[9fans] 5c bug

[9fans] 5c bug

[Steve Simon]

Hi,

I traced a long standing cifs issue to 5c the compiler.

The code in lib9p to validate wstat calls
uses a neat bit of casting which fails when using 5c.

/sys/src/lib9p/srv.c:658-669

These following lines missfire reporting type or qid change
when trying to rename files over cifs.

	if((ushort)~r->d.type){
	...
	if((uchar)~r->d.qid.type || .. ){

but rewriting them like this makes the code work as expected:

	if(r->d.type != (ushort)~0){
	...
	if(r->d.qid.type != (uchar)~0 || ... )

Personally I am happy to hack lib9p but the worry is that
this bug might be affecting other things.

I have no knowledge of the internals of the compilers so
I am afraid I have made no attempt to dig deeper.

-Steve

Re: [9fans] 5c bug

[Charles Forsyth]

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5c shouldn't discard the cast, which implies a mask, but you should also
rewrite the code as you suggest.
(it's not just 5c, since it's the same for several other RISCy ones.)


On Thu, Jul 25, 2019 at 12:20 PM Steve Simon <steve@quintile.net> wrote:

> Hi,
>
> I traced a long standing cifs issue to 5c the compiler.
>
> The code in lib9p to validate wstat calls
> uses a neat bit of casting which fails when using 5c.
>
> /sys/src/lib9p/srv.c:658-669
>
> These following lines missfire reporting type or qid change
> when trying to rename files over cifs.
>
>         if((ushort)~r->d.type){
>         ...
>         if((uchar)~r->d.qid.type || .. ){
>
> but rewriting them like this makes the code work as expected:
>
>         if(r->d.type != (ushort)~0){
>         ...
>         if(r->d.qid.type != (uchar)~0 || ... )
>
> Personally I am happy to hack lib9p but the worry is that
> this bug might be affecting other things.
>
> I have no knowledge of the internals of the compilers so
> I am afraid I have made no attempt to dig deeper.
>
> -Steve
>
>

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