453
We have two types of relocations that we apply on startup:
1. Relocations that apply to wasm globals
2. Relocations that apply to wasm memory
The first set of relocations use only the `__memory_base` import to
update a set of internal globals. Because wasm globals are thread local
these need to run on each thread. Memory relocations, like static
constructors, must only be run once.
To ensure global relocations run on all threads and because the only
depend on the immutable `__memory_base` import we can run them during
the WebAssembly start functions, instead of waiting until the
post-instantiation __wasm_call_ctors.
Differential Revision: https://reviews.llvm.org/D93066
This change improves our support for shared memory to include
PIC executables (and shared libraries).
To handle this case the linker-generated `__wasm_init_memory`
function (that only exists in shared memory builds) must be
capable of loading memory segements at non-const offsets based
on the runtime value of `__memory_base`.
Differential Revision: https://reviews.llvm.org/D92620
The conditional guarding createInitMemoryFunction was incorrect and
didn't match that guarding the creation of the associated symbol.
Rather that reproduce the same conditions in multiple places we can
simply use the presence of the associated symbol.
Also, add an assertion that would have caught this bug.
Also, add a new test for this flag combination.
This is part of an ongoing effort to enable dynamic linking with
threads in emscripten.
See https://github.com/emscripten-core/emscripten/issues/3494
Differential Revision: https://reviews.llvm.org/D92520
Summary:
This patch fixes a bug where initialization code for .bss segments was
emitted in the memory initialization function even though the .bss
segments were discounted in the datacount section and omitted in the
data section. This was producing invalid binaries due to out-of-bounds
segment indices on the memory.init and data.drop instructions that
were trying to operate on the nonexistent .bss segments.
Reviewers: sbc100
Subscribers: dschuff, jgravelle-google, aheejin, sunfish, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D80354
Summary:
WebAssembly memories are zero-initialized, so when module does not
import its memory initializing .bss sections is guaranteed to be a
no-op. To reduce binary size and initialization time, .bss sections
are simply not emitted into the final binary unless the memory is
imported.
Reviewers: sbc100
Subscribers: dschuff, jgravelle-google, aheejin, sunfish, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D68965
llvm-svn: 374940
Summary:
This was always the intended behavior, but had not been
implemented. This ordering is important for Emscripten when generating
.mem files while compiling to JS, since only zeros at the end of
initialized memory can be dropped.
Fixes https://github.com/emscripten-core/emscripten/issues/8999
Reviewers: sbc100
Subscribers: dschuff, jgravelle-google, aheejin, sunfish, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D67736
llvm-svn: 372284
Summary:
- `__wasm_init_memory` is now the WebAssembly start function instead
of being called from `__wasm_call_ctors` or called directly by the
runtime.
- Adds a new synthetic data symbol `__wasm_init_memory_flag` that is
atomically incremented from zero to one by the thread responsible
for initializing memory.
- All threads now unconditionally perform data.drop on all passive
segments.
- Removes --passive-segments and --active-segments flags and controls
segment type based on --shared-memory instead. The deleted flags
were only present to ameliorate the upgrade path in Emscripten.
Reviewers: sbc100, aheejin
Subscribers: dschuff, jgravelle-google, sunfish, jfb, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D65783
llvm-svn: 370965
Summary:
This change makes it so that passing --shared-memory is all a user
needs to do to get proper multithreaded code. This default can still
be explicitly overridden for any reason using --passive-segments and
--active-segments.
Reviewers: sbc100, quantum
Subscribers: dschuff, jgravelle-google, aheejin, sunfish, jfb, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D64950
llvm-svn: 366504
Summary:
Thread local variables are placed inside a `.tdata` segment. Their symbols are
offsets from the start of the segment. The address of a thread local variable
is computed as `__tls_base` + the offset from the start of the segment.
`.tdata` segment is a passive segment and `memory.init` is used once per thread
to initialize the thread local storage.
`__tls_base` is a wasm global. Since each thread has its own wasm instance,
it is effectively thread local. Currently, `__tls_base` must be initialized
at thread startup, and so cannot be used with dynamic libraries.
`__tls_base` is to be initialized with a new linker-synthesized function,
`__wasm_init_tls`, which takes as an argument a block of memory to use as the
storage for thread locals. It then initializes the block of memory and sets
`__tls_base`. As `__wasm_init_tls` will handle the memory initialization,
the memory does not have to be zeroed.
To help allocating memory for thread-local storage, a new compiler intrinsic
is introduced: `__builtin_wasm_tls_size()`. This instrinsic function returns
the size of the thread-local storage for the current function.
The expected usage is to run something like the following upon thread startup:
__wasm_init_tls(malloc(__builtin_wasm_tls_size()));
Reviewers: tlively, aheejin, kripken, sbc100
Subscribers: dschuff, jgravelle-google, hiraditya, sunfish, jfb, cfe-commits, llvm-commits
Tags: #clang, #llvm
Differential Revision: https://reviews.llvm.org/D64537
llvm-svn: 366272
Summary:
This was causing large addresses to be emitted as negative numbers,
which rightfully caused crashes in binaryen.
Reviewers: aheejin, dschuff
Subscribers: sbc100, jgravelle-google, sunfish, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D64612
llvm-svn: 365930
Summary:
Adds `--passive-segments` and `--active-segments` flags to control
what kind of segments are emitted. For now the default is always
to emit active segments so this is not a breaking change, but in
the future the default will be changed to passive segments when
shared memory is requested and active segments otherwise. When
passive segments are emitted, corresponding memory.init and
data.drop instructions are emitted in a `__wasm_init_memory`
function that is automatically called at the beginning of
`__wasm_call_ctors`.
Reviewers: sbc100, aheejin, dschuff
Subscribers: azakai, dschuff, jgravelle-google, sunfish, jfb, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D59343
llvm-svn: 365088
Sam Clegg