| Message ID | 1463659895-16281-1-git-send-email-talha_imran@mentor.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, May 19, 2016 at 05:11:35PM +0500, Talha Imran wrote: > With specification at hand from the reference manual from Freescale > http://cache.nxp.com/files/32bit/doc/ref_manual/SPEPEM.pdf , I have found a fix > to efscmp* instructions handling in QEMU. > > efscmp* instructions in QEMU set crD (Condition Register nibble) values as > (0b0100 << 2) = 0b10000 (consider the HELPER_SINGLE_SPE_CMP macro which left > shifts the value returned by efscmp* handler by 2 bits). A value of 0b10000 is > not correct according the to the reference manual. > > The reference manual expects efscmp* instructions to return a value of 0bx1xx. > Please find attached a patch which disables left shifting in > HELPER_SINGLE_SPE_CMP macro. This macro is used by efscmp* and efstst* > instructions only. efstst* instruction handlers, in turn, call efscmp* handlers > too. > > *Explanation:* > Traditionally, each crD (condition register nibble) consist of 4 bits, which is > set by comparisons as follows: > crD = W X Y Z > where > W = Less than > X = Greater than > Y = Equal to > > However, efscmp* instructions being a special case return a binary result. > (efscmpeq will set the crD = 0bx1xx iff when op1 == op2 and 0bx0xx otherwise; > i.e. there is no notion of different crD values based on Less than, Greater > than and Equal to). > > This effectively means that crD will store a "Greater than" comparison result > iff efscmp* instruction comparison is TRUE. Compiler exploits this feature by > checking for "Branch if Less than or Equal to" (ble instruction) OR "Branch if > Greater than" (bgt instruction) for Branch if FALSE OR Branch if TRUE > respectively after an efscmp* instruction. This can be seen in a assembly code > snippet below: > > 27 if (__real__ x != 3.0f || __imag__ x != 4.0f) > 10000498: lwz r10,8(r31) > 1000049c: lis r9,16448 > 100004a0: efscmpeq cr7,r10,r9 > 100004a4: ble- cr7,0x100004b8 <bar+60> //jump to abort() call > 100004a8: lwz r10,12(r31) > 100004ac: lis r9,16512 > 100004b0: efscmpeq cr7,r10,r9 > 100004b4: bgt- cr7,0x100004bc <bar+64> //skip abort() call > 28 abort (); > 100004b8: bl 0x10000808 <abort> > > Signed-off-by: Talha Imran <talha_imran@mentor.com> Does this patch supersede the earlier patch you posted for efcmp instructions on e500v1? Or is it in addition to that patch? > --- > target-ppc/fpu_helper.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/target-ppc/fpu_helper.c b/target-ppc/fpu_helper.c > index b67ebca..6fd56a8 100644 > --- a/target-ppc/fpu_helper.c > +++ b/target-ppc/fpu_helper.c > @@ -1442,7 +1442,7 @@ static inline uint32_t efststeq(CPUPPCState *env, uint32_t op1, uint32_t op2) > #define HELPER_SINGLE_SPE_CMP(name) \ > uint32_t helper_e##name(CPUPPCState *env, uint32_t op1, uint32_t op2) \ > { \ > - return e##name(env, op1, op2) << 2; \ > + return e##name(env, op1, op2); \ > } > /* efststlt */ > HELPER_SINGLE_SPE_CMP(fststlt);
On 05/27/2016 06:37 AM, David Gibson wrote: > On Thu, May 19, 2016 at 05:11:35PM +0500, Talha Imran wrote: >> With specification at hand from the reference manual from Freescale >> http://cache.nxp.com/files/32bit/doc/ref_manual/SPEPEM.pdf , I have found a fix >> to efscmp* instructions handling in QEMU. >> ... >> Signed-off-by: Talha Imran <talha_imran@mentor.com> > > Does this patch supersede the earlier patch you posted for efcmp > instructions on e500v1? Or is it in addition to that patch? > [talha]: Yes, it supersedes the earlier patches. This is a better solution. >> --- >> target-ppc/fpu_helper.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/target-ppc/fpu_helper.c b/target-ppc/fpu_helper.c >> index b67ebca..6fd56a8 100644 >> --- a/target-ppc/fpu_helper.c >> +++ b/target-ppc/fpu_helper.c >> @@ -1442,7 +1442,7 @@ static inline uint32_t efststeq(CPUPPCState *env, uint32_t op1, uint32_t op2) >> #define HELPER_SINGLE_SPE_CMP(name) \ >> uint32_t helper_e##name(CPUPPCState *env, uint32_t op1, uint32_t op2) \ >> { \ >> - return e##name(env, op1, op2) << 2; \ >> + return e##name(env, op1, op2); \ >> } >> /* efststlt */ >> HELPER_SINGLE_SPE_CMP(fststlt); >
