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(svn r26225) -Document: more tidbits about cpuid and PIC (Eagle_Rainbow)

release/1.4
rubidium 2014-01-04 19:46:24 +00:00
parent b48bb25288
commit 4575420dcc
1 changed files with 10 additions and 2 deletions
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12
src/cpu.cpp
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@ -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/>. * 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 "stdafx.h"
#include "core/bitmath_func.hpp" #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) void ottd_cpuid(int info[4], int type)
{ {
#if defined(__i386) && defined(__PIC__) #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__ ( __asm__ __volatile__ (
"xchgl %%ebx, %1 \n\t" "xchgl %%ebx, %1 \n\t"
"cpuid \n\t" "cpuid \n\t"
"xchgl %%ebx, %1 \n\t" "xchgl %%ebx, %1 \n\t"
: "=a" (info[0]), "=r" (info[1]), "=c" (info[2]), "=d" (info[3]) : "=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) : "a" (type)
); );
#else #else