http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59782
Bug ID: 59782 Summary: libcpp does not avoid bug #48326 when compiled by older GCC Product: gcc Version: 4.8.2 Status: UNCONFIRMED Severity: normal Priority: P3 Component: preprocessor Assignee: unassigned at gcc dot gnu.org Reporter: michael at talosis dot ca GCC 4.7.0 and other older versions have a bug (#48326) where the target attribute can leak, causing illegal instructions to be emitted in code intended to be generic. GCC 4.6.0 through 4.8.2 also contain code that triggers this bug, in libcpp/lex.c. That file uses the target attribute to opportunistically use MMX/SSE even in a generic binary. The result is that bootstrap is blocked if starting from 4.7.0 when the actual CPU does not support the new instructions. Currently the problem block of code is preprocessed in if GCC 4.5.0 or later is detected. It should instead only be used for 4.7.1 or later. Note that it is somewhat important to also fix this in 4.7.4. This bug only bites when upgrading from an old GCC. If someone has an old GCC with C++ not installed, then they cannot move directly to 4.8.x, and will have to build 4.7.x as an intermediate.