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Subjectrfc/rft: use r10 as current on x86-64
Hello Andi et al,

The patch below converts x86-64 to use r10 as the current pointer instead
of gs:pcurrent. This results in a ~34KB savings in the code segment of
the kernel. I've tested this with running a few regular applications,
plus a few 32 bit binaries. If this patch is interesting, it probably
makes sense to merge the thread info structure into the task_struct so
that the assembly bits for syscall entry can be cleaned up. Comments?

-ben
--
"Time is what keeps everything from happening all at once." -- John Wheeler
Don't Email: <dont@kvack.org>.


diff --git a/arch/x86_64/Makefile b/arch/x86_64/Makefile
index a9cd42e..e547830 100644
--- a/arch/x86_64/Makefile
+++ b/arch/x86_64/Makefile
@@ -31,6 +31,7 @@ cflags-$(CONFIG_MK8) += $(call cc-option
cflags-$(CONFIG_MPSC) += $(call cc-option,-march=nocona)
CFLAGS += $(cflags-y)

+CFLAGS += -ffixed-r10
CFLAGS += -mno-red-zone
CFLAGS += -mcmodel=kernel
CFLAGS += -pipe
diff --git a/arch/x86_64/ia32/ia32entry.S b/arch/x86_64/ia32/ia32entry.S
index e0eb0c7..cdb5918 100644
--- a/arch/x86_64/ia32/ia32entry.S
+++ b/arch/x86_64/ia32/ia32entry.S
@@ -99,6 +99,7 @@ sysenter_do_call:
cmpl $(IA32_NR_syscalls),%eax
jae ia32_badsys
IA32_ARG_FIXUP 1
+ movq %gs:pda_pcurrent,%r10
call *ia32_sys_call_table(,%rax,8)
movq %rax,RAX-ARGOFFSET(%rsp)
GET_THREAD_INFO(%r10)
@@ -127,6 +128,7 @@ sysenter_tracesys:
CLEAR_RREGS
movq $-ENOSYS,RAX(%rsp) /* really needed? */
movq %rsp,%rdi /* &pt_regs -> arg1 */
+ movq %gs:pda_pcurrent,%r10
call syscall_trace_enter
LOAD_ARGS ARGOFFSET /* reload args from stack in case ptrace changed it */
RESTORE_REST
@@ -198,6 +200,7 @@ cstar_do_call:
cmpl $IA32_NR_syscalls,%eax
jae ia32_badsys
IA32_ARG_FIXUP 1
+ movq %gs:pda_pcurrent,%r10
call *ia32_sys_call_table(,%rax,8)
movq %rax,RAX-ARGOFFSET(%rsp)
GET_THREAD_INFO(%r10)
@@ -220,6 +223,7 @@ cstar_tracesys:
CLEAR_RREGS
movq $-ENOSYS,RAX(%rsp) /* really needed? */
movq %rsp,%rdi /* &pt_regs -> arg1 */
+ movq %gs:pda_pcurrent,%r10
call syscall_trace_enter
LOAD_ARGS ARGOFFSET /* reload args from stack in case ptrace changed it */
RESTORE_REST
@@ -282,6 +286,7 @@ ia32_do_syscall:
cmpl $(IA32_NR_syscalls),%eax
jae ia32_badsys
IA32_ARG_FIXUP
+ movq %gs:pda_pcurrent,%r10
call *ia32_sys_call_table(,%rax,8) # xxx: rip relative
ia32_sysret:
movq %rax,RAX-ARGOFFSET(%rsp)
@@ -291,6 +296,7 @@ ia32_tracesys:
SAVE_REST
movq $-ENOSYS,RAX(%rsp) /* really needed? */
movq %rsp,%rdi /* &pt_regs -> arg1 */
+ movq %gs:pda_pcurrent,%r10
call syscall_trace_enter
LOAD_ARGS ARGOFFSET /* reload args from stack in case ptrace changed it */
RESTORE_REST
@@ -336,6 +342,7 @@ ENTRY(ia32_ptregs_common)
CFI_ADJUST_CFA_OFFSET -8
CFI_REGISTER rip, r11
SAVE_REST
+ movq %gs:pda_pcurrent,%r10
call *%rax
RESTORE_REST
jmp ia32_sysret /* misbalances the return cache */
diff --git a/arch/x86_64/kernel/entry.S b/arch/x86_64/kernel/entry.S
index 9ff4204..53a829c 100644
--- a/arch/x86_64/kernel/entry.S
+++ b/arch/x86_64/kernel/entry.S
@@ -201,6 +201,7 @@ ENTRY(system_call)
cmpq $__NR_syscall_max,%rax
ja badsys
movq %r10,%rcx
+ movq %gs:pda_pcurrent,%r10
call *sys_call_table(,%rax,8) # XXX: rip relative
movq %rax,RAX-ARGOFFSET(%rsp)
/*
@@ -235,6 +236,7 @@ sysret_careful:
sti
pushq %rdi
CFI_ADJUST_CFA_OFFSET 8
+ movq %gs:pda_pcurrent,%r10
call schedule
popq %rdi
CFI_ADJUST_CFA_OFFSET -8
@@ -266,12 +268,14 @@ tracesys:
movq $-ENOSYS,RAX(%rsp)
FIXUP_TOP_OF_STACK %rdi
movq %rsp,%rdi
+ movq %gs:pda_pcurrent,%r10
call syscall_trace_enter
LOAD_ARGS ARGOFFSET /* reload args from stack in case ptrace changed it */
RESTORE_REST
cmpq $__NR_syscall_max,%rax
ja 1f
movq %r10,%rcx /* fixup for C */
+ movq %gs:pda_pcurrent,%r10
call *sys_call_table(,%rax,8)
movq %rax,RAX-ARGOFFSET(%rsp)
1: SAVE_REST
@@ -324,6 +328,7 @@ int_careful:
sti
pushq %rdi
CFI_ADJUST_CFA_OFFSET 8
+ movq %gs:pda_pcurrent,%r10
call schedule
popq %rdi
CFI_ADJUST_CFA_OFFSET -8
@@ -409,6 +414,7 @@ ENTRY(stub_execve)
movq %r11, %r15
CFI_REGISTER rip, r15
FIXUP_TