Message ID | 1437461926-8908-5-git-send-email-khandual@linux.vnet.ibm.com (mailing list archive) |
---|---|
State | Changes Requested |
Headers | show |
On Tue, 2015-07-21 at 12:28 +0530, Anshuman Khandual wrote: > From: "khandual@linux.vnet.ibm.com" <khandual@linux.vnet.ibm.com> > > This patch adds some documentation to 'patch_slb_encoding' function > explaining about how it clears the existing immediate value in the > given instruction and inserts a new one there. > > diff --git a/arch/powerpc/mm/slb.c b/arch/powerpc/mm/slb.c > index dcba4c2..8083a9e 100644 > --- a/arch/powerpc/mm/slb.c > +++ b/arch/powerpc/mm/slb.c > @@ -278,7 +278,13 @@ void switch_slb(struct task_struct *tsk, struct mm_struct *mm) > static inline void patch_slb_encoding(unsigned int *insn_addr, > unsigned int immed) > { > - int insn = (*insn_addr & 0xffff0000) | immed; > + /* > + * Currently this patches only "li" and "cmpldi" > + * instructions with an immediate value. Here it > + * just clears the existing immediate value from > + * the instruction and inserts a new one there. > + */ > + unsigned int insn = (*insn_addr & 0xffff0000) | immed; > patch_instruction(insn_addr, insn); > } How about: /* * This function patches either an li or a cmpldi instruction with * a new immediate value. This relies on the fact that both li * (which is actually ori) and cmpldi both take a 16-bit immediate * value, and it is situated in the same location in the instruction, * ie. bits 0-15. * To patch the value we read the existing instruction, clear the * immediate value, and or in our new value, then write the instruction * back. */ cheers
On Wed, Jul 22, 2015 at 03:51:03PM +1000, Michael Ellerman wrote: > On Tue, 2015-07-21 at 12:28 +0530, Anshuman Khandual wrote: > > From: "khandual@linux.vnet.ibm.com" <khandual@linux.vnet.ibm.com> > > > > This patch adds some documentation to 'patch_slb_encoding' function > > explaining about how it clears the existing immediate value in the > > given instruction and inserts a new one there. > > > > diff --git a/arch/powerpc/mm/slb.c b/arch/powerpc/mm/slb.c > > index dcba4c2..8083a9e 100644 > > --- a/arch/powerpc/mm/slb.c > > +++ b/arch/powerpc/mm/slb.c > > @@ -278,7 +278,13 @@ void switch_slb(struct task_struct *tsk, struct mm_struct *mm) > > static inline void patch_slb_encoding(unsigned int *insn_addr, > > unsigned int immed) > > { > > - int insn = (*insn_addr & 0xffff0000) | immed; > > + /* > > + * Currently this patches only "li" and "cmpldi" > > + * instructions with an immediate value. Here it > > + * just clears the existing immediate value from > > + * the instruction and inserts a new one there. > > + */ > > + unsigned int insn = (*insn_addr & 0xffff0000) | immed; > > patch_instruction(insn_addr, insn); > > } > > > How about: > > /* > * This function patches either an li or a cmpldi instruction with > * a new immediate value. This relies on the fact that both li > * (which is actually ori) and cmpldi both take a 16-bit immediate Hmm, li is actually encoded as addi with r0 as source register... > * value, and it is situated in the same location in the instruction, > * ie. bits 0-15. In PPC documentation, it's rather bits 16-31 (big endian bit order). Or say lower half which is endian agnostic. Cheers, Gabriel
On Wed, 2015-07-22 at 07:57 +0200, Gabriel Paubert wrote: > On Wed, Jul 22, 2015 at 03:51:03PM +1000, Michael Ellerman wrote: > > On Tue, 2015-07-21 at 12:28 +0530, Anshuman Khandual wrote: > > > From: "khandual@linux.vnet.ibm.com" <khandual@linux.vnet.ibm.com> > > > > > > This patch adds some documentation to 'patch_slb_encoding' function > > > explaining about how it clears the existing immediate value in the > > > given instruction and inserts a new one there. > > > > > > diff --git a/arch/powerpc/mm/slb.c b/arch/powerpc/mm/slb.c > > > index dcba4c2..8083a9e 100644 > > > --- a/arch/powerpc/mm/slb.c > > > +++ b/arch/powerpc/mm/slb.c > > > @@ -278,7 +278,13 @@ void switch_slb(struct task_struct *tsk, struct mm_struct *mm) > > > static inline void patch_slb_encoding(unsigned int *insn_addr, > > > unsigned int immed) > > > { > > > - int insn = (*insn_addr & 0xffff0000) | immed; > > > + /* > > > + * Currently this patches only "li" and "cmpldi" > > > + * instructions with an immediate value. Here it > > > + * just clears the existing immediate value from > > > + * the instruction and inserts a new one there. > > > + */ > > > + unsigned int insn = (*insn_addr & 0xffff0000) | immed; > > > patch_instruction(insn_addr, insn); > > > } > > > > > > How about: > > > > /* > > * This function patches either an li or a cmpldi instruction with > > * a new immediate value. This relies on the fact that both li > > * (which is actually ori) and cmpldi both take a 16-bit immediate > > Hmm, li is actually encoded as addi with r0 as source register... Correct. > > * value, and it is situated in the same location in the instruction, > > * ie. bits 0-15. > > In PPC documentation, it's rather bits 16-31 (big endian bit order). > Or say lower half which is endian agnostic. Yeah, but who reads the PPC documentation ;) In the kernel we almost always use the sane bit numbering, so I'd use that, but maybe "low 16-bits" will avoid confusion. cheers
On Wed, Jul 22, 2015 at 03:51:03PM +1000, Michael Ellerman wrote: > How about: > > /* > * This function patches either an li or a cmpldi instruction with > * a new immediate value. This relies on the fact that both li > * (which is actually ori) and cmpldi both take a 16-bit immediate > * value, and it is situated in the same location in the instruction, > * ie. bits 0-15. > * To patch the value we read the existing instruction, clear the > * immediate value, and or in our new value, then write the instruction > * back. > */ As Gabriel says, li is addi. It takes a 16-bit sign-extended immediate, while cmpldi takes a 16-bit zero-extended immediate. This function doesn't deal with that difference, it probably should (I didn't check if the callers take care; there should be an assertion somewhere). Segher
diff --git a/arch/powerpc/mm/slb.c b/arch/powerpc/mm/slb.c index dcba4c2..8083a9e 100644 --- a/arch/powerpc/mm/slb.c +++ b/arch/powerpc/mm/slb.c @@ -278,7 +278,13 @@ void switch_slb(struct task_struct *tsk, struct mm_struct *mm) static inline void patch_slb_encoding(unsigned int *insn_addr, unsigned int immed) { - int insn = (*insn_addr & 0xffff0000) | immed; + /* + * Currently this patches only "li" and "cmpldi" + * instructions with an immediate value. Here it + * just clears the existing immediate value from + * the instruction and inserts a new one there. + */ + unsigned int insn = (*insn_addr & 0xffff0000) | immed; patch_instruction(insn_addr, insn); }