Bug 1084639

Summary:	GCC 8: libX11 build fails
Product:	[openSUSE] openSUSE Tumbleweed	Reporter:	Martin Liška <martin.liska>
Component:	X.Org	Assignee:	Michal Srb <msrb>
Status:	RESOLVED FIXED	QA Contact:	E-mail List <xorg-maintainer-bugs>
Severity:	Normal
Priority:	P5 - None	CC:	msrb, sndirsch
Version:	Current
Target Milestone:	---
Hardware:	Other
OS:	Other
Whiteboard:
Found By:	---	Services Priority:
Business Priority:		Blocker:	---
Marketing QA Status:	---	IT Deployment:	---
Bug Depends on:
Bug Blocks:	1084649
Attachments:	Use flexible array member instead of fake size.

Description Martin Liška 2018-03-09 10:04:07 UTC

Build the package with GCC 8, there's error:

[  108s] /usr/include/bits/string_fortified.h:90:10: error: '__builtin_strcpy' forming offset 2 is out of the bounds [0, 1] [-Werror=array-bounds]

Please build the project as follows to reproduce the issue:
osc build --alternative-project=openSUSE:Factory:Staging:Gcc7

Comment 1 Michal Srb 2018-03-15 07:56:33 UTC

Confirmed. The full error is:

> In file included from /usr/include/string.h:494,
>                  from /usr/include/X11/Xos.h:62,
>                  from imLcIm.c:42:
> In function 'strcpy',
>     inlined from '_XimWriteCachedDefaultTree' at imLcIm.c:479:5,
>     inlined from '_XimCreateDefaultTree' at imLcIm.c:616:2,
>     inlined from '_XimLocalOpenIM' at imLcIm.c:700:5:
> /usr/include/bits/string_fortified.h:90:10: error: '__builtin_strcpy'
> forming offset 2 is out of the bounds [0, 1] [-Werror=array-bounds]
>    return __builtin___strcpy_chk (__dest, __src, __bos (__dest));

The offending line is:

> imLcIm.c:479:  strcpy (m->fname+strlen(name)+1, encoding);

The `m` is `struct _XimCacheStruct*` and the `fname` field is `char fname[1]`.

So gcc is complaining that we are going to write past this 1-element array. The  allocated memory for `m` is actually big enough to store the full fname plus encoding behind the `_XimCacheStruct` struct, so it works.

No idea why the original author decided that `char fname[1]` is a good way to declare it. I'll change it to something that doesn't trigger the warning.

Comment 2 Michal Srb 2018-03-15 08:53:50 UTC

Created attachment 763761 [details]
Use flexible array member instead of fake size.

Fix for the build error. Also sent to xorg-devel:
https://lists.x.org/archives/xorg-devel/2018-March/056312.html

Comment 3 Stefan Dirsch 2018-03-15 10:55:25 UTC

Thanks, Michal! Could you do a SR for X11:XOrg/libX11, so we can close the bugreport?

Comment 4 Stefan Dirsch 2018-03-15 11:02:53 UTC

(In reply to Stefan Dirsch from comment #3)
> Thanks, Michal! Could you do a SR for X11:XOrg/libX11, so we can close the
> bugreport?

OMG. It was already queued. Thanks!