Bug 56088 – cti_vm_throw gets kicked out by gcc 4.6 -flto

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[Bernhard Rosenkraenzer]

Building WebKit with gcc 4.6 with -flto enabled results in a linking error:
/tmp/ccaOGKiM.ltrans0.ltrans.o: In function `ctiVMThrowTrampoline':
ccaOGKiM.ltrans0.o:(.text+0x4c): undefined reference to `cti_vm_throw'

The gcc guys say this is not a bug in gcc, since cti_vm_throw is called only by asm code, it needs to be marked with __attribute__((used))

I can confirm this one failing with LTO with gcc 4.6.1

[Allan Sandfeld Jensen]

Created attachment 130635 [details]
Patch

Add __attribute__((used)) to cti_vm_throw and several other functions that needs it to make linking with -flto work.

[Allan Sandfeld Jensen]

Comment on attachment 130635 [details]
Patch

I am not 100% sure this is the right solution, but without review, I will never be told if I wrong.

[Filip Pizlo]

Comment on attachment 130635 [details]
Patch

This looks fine in principle, but can you rebase your patch?

[Allan Sandfeld Jensen]

Created attachment 143544 [details]
Patch

[Allan Sandfeld Jensen]

Rebased patch. I should not that I have not succeeded in building WebCore with flto yet, but this patch fixes WTF and JavaScriptCore if build separately.

[WebKit Review Bot]

Attachment 143544 [details] did not pass style-queue:

Failed to run "['Tools/Scripts/check-webkit-style', '--diff-files', u'Source/JavaScriptCore/ChangeLog', u'Source..." exit_code: 1
Source/JavaScriptCore/jit/JITStubs.h:466:  cti_vm_throw is incorrectly named. Don't use underscores in your identifier names.  [readability/naming] [4]
Total errors found: 1 in 7 files


If any of these errors are false positives, please file a bug against check-webkit-style.

[Darin Adler]

Comment on attachment 143544 [details]
Patch

I’m not sure about the name FUNCTION_USED.

[Darin Adler]

Comment on attachment 143544 [details]
Patch

Wait, shouldn’t FUNCTION_USED go into Compiler.h instead of Platform.h?

[Allan Sandfeld Jensen]

(In reply to comment #8)
> (From update of attachment 143544 [details])
> I’m not sure about the name FUNCTION_USED.

I am not either, but I don't have a better one. MARK_AS_USED?

(In reply to comment #9)
> Wait, shouldn’t FUNCTION_USED go into Compiler.h instead of Platform.h?

I originally placed it Platform.h because it was were JSC_HOST_CALL was defined which is another flag for JIT-assembler functions, but they may both be misplaced.

[Allan Sandfeld Jensen]

Created attachment 143584 [details]
Patch

Renamed FUNCTION_USED to REFERENCED_FROM_ASM and moved its definition to Compiler.h

[WebKit Review Bot]

Comment on attachment 143584 [details]
Patch

Clearing flags on attachment: 143584

Committed r118344: <http://trac.webkit.org/changeset/118344>

[WebKit Review Bot]

All reviewed patches have been landed.  Closing bug.