diff options
| -rw-r--r-- | src/cpu.cpp | 12 |
1 files changed, 10 insertions, 2 deletions
diff --git a/src/cpu.cpp b/src/cpu.cpp index 7776821ce..1a878c182 100644 --- a/src/cpu.cpp +++ b/src/cpu.cpp @@ -7,7 +7,7 @@ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>. */ -/** @file cpu.cpp OS/CPU/compiler dependant CPU specific calls. */ +/** @file cpu.cpp OS/CPU/compiler dependent CPU specific calls. */ #include "stdafx.h" #include "core/bitmath_func.hpp" @@ -97,12 +97,20 @@ void ottd_cpuid(int info[4], int type) void ottd_cpuid(int info[4], int type) { #if defined(__i386) && defined(__PIC__) - /* The easy variant would be just cpuid, however... ebx gets clobbered by PIC. */ + /* The easy variant would be just cpuid, however... ebx is being used by the GOT (Global Offset Table) + * in case of PIC; + * clobbering ebx is no alternative: some compiler versions don't like this + * and will issue an error message like + * "can't find a register in class 'BREG' while reloading 'asm'" + */ __asm__ __volatile__ ( "xchgl %%ebx, %1 \n\t" "cpuid \n\t" "xchgl %%ebx, %1 \n\t" : "=a" (info[0]), "=r" (info[1]), "=c" (info[2]), "=d" (info[3]) + /* It is safe to write "=r" for (info[1]) as in case that PIC is enabled for i386, + * the compiler will not choose EBX as target register (but something else). + */ : "a" (type) ); #else |