Functions in c++locale.o in libstdc++.a access the errno global int and this is
unsafe for use in threaded programs. Yet another object file in the same
library references the thread-local errno address function. Impact is minimal,
but indicates mixed compilation model object files are linked together into the
same library. This situation occurs on several platforms.
>From of "nm -g /opt/sfw/lib/libstdc++.a" on Solaris 10 (package SFWgcc34l
3.4.2):
/opt/sfw/lib/libstdc++.a[basic_file.o]:
[Index] Value Size Type Bind Other Shndx Name
[38] | 0| 0|NOTY |GLOB |0 |UNDEF |___errno
/opt/sfw/lib/libstdc++.a[c++locale.o]:
[Index] Value Size Type Bind Other Shndx Name
[27] | 0| 0|NOTY |GLOB |0 |UNDEF |errno
On this platform, both should be referencing ___errno.
The same problem appears to exist in libstdc++.so, but it's more difficult to
determine which object the reference comes from.
It's not clear to me how this problem happens at all, as both
basic_file_stdio.cc and c_locale.cc appear to be compiled with the same options
yet obviously were not.
Although the problem occurs on 3.4 libraries, the relevant files (c_locale.cc,
src/Makefile.am) have not to have changed much, so I suspect the problem is
still present.
Platforms I checked:
Solaris 8 SPARC: package SMCgcc342 3.4.2 by Steve Christensen
Solaris 10 x86: package SUNWgccruntime 11.10.0 by Sun
Solaris 10 SPARC: package SFWgcc34l 3.4.2 by Sun
HP-UX 11.11 PA RISC: package GNU_C_C++.GCC_3_4_5 by HP
AIX 5.1: (not sure where this one came from, I'm not an AIX wiz)
Irix 6.5: (not sure where it came from)
Linux RH 9: not a problem, no errno access
Mac OS X: not a problem, no errno access
Impact Analysis: what trouble can this errno access cause?
The functions in c_locale.cc which access errno are templates:
__convert_to_v(const char*, float&, ...)
__convert_to_v(const char*, double&, ...)
__convert_to_v(const char*, long double&, ...)
These parse text and convert it to a floating point value. These in turn are
invoked from templates in locale_facets.tcc:
num_get<_ChartT, _InIter>::do_get(..., float&)
num_get<_ChartT, _InIter>::do_get(..., double&)
num_get<_ChartT, _InIter>::do_get(..., long double&)
money_get<_ChartT, _InIter>::do_get(..., long double&)
locale::facet is used in stream I/O.
Impact: Intermittent failures in multi-threaded applications when converting
floating point numbers from text to a binary value. More specifically, if the
text expresses an out-of-range value (e.g. exponent overflow for a 32-bit
float), an incorrect value may be returned rather than setting failbit.
--
Summary: c++locale.o thread-unsafe in libstdc++
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: craig dot lawson at centrify dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31117
