1196871 - avoid referencing local parameters in LinuxSignal.h

Status: NEW

(Core :: MFBT, defect)

Description

[Nathan Froyd [:froydnj]]

clang doesn't appreciate local parameter references in naked functions.
Rather than hacking around this with preprocessor trickery, let's just
declare all the argument registers as clobbered.  This ensures the
register allocation won't try to use them for loading the handler
address.

fix

Comment 1

[Nathan Froyd [:froydnj]]

Attachment: avoid referencing local parameters in LinuxSignal.h

Things seem to work OK in GCC without referencing the registers in the clobber
specification, but it seemed better to put them there anyway, just to make sure.

Comment 2

[Nathan Froyd [:froydnj]]

We're not going to be able to take this quite yet, since clang miscompiles the code in question.  I've opened a clang bug about it: https://llvm.org/bugs/show_bug.cgi?id=24556

Other options include...writing all the assembly ourselves, I guess.

Comment 3

[Mike Hommey [:glandium]]

preventing inlining sounds like it could work.

Comment 4

[Nathan Froyd [:froydnj]]

(In reply to Mike Hommey [:glandium] from comment #3)
> preventing inlining sounds like it could work.

Nothing gets inlined here.

Comment 5

[Mike Hommey [:glandium]]

(In reply to Nathan Froyd [:froydnj][:nfroyd] from comment #4)
> (In reply to Mike Hommey [:glandium] from comment #3)
> > preventing inlining sounds like it could work.
> 
> Nothing gets inlined here.

The code in the clang bug very much looks inlined.

Comment 6

[Nathan Froyd [:froydnj]]

The generated assembly is for the SignalTrampoline function (I could have made that clearer, my mistake), and there's nothing to be inlined into that.

Comment 7

[BugBot [:suhaib / :marco/ :calixte]]

The bug assignee didn't login in Bugzilla in the last 7 months.
:sg, could you have a look please?
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