Bug 623119

Summary:	__isoc99_sscanf is used regardless of -std option
Product:	[Fedora] Fedora	Reporter:	Stas Sergeev <stsp2>
Component:	glibc	Assignee:	Andreas Schwab <schwab>
Status:	CLOSED NOTABUG	QA Contact:	Fedora Extras Quality Assurance <extras-qa>
Severity:	medium	Docs Contact:
Priority:	low
Version:	13	CC:	fweimer, jakub, schwab
Target Milestone:	---
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2010-08-11 12:09:36 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description Stas Sergeev 2010-08-11 11:42:20 UTC

Description of problem:
All my programs have suddenly started to use
__isoc99_sscanf@@GLIBC_2.7, making it impossible
to run them on an older systems without recompiling.
The changelog of glibc says:
Redirect to __isoc99_* if strict ISO C99 or POSIX
	conformance requested.
But how to "unrequest" that strict conformance,
other than by defining _GNU_SOURCE? -std=gnu89
doesn't help.

Version-Release number of selected component (if applicable):
glibc-2.12-3.x86_64

How reproducible:
Always

Steps to Reproduce:
1. Compile program with sscanf
2. Try to run it on another system with glibc <2.7
  
Actual results:
/lib/libc.so.6: version `GLIBC_2.7' not found

Expected results:
Program works

Additional info:

Comment 1 Jakub Jelinek 2010-08-11 12:09:36 UTC

glibc never pretended to be forward compatible, so if you want to run on system with older glibc, you should compile/link against the oldest glibc you want to support.

To use the non-standard version of sscanf, you need -D_GNU_SOURCE, or e.g. -D_POSIX_C_SOURCE=199506L, as POSIX 2008 mode is now the default.

Comment 2 Stas Sergeev 2010-08-11 12:28:03 UTC

Yes, I understand the forward-compat is
never guaranteed, but is the use of
__isoc99_sscanf really intentional when
-std=gnu89 is used?

Comment 3 Jakub Jelinek 2010-08-11 12:40:20 UTC

Yes.  -std=gnu89 doesn't have very big influence on the content of glibc headers, all it means is that __STRICT_ANSI__ isn't defined.  The Feature Test Macros is what matters.  And, in case of *scanf, it is actually better if the %ac/%as/%a[ GNU extensions are never used any more, and %mc/%ms/%m[ is used instead.  So, the more __isoc99_*scanf is used, the better.