On Fri, May 27, 2016 at 07:43:46AM +0000, Imran, Talha wrote: > > On 05/27/2016 06:37 AM, David Gibson wrote: > > On Thu, May 19, 2016 at 05:11:35PM +0500, Talha Imran wrote: > >> With specification at hand from the reference manual from Freescale > >> http://cache.nxp.com/files/32bit/doc/ref_manual/SPEPEM.pdf , I have found a fix > >> to efscmp* instructions handling in QEMU. > >> > ... > >> Signed-off-by: Talha Imran <talha_imran@mentor.com> > > > > Does this patch supersede the earlier patch you posted for efcmp > > instructions on e500v1? Or is it in addition to that patch? > > > [talha]: Yes, it supersedes the earlier patches. This is a better > solution. Ok, I managed to read up enough on the SPE instructions to convince myself this was correct, so I've merged it to ppc-for-2.7. > > >> --- > >> target-ppc/fpu_helper.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/target-ppc/fpu_helper.c b/target-ppc/fpu_helper.c > >> index b67ebca..6fd56a8 100644 > >> --- a/target-ppc/fpu_helper.c > >> +++ b/target-ppc/fpu_helper.c > >> @@ -1442,7 +1442,7 @@ static inline uint32_t efststeq(CPUPPCState *env, uint32_t op1, uint32_t op2) > >> #define HELPER_SINGLE_SPE_CMP(name) \ > >> uint32_t helper_e##name(CPUPPCState *env, uint32_t op1, uint32_t op2) \ > >> { \ > >> - return e##name(env, op1, op2) << 2; \ > >> + return e##name(env, op1, op2); \ > >> } > >> /* efststlt */ > >> HELPER_SINGLE_SPE_CMP(fststlt); > > > >
diff --git a/target-ppc/fpu_helper.c b/target-ppc/fpu_helper.c index b67ebca..6fd56a8 100644 --- a/target-ppc/fpu_helper.c +++ b/target-ppc/fpu_helper.c @@ -1442,7 +1442,7 @@ static inline uint32_t efststeq(CPUPPCState *env, uint32_t op1, uint32_t op2) #define HELPER_SINGLE_SPE_CMP(name) \ uint32_t helper_e##name(CPUPPCState *env, uint32_t op1, uint32_t op2) \ { \ - return e##name(env, op1, op2) << 2; \ + return e##name(env, op1, op2); \ } /* efststlt */ HELPER_SINGLE_SPE_CMP(fststlt);
With specification at hand from the reference manual from Freescale http://cache.nxp.com/files/32bit/doc/ref_manual/SPEPEM.pdf , I have found a fix to efscmp* instructions handling in QEMU. efscmp* instructions in QEMU set crD (Condition Register nibble) values as (0b0100 << 2) = 0b10000 (consider the HELPER_SINGLE_SPE_CMP macro which left shifts the value returned by efscmp* handler by 2 bits). A value of 0b10000 is not correct according the to the reference manual. The reference manual expects efscmp* instructions to return a value of 0bx1xx. Please find attached a patch which disables left shifting in HELPER_SINGLE_SPE_CMP macro. This macro is used by efscmp* and efstst* instructions only. efstst* instruction handlers, in turn, call efscmp* handlers too. *Explanation:* Traditionally, each crD (condition register nibble) consist of 4 bits, which is set by comparisons as follows: crD = W X Y Z where W = Less than X = Greater than Y = Equal to However, efscmp* instructions being a special case return a binary result. (efscmpeq will set the crD = 0bx1xx iff when op1 == op2 and 0bx0xx otherwise; i.e. there is no notion of different crD values based on Less than, Greater than and Equal to). This effectively means that crD will store a "Greater than" comparison result iff efscmp* instruction comparison is TRUE. Compiler exploits this feature by checking for "Branch if Less than or Equal to" (ble instruction) OR "Branch if Greater than" (bgt instruction) for Branch if FALSE OR Branch if TRUE respectively after an efscmp* instruction. This can be seen in a assembly code snippet below: 27 if (__real__ x != 3.0f || __imag__ x != 4.0f) 10000498: lwz r10,8(r31) 1000049c: lis r9,16448 100004a0: efscmpeq cr7,r10,r9 100004a4: ble- cr7,0x100004b8 <bar+60> //jump to abort() call 100004a8: lwz r10,12(r31) 100004ac: lis r9,16512 100004b0: efscmpeq cr7,r10,r9 100004b4: bgt- cr7,0x100004bc <bar+64> //skip abort() call 28 abort (); 100004b8: bl 0x10000808 <abort> Signed-off-by: Talha Imran <talha_imran@mentor.com> --- target-ppc/fpu_helper.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)