I intend to slowly upgrade all alignments to the Align type in lld as well.
Some places talk about alignment in Bytes while other specify them as Log2(Bytes).
Let's make sure all of this is coherent.
Differential Revision: https://reviews.llvm.org/D139181
This adds an `--export-memory` option to wasm-ld which allows passing
a name to give to the exported memory, and extends `--import-memory` to
allow passing a <module>,<name> pair specifying where the memory should
be imported from.
This is based on https://reviews.llvm.org/D131376, with the main
difference being that it only supports exporting memory by one name.
Differential Revision: https://reviews.llvm.org/D135898
Add some checks around this combination of flags
Also, honor `--global-base` when specified in `--stack-first` mode
rather than ignoring it. But error out if the specified base preseeds
the end of the stack.
Differential Revision: https://reviews.llvm.org/D136117
Define a `__heap_end` symbol that marks the end of the memory region
that starts at `__heap_base`. This will allow malloc implementations to
know how much memory they can use at `__heap_base` even if someone has
done a `memory.grow` before they can initialize their state.
Differential Revision: https://reviews.llvm.org/D136110
This flag acts just like the existing `--features` flag but instead
of replacing the set of inferred features it adds to it.
This is useful for example if you want to `--export` a mutable global
but none of the input of object were built with mutable global support.
In that case you can do `--extra-features=mutable-globals` to avoid the
linker error that would otherwise be generated in this case:
wasm-ld: error: mutable global exported but 'mutable-globals' feature not present in inputs: `__stack_pointer`. Use --no-check-features to suppress.
Differential Revision: https://reviews.llvm.org/D135831
The ELF backend originally used `getSymbols()` but went though a
sequence of changes that resulted in this method being called
`symbols()`.
d8f8abbd4a replaced `getSymbols()` with
`forEachSymbol`.
a2fc964417 replaced `forEachSymbol` with
`llvm::iterator_range`.
e9262edf0d replaced `llvm::iterator_range`
with `symbols()`.
Differential Revision: https://reviews.llvm.org/D131284
Instead, export `__wasm_apply_data_relocs` and `__wasm_call_ctors`
separately.
This is required since user code in a shared library (such as static
constructors) should not be run until relocations have been applied to
all loaded libraries.
See: https://github.com/emscripten-core/emscripten/issues/17295
Differential Revision: https://reviews.llvm.org/D128515
It turns out we were already allocating static address space for TLS
data along with the non-TLS static data, but this space was going
unused/ignored.
With this change, we include the TLS segment in `__wasm_init_memory`
(which does the work of loading the passive segments into memory when a
module is first loaded). We also set the `__tls_base` global to point
to the start of this segment.
This means that the runtime can use this static copy of the TLS data for
the first/primary thread if it chooses, rather than doing a runtime
allocation prior to calling `__wasm_init_tls`.
Practically speaking, this will allow emscripten to avoid dynamic
allocation of TLS region on the main thread.
Differential Revision: https://reviews.llvm.org/D126107
In programs that don't otherwise depend on `__tls_base` it won't
be marked as live. However this symbol is used internally in
a couple of places do we need to mark it as live explictily in
those places.
Fixes: #54386
Differential Revision: https://reviews.llvm.org/D121931
In particular we use these in two places:
1. When building PIC code we no longer need to combine output segments
into a single segment that can be initialized at `__memory_base`.
Instead each segment can encode its offset from `__memory_base` in
its initializer. e.g.
```
(i32.add (global.get __memory_base) (i32.const offset)
```
2. When building PIC code we no longer need to relocation internalized
global addresses. We can just initialize them with their correct
offsets.
Differential Revision: https://reviews.llvm.org/D121420
This is a new mode for handling unresolved symbols that allows all
symbols to be imported in the same that they would be in the case of
`-fpie` or `-shared`, but generting an otherwise fixed/non-relocatable
binary.
Code linked in this way should still be compiled with `-fPIC` so that
data symbols can be resolved via imports.
This essentially allows the building of static binaries that have
dynamic imports. See:
https://github.com/emscripten-core/emscripten/issues/12682
As with other uses of the experimental dynamic linking ABI, this
behaviour will produce a warning unless run with `--experimental-pic`.
Differential Revision: https://reviews.llvm.org/D91577
We already perform memory initialization and apply global relocations
during start. It makes sense to performs data relocations too. I think
the reason we were not doing this already is solely historical.
Differential Revision: https://reviews.llvm.org/D117412
Move all variables at file-scope or function-static-scope into a hosting structure (lld::CommonLinkerContext) that lives at lldMain()-scope. Drivers will inherit from this structure and add their own global state, in the same way as for the existing COFFLinkerContext.
See discussion in https://lists.llvm.org/pipermail/llvm-dev/2021-June/151184.html
Differential Revision: https://reviews.llvm.org/D108850
Previously relocations were only generated for PIC output, but
relocations for TLS GOT entries are always needed when shared
memory is enabled, not just in PIC mode.
This means that the `__wasm_apply_global_tls_relocs` is now
generated even for statically linked (non-PIC) output. Without
this the globals that hold the addresses of TLS symbols are
not set correctly.
Differential Revision: https://reviews.llvm.org/D112833
Previously we were relying on the dynamic loader to take care of this
but it simple and correct for us to do it here instead.
Now we initialize bss segments as part of `__wasm_init_memory` at the
same time we initialize passive segments.
In addition we extent the us of `__wasm_init_memory` outside of shared
memory situations. Specifically it is now used to initialize bss
segments when the memory is imported.
Differential Revision: https://reviews.llvm.org/D112667
We previously had a limitation that TLS variables could not
be exported (and therefore could also not be imported). This
change removed that limitation.
Differential Revision: https://reviews.llvm.org/D108877
For multithreaded modules (i.e. modules with a shared memory), lld injects a
synthetic Wasm start function that is automatically called during instantiation
to initialize memory from passive data segments. Even though the module will be
instantiated separately on each thread, memory initialization should happen only
once. Furthermore, memory initialization should be finished by the time each
thread finishes instantiation. Since multiple threads may be instantiating their
modules at the same time, the synthetic function must synchronize them.
The current synchronization tries to atomically increment a flag from 0 to 1 in
memory then enters one of two cases. First, if the increment was successful, the
current thread is responsible for initializing memory. It does so, increments
the flag to 2 to signify that memory has been initialized, then notifies all
threads waiting on the flag. Otherwise, the thread atomically waits on the flag
with an expected value of 1 until memory has been initialized. Either the
initializer thread finishes initializing memory (i.e. sets the flag to 2) first
and the waiter threads do not end up blocking, or the waiter threads succesfully
start waiting before memory is initialized so they will be woken by the
initializer thread once it has finished.
One complication with this scheme is that there are various contexts on the Web,
most notably on the main browser thread, that cannot successfully execute a
wait. Executing a wait in these contexts causes a trap, and in this case would
cause instantiation to fail. The embedder must therefore ensure that these
contexts win the race and become responsible for initializing memory, since that
is the only code path that does not execute a wait.
Unfortunately, since only one thread can win the race and initialize memory,
this scheme makes it impossible to have multiple threads in contexts that cannot
wait. For example, it is not currently possible to instantiate the module on
both the main browser thread as well as in an AudioWorklet. To loosen this
restriction, this commit inserts an extra check so that the wait will not be
executed at all when memory has already been initialized, i.e. when the flag
value is 2. After this change, the module can be instantiated on threads in
non-waiting contexts as long as the embedder can guarantee either that the
thread will win the race and initialize memory (as before) or that memory has
already been initialized when instantiation begins. Threads in contexts that can
wait can continue racing to initialize memory.
Fixes (or at least improves) PR51702.
Reviewed By: dschuff
Differential Revision: https://reviews.llvm.org/D109722
Remove some unnecessary logging from wasm-ld when running under
`--verbose`. Unlike `-debug` this logging is available in release
builds. This change makes it little more minimal/readable.
Also, avoid compiling the `debugWrite` function in releaase builds
where it does nothing. This should remove a lot debug strings from
the binary, and avoid having to construct unused debug strings at
runtime.
Differential Revision: https://reviews.llvm.org/D109583
In the case that TLS is used in the single-threaded program, and
therefore effectively lowered away, we still optionally create a
`__tls_base` symbols, but the code for setting it was assuming it was
always created.
Differential Revision: https://reviews.llvm.org/D109518
In the case of weakly defined symbols in shared libraries we now
generate both an import and an export. The dynamic linker can then
choose how a winner from among all the shared libraries that define a
given symbol.
Previously any direct usage of a weakly defined symbol would use the
DSO-local definition (For example, even through there would be single
address for a weakly defined function, each DSO could end up directly
calling its local version).
Fixes: https://github.com/emscripten-core/emscripten/issues/13773
Differential Revision: https://reviews.llvm.org/D108413
In PIC mode we import function address via `GOT.mem` imports but for
direct function calls we still import the first class function.
However, if the function is never directly called we can avoid the first
class import completely.
Differential Revision: https://reviews.llvm.org/D108345
__heap_base was not aligned. In practice, it will often be aligned
simply because it follows the stack, but when the stack is placed at the
beginning (with the --stack-first option), the __heap_base might be
unaligned. It could even be byte-aligned.
At least wasi-libc appears to expect that __heap_base is aligned:
659ff41456/dlmalloc/src/malloc.c (L5224)
While WebAssembly itself does not appear to require any alignment for
memory accesses, it is sometimes required when sharing a pointer
externally. For example, WASI might expect alignment up to 8:
https://github.com/WebAssembly/WASI/blob/main/phases/snapshot/docs.md#-timestamp-u64
This issue got introduced with the addition of the --stack-first flag:
https://reviews.llvm.org/D46141
I suspect the lack of alignment wasn't intentional here.
Differential Revision: https://reviews.llvm.org/D106499
This avoids duplication and simplifies the code in several places
without increasing the size of the symbol union (at least not
above the assert'd limit of 120 bytes).
Originally commit: 9b965b37c7
Reverted in: 16aac493e5.
Differential Revision: https://reviews.llvm.org/D106026
This avoids duplication and simplifies the code in several places
without increasing the size of the symbol union (at least not
above the assert'd limit of 120 bytes).
Differential Revision: https://reviews.llvm.org/D106026
Guillaume Chatelet