853111 - Over 7700 lines of warning-spam from selfhosted.out.h, for -Wnarrowing (for converting values >= 128 to 'const char')

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Daniel Holbert [:dholbert]]

Attachment: gzipped dump of warnings

When building mozilla inbound today, I hit ~7700 lines of warning spam along the lines of:
{
 0:31.07 ./selfhosted.out.h:7:70405: warning: narrowing conversion of '203' from 'int' to 'const char' inside { } is ill-formed in C++11 [-Wnarrowing]
 0:31.09 ./selfhosted.out.h:7:70405: warning: narrowing conversion of '185' from 'int' to 'const char' inside { } is ill-formed in C++11 [-Wnarrowing]
 0:31.09 ./selfhosted.out.h:7:70405: warning: narrowing conversion of '236' from 'int' to 'const char' inside { } is ill-formed in C++11 [-Wnarrowing]
 0:31.09 ./selfhosted.out.h:7:70405: warning: narrowing conversion of '184' from 'int' to 'const char' inside { } is ill-formed in C++11 [-Wnarrowing]
}

(These are being spammed for the file "selfhosted.out.h", which is a generated header in $OBJDIR/js/src/, and which indeed has an array of const chars that is initialized with the values quoted above, which are out-of-range for the 'char' type.

I'm tentatively guessing that this is from 
  https://hg.mozilla.org/mozilla-central/rev/b00eb1ef1517
since that was the most recent change to self-hosted stuff, but I'm not sure.

Comment 1

[Daniel Holbert [:dholbert]]

Attachment: selfhosted.out.h (the generated header that causes these warnings)

Comment 2

[Daniel Holbert [:dholbert]]

I'm hitting this using GCC 4.8 from the ubuntu 13.04 "gcc-snapshot" package, BTW. 

I've been using this compiler for at least a week, and I'm pretty sure I haven't seen this build warning before today, but it might be possible that this is a new-in-GCC-4.8 version of this warning for code that's been the same for a while.

Comment 3

[Daniel Holbert [:dholbert]]

hg bisect says this actually started with this cset:
{
changeset:   125577:475c1655ce61
user:        Shu-yu Guo <[e-mail]>
date:        Tue Mar 19 23:26:08 2013 -0700
summary:     Bug 814795 - Remove v8-specific tools for selfhosted code in favor of CPP (r=till)
}

Previous to that, I think the array in selfhosted.out.h only has values below 128. After that changeset, it's got larger values which trigger the massive build-warning-spam.

Comment 4

[Daniel Holbert [:dholbert]]

Attachment: non-spammy selfhosted.out.h (generated from d10ac6c5b14f)

Here's what selfhosted.out.h looks like in a build from d10ac6c5b14f (just before bug 814795's commit).  This one doesn't seem to have values >= 128, as noted above.

Comment 5

[Daniel Holbert [:dholbert]]

Attachment: buggy/spammy selfhosted.out.h (generated from 475c1655ce61)

...and here's the warning-spammy selfhosted.out.h, generated w/ a build from the problematic cset, 475c1655ce61.

Comment 6

[Daniel Holbert [:dholbert]]

(Superficially, it seems that changing this array to have type "unsigned char" instead of "char" would fix this.  Not sure if other things depend on it being "char" though.)

Comment 7

[Daniel Holbert [:dholbert]]

(In reply to Daniel Holbert [:dholbert] from comment #2)
> I'm hitting this using GCC 4.8 from the ubuntu 13.04 "gcc-snapshot" package,
> BTW.

(I just verified that I hit this in GCC 4.7, too -- so this isn't a 4.8-dependant thing.)

Comment 8

[Shu-yu Guo [:shu]]

Attachment: fix

Comment 9

[Till Schneidereit [:till]]

Comment on attachment 727375 [details] [diff] [review]
fix

Review of attachment 727375 [details] [diff] [review]:
-----------------------------------------------------------------

I should have seen that, sorry.

Comment 10

[Shu-yu Guo [:shu]]

(In reply to Till Schneidereit [:till] from comment #9)
> Comment on attachment 727375 [details] [diff] [review]
> fix
> 
> Review of attachment 727375 [details] [diff] [review]:
> -----------------------------------------------------------------
> 
> I should have seen that, sorry.

I should have too, really. :(

Comment 11

[Daniel Holbert [:dholbert]]

No worries - thanks to both of you for the quick action!

Comment 12

[Shu-yu Guo [:shu]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/dee55e5465e5

Comment 13

[Ed Morley [:emorley]]

https://hg.mozilla.org/mozilla-central/rev/dee55e5465e5
https://hg.mozilla.org/mozilla-central/rev/6609ab08172e