From 0909c8c2d547e45ca50e2492b08ec93a37b35237 Mon Sep 17 00:00:00 2001 From: Benjamin Herrenschmidt Date: Fri, 20 Oct 2006 11:47:18 +1000 Subject: [POWERPC] Support feature fixups in vdso's This patch reworks the feature fixup mecanism so vdso's can be fixed up. The main issue was that the construct: .long label (or .llong on 64 bits) will not work in the case of a shared library like the vdso. It will generate an empty placeholder in the fixup table along with a reloc, which is not something we can deal with in the vdso. The idea here (thanks Alan Modra !) is to instead use something like: 1: .long label - 1b That is, the feature fixup tables no longer contain addresses of bits of code to patch, but offsets of such code from the fixup table entry itself. That is properly resolved by ld when building the .so's. I've modified the fixup mecanism generically to use that method for the rest of the kernel as well. Another trick is that the 32 bits vDSO included in the 64 bits kernel need to have a table in the 64 bits format. However, gas does not support 32 bits code with a statement of the form: .llong label - 1b (Or even just .llong label) That is, it cannot emit the right fixup/relocation for the linker to use to assign a 32 bits address to an .llong field. Thus, in the specific case of the 32 bits vdso built as part of the 64 bits kernel, we are using a modified macro that generates: .long 0xffffffff .llong label - 1b Note that is assumes that the value is negative which is enforced by the .lds (those offsets are always negative as the .text is always before the fixup table and gas doesn't support emiting the reloc the other way around). Signed-off-by: Benjamin Herrenschmidt Signed-off-by: Paul Mackerras --- include/asm-powerpc/timex.h | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) (limited to 'include/asm-powerpc/timex.h') diff --git a/include/asm-powerpc/timex.h b/include/asm-powerpc/timex.h index 3b9a8e78680..e3f08cf9148 100644 --- a/include/asm-powerpc/timex.h +++ b/include/asm-powerpc/timex.h @@ -30,13 +30,15 @@ static inline cycles_t get_cycles(void) ret = 0; __asm__ __volatile__( - "98: mftb %0\n" + "97: mftb %0\n" "99:\n" ".section __ftr_fixup,\"a\"\n" + ".align 2\n" + "98:\n" " .long %1\n" " .long 0\n" - " .long 98b\n" - " .long 99b\n" + " .long 97b-98b\n" + " .long 99b-98b\n" ".previous" : "=r" (ret) : "i" (CPU_FTR_601)); #endif -- cgit v1.2.3 From 859deea949c382d9ccb6397fe33df3703ecef45d Mon Sep 17 00:00:00 2001 From: Benjamin Herrenschmidt Date: Fri, 20 Oct 2006 14:37:05 +1000 Subject: [POWERPC] Cell timebase bug workaround The Cell CPU timebase has an erratum. When reading the entire 64 bits of the timebase with one mftb instruction, there is a handful of cycles window during which one might read a value with the low order 32 bits already reset to 0x00000000 but the high order bits not yet incremeted by one. This fixes it by reading the timebase again until the low order 32 bits is no longer 0. That might introduce occasional latencies if hitting mftb just at the wrong time, but no more than 70ns on a cell blade, and that was considered acceptable. Signed-off-by: Benjamin Herrenschmidt Acked-by: Olof Johansson Signed-off-by: Paul Mackerras --- include/asm-powerpc/timex.h | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-) (limited to 'include/asm-powerpc/timex.h') diff --git a/include/asm-powerpc/timex.h b/include/asm-powerpc/timex.h index e3f08cf9148..92dedde761d 100644 --- a/include/asm-powerpc/timex.h +++ b/include/asm-powerpc/timex.h @@ -8,6 +8,7 @@ */ #include +#include #define CLOCK_TICK_RATE 1024000 /* Underlying HZ */ @@ -15,13 +16,11 @@ typedef unsigned long cycles_t; static inline cycles_t get_cycles(void) { - cycles_t ret; - #ifdef __powerpc64__ - - __asm__ __volatile__("mftb %0" : "=r" (ret) : ); - + return mftb(); #else + cycles_t ret; + /* * For the "cycle" counter we use the timebase lower half. * Currently only used on SMP. @@ -41,9 +40,8 @@ static inline cycles_t get_cycles(void) " .long 99b-98b\n" ".previous" : "=r" (ret) : "i" (CPU_FTR_601)); -#endif - return ret; +#endif } #endif /* __KERNEL__ */ -- cgit v1.2.3