| Message ID | CAFULd4Ze8=Y5vB7oqcOvHZfpu8B9nY4kA1jXMT4hmOsuZoqrtQ@mail.gmail.com |
|---|---|
| State | New |
| Headers | show |
On Thu, Oct 16, 2014 at 11:19:49AM +0200, Uros Bizjak wrote: > Hello! > > Now that %ebx is also allocatable in PIC modes, we can cleanup > config/i386/cpuid considerably. I propose to remove all PIC related > specializations of __cpuid and __cpuid_count and protect the > compilation with "#if __GNUC__ >= 5". > > The only drawback would be that non-bootstrapped build with gcc < 5.0 > will ignore -march=native, but I think this should be acceptable. I'm worried about that. Can't you instead keep the current cpuid.h stuff as is, just add && __GNUC__ < 5 to that, so it treats GCC 5+ PIC as if __PIC__ wasn't defined? Or, at least use cpuid.h even for older GCC if __PIC__ is not defined (or __x86_64__ is defined and not medium/large PIC model)? Jakub
On Thu, Oct 16, 2014 at 11:24 AM, Jakub Jelinek <jakub@redhat.com> wrote: >> Now that %ebx is also allocatable in PIC modes, we can cleanup >> config/i386/cpuid considerably. I propose to remove all PIC related >> specializations of __cpuid and __cpuid_count and protect the >> compilation with "#if __GNUC__ >= 5". >> >> The only drawback would be that non-bootstrapped build with gcc < 5.0 >> will ignore -march=native, but I think this should be acceptable. > > I'm worried about that. > Can't you instead keep the current cpuid.h stuff as is, just add > && __GNUC__ < 5 > to that, so it treats GCC 5+ PIC as if __PIC__ wasn't defined? > > Or, at least use cpuid.h even for older GCC if __PIC__ is not defined > (or __x86_64__ is defined and not medium/large PIC model)? Do we really care that much about non-bootstrapped build? I don't see a compelling reason to keep these definitions, and by moving version to 5.0, it seems like the right time to cut the questionable compatibility stuff out. Uros.
On Thu, Oct 16, 2014 at 11:28:20AM +0200, Uros Bizjak wrote: > On Thu, Oct 16, 2014 at 11:24 AM, Jakub Jelinek <jakub@redhat.com> wrote: > > >> Now that %ebx is also allocatable in PIC modes, we can cleanup > >> config/i386/cpuid considerably. I propose to remove all PIC related > >> specializations of __cpuid and __cpuid_count and protect the > >> compilation with "#if __GNUC__ >= 5". > >> > >> The only drawback would be that non-bootstrapped build with gcc < 5.0 > >> will ignore -march=native, but I think this should be acceptable. > > > > I'm worried about that. > > Can't you instead keep the current cpuid.h stuff as is, just add > > && __GNUC__ < 5 > > to that, so it treats GCC 5+ PIC as if __PIC__ wasn't defined? > > > > Or, at least use cpuid.h even for older GCC if __PIC__ is not defined > > (or __x86_64__ is defined and not medium/large PIC model)? > > Do we really care that much about non-bootstrapped build? I don't see At least on Linux, driver-i386.c should not be built with PIC normally, so at least changing #if __GNUC__ >= 5 to #if defined(__GNUC__) && (__GNUC__ >= 5 || !defined(__PIC__)) would limit the -march=native change for non-bootstrapped compilers to Darwin only (or what other targets use PIC by default?). Jakub
On Thu, Oct 16, 2014 at 11:36 AM, Jakub Jelinek <jakub@redhat.com> wrote: >> >> Now that %ebx is also allocatable in PIC modes, we can cleanup >> >> config/i386/cpuid considerably. I propose to remove all PIC related >> >> specializations of __cpuid and __cpuid_count and protect the >> >> compilation with "#if __GNUC__ >= 5". >> >> >> >> The only drawback would be that non-bootstrapped build with gcc < 5.0 >> >> will ignore -march=native, but I think this should be acceptable. >> > >> > I'm worried about that. >> > Can't you instead keep the current cpuid.h stuff as is, just add >> > && __GNUC__ < 5 >> > to that, so it treats GCC 5+ PIC as if __PIC__ wasn't defined? >> > >> > Or, at least use cpuid.h even for older GCC if __PIC__ is not defined >> > (or __x86_64__ is defined and not medium/large PIC model)? >> >> Do we really care that much about non-bootstrapped build? I don't see > > At least on Linux, driver-i386.c should not be built with PIC normally, > so at least changing > #if __GNUC__ >= 5 > to > #if defined(__GNUC__) && (__GNUC__ >= 5 || !defined(__PIC__)) > would limit the -march=native change for non-bootstrapped compilers to > Darwin only (or what other targets use PIC by default?). Yes, this would work for me - the goal is to keep only one "universal" __cpuid (and __cpuid_count) define, and the above condition fits this goal. Uros.
Index: config/i386/cpuid.h =================================================================== --- config/i386/cpuid.h (revision 216282) +++ config/i386/cpuid.h (working copy) @@ -146,56 +146,7 @@ #define signature_VORTEX_ecx 0x436f5320 #define signature_VORTEX_edx 0x36387865 -#if defined(__i386__) && defined(__PIC__) -/* %ebx may be the PIC register. */ -#if __GNUC__ >= 3 #define __cpuid(level, a, b, c, d) \ - __asm__ ("xchg{l}\t{%%}ebx, %k1\n\t" \ - "cpuid\n\t" \ - "xchg{l}\t{%%}ebx, %k1\n\t" \ - : "=a" (a), "=&r" (b), "=c" (c), "=d" (d) \ - : "0" (level)) - -#define __cpuid_count(level, count, a, b, c, d) \ - __asm__ ("xchg{l}\t{%%}ebx, %k1\n\t" \ - "cpuid\n\t" \ - "xchg{l}\t{%%}ebx, %k1\n\t" \ - : "=a" (a), "=&r" (b), "=c" (c), "=d" (d) \ - : "0" (level), "2" (count)) -#else -/* Host GCCs older than 3.0 weren't supporting Intel asm syntax - nor alternatives in i386 code. */ -#define __cpuid(level, a, b, c, d) \ - __asm__ ("xchgl\t%%ebx, %k1\n\t" \ - "cpuid\n\t" \ - "xchgl\t%%ebx, %k1\n\t" \ - : "=a" (a), "=&r" (b), "=c" (c), "=d" (d) \ - : "0" (level)) - -#define __cpuid_count(level, count, a, b, c, d) \ - __asm__ ("xchgl\t%%ebx, %k1\n\t" \ - "cpuid\n\t" \ - "xchgl\t%%ebx, %k1\n\t" \ - : "=a" (a), "=&r" (b), "=c" (c), "=d" (d) \ - : "0" (level), "2" (count)) -#endif -#elif defined(__x86_64__) && (defined(__code_model_medium__) || defined(__code_model_large__)) && defined(__PIC__) -/* %rbx may be the PIC register. */ -#define __cpuid(level, a, b, c, d) \ - __asm__ ("xchg{q}\t{%%}rbx, %q1\n\t" \ - "cpuid\n\t" \ - "xchg{q}\t{%%}rbx, %q1\n\t" \ - : "=a" (a), "=&r" (b), "=c" (c), "=d" (d) \ - : "0" (level)) - -#define __cpuid_count(level, count, a, b, c, d) \ - __asm__ ("xchg{q}\t{%%}rbx, %q1\n\t" \ - "cpuid\n\t" \ - "xchg{q}\t{%%}rbx, %q1\n\t" \ - : "=a" (a), "=&r" (b), "=c" (c), "=d" (d) \ - : "0" (level), "2" (count)) -#else -#define __cpuid(level, a, b, c, d) \ __asm__ ("cpuid\n\t" \ : "=a" (a), "=b" (b), "=c" (c), "=d" (d) \ : "0" (level)) @@ -204,8 +155,8 @@ __asm__ ("cpuid\n\t" \ : "=a" (a), "=b" (b), "=c" (c), "=d" (d) \ : "0" (level), "2" (count)) -#endif + /* Return highest supported input value for cpuid instruction. ext can be either 0x0 or 0x8000000 to return highest supported value for basic or extended cpuid information. Function returns 0 if cpuid Index: config/i386/driver-i386.c =================================================================== --- config/i386/driver-i386.c (revision 216282) +++ config/i386/driver-i386.c (working copy) @@ -24,7 +24,7 @@ along with GCC; see the file COPYING3. If not see const char *host_detect_local_cpu (int argc, const char **argv); -#ifdef __GNUC__ +#if __GNUC__ >= 5 #include "cpuid.h" struct cache_desc @@ -942,9 +942,10 @@ done: } #else -/* If we aren't compiling with GCC then the driver will just ignore - -march and -mtune "native" target and will leave to the newly - built compiler to generate code for its default target. */ +/* If we aren't compiling with GCC that is able to handle %EBX + register in PIC and non-PIC modes, then the driver will just + ignore -march and -mtune "native" target and will leave to the + newly built compiler to generate code for its default target. */ const char *host_detect_local_cpu (int, const char **) {
Hello! Now that %ebx is also allocatable in PIC modes, we can cleanup config/i386/cpuid considerably. I propose to remove all PIC related specializations of __cpuid and __cpuid_count and protect the compilation with "#if __GNUC__ >= 5". The only drawback would be that non-bootstrapped build with gcc < 5.0 will ignore -march=native, but I think this should be acceptable. Bootstrapped build will still work as expected. 2014-10-16 Uros Bizjak <ubizjak@gmail.com> * config/i386/cpuid.h (__cpuid): Remove definitions that handle %ebx register in a special way. (__cpuid_count): Ditto. * config/i386/driver-i386.h: Protect with #if __GNUC__ >= 5. (host_detect_local_cpu): Mention that GCC that is able to handle %ebx register in PIC and non-PIC modes is required to compile the function. Bootstrapped and regression tested on x86_64-linux-gnu {,-m32}. Any comments? Uros.