llvm dev - Jun 2018 - [WebAssembly] lld dynamic loader

Hello,

The table generated by lld (Wasm target) have a max size.

So this make impossible to add some others functions in the table .

As for the moment only one Table is available in WAsm this is the only way
to add function in a dynamic way.



Having a none static size of the table is useful for a kind dynamic
loader/inker at run-time: by adding some exported functions coming from
another modules in the table, so call_indirect can call dynamically some
function coming from another wasm module.



So I am wondering if the static size of the table have a specific goal ?

If not did you think the WASM_LIMITS_FLAG_HAS_MAX can be remove ?



https://llvm.org/svn/llvm-project/lld/trunk/wasm/Writer.cpp

 void Writer::createTableSection() {

..

WasmLimits Limits = {WASM_LIMITS_FLAG_HAS_MAX, TableSize, TableSize};





Thks in advance,

Ghis
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Hi Ghis

Originally when we wrote the wasm port of lld we didn't support
importing or exporting the table so it made sense to set a max size.
However, now that we have the --import-table flag I don't see why we
shouldn't support tables without a max size.  Feel free to send a
patch, or open a bug and I will get around to it.

cheers,
sam

On Fri, Jun 1, 2018 at 6:00 AM, HUDE Ghislain via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Hello,
>
> The table generated by lld (Wasm target) have a max size.
>
> So this make impossible to add some others functions in the table .
>
> As for the moment only one Table is available in WAsm this is the only way
> to add function in a dynamic way.
>
>
>
> Having a none static size of the table is useful for a kind dynamic
> loader/inker at run-time: by adding some exported functions coming from
> another modules in the table, so call_indirect can call dynamically some
> function coming from another wasm module.
>
>
>
> So I am wondering if the static size of the table have a specific goal ?
>
> If not did you think the WASM_LIMITS_FLAG_HAS_MAX can be remove ?
>
>
>
> https://llvm.org/svn/llvm-project/lld/trunk/wasm/Writer.cpp
>
>  void Writer::createTableSection() {
>
> ..
>
> WasmLimits Limits = {WASM_LIMITS_FLAG_HAS_MAX, TableSize, TableSize};
>
>
>
>
>
> Thks in advance,
>
> Ghis
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>

Hi Sam,
Thanks for your answer!

Sorry I didn't really know how to process, but this issue block me to make
some legacy C code works without having some glue with a bit static lib ;(

(The change have really low risk)
The changes I used locally to make dlopen/dlclose et dlsym mechanism works
:) :
Index: wasm/Writer.cpp
==================================================================---
wasm/Writer.cpp     (revision 330555)
+++ wasm/Writer.cpp     (working copy)
@@ -257,7 +257,7 @@
   raw_ostream &OS = Section->getStream();

   writeUleb128(OS, 1, "table count");
-  WasmLimits Limits = {WASM_LIMITS_FLAG_HAS_MAX, TableSize, TableSize};
+  WasmLimits Limits = {0, TableSize, TableSize};
   writeTableType(OS, WasmTable{WASM_TYPE_ANYFUNC, Limits});
 }

May be to have a code more readable   WASM_LIMITS_FLAG_HAS_NO_MAX (=0) can
be added.

Thks,
Ghis


2018-06-03 23:45 GMT+02:00 Sam Clegg <sbc at google.com>:
> Hi Ghis
>
> Originally when we wrote the wasm port of lld we didn't support
> importing or exporting the table so it made sense to set a max size.
> However, now that we have the --import-table flag I don't see why we
> shouldn't support tables without a max size.  Feel free to send a
> patch, or open a bug and I will get around to it.
>
> cheers,
> sam
>
> On Fri, Jun 1, 2018 at 6:00 AM, HUDE Ghislain via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> > Hello,
> >
> > The table generated by lld (Wasm target) have a max size.
> >
> > So this make impossible to add some others functions in the table .
> >
> > As for the moment only one Table is available in WAsm this is the only
> way
> > to add function in a dynamic way.
> >
> >
> >
> > Having a none static size of the table is useful for a kind dynamic
> > loader/inker at run-time: by adding some exported functions coming
from
> > another modules in the table, so call_indirect can call dynamically
some
> > function coming from another wasm module.
> >
> >
> >
> > So I am wondering if the static size of the table have a specific goal
?
> >
> > If not did you think the WASM_LIMITS_FLAG_HAS_MAX can be remove ?
> >
> >
> >
> > https://llvm.org/svn/llvm-project/lld/trunk/wasm/Writer.cpp
> >
> >  void Writer::createTableSection() {
> >
> > ..
> >
> > WasmLimits Limits = {WASM_LIMITS_FLAG_HAS_MAX, TableSize, TableSize};
> >
> >
> >
> >
> >
> > Thks in advance,
> >
> > Ghis
> >
> >
> >
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >
>
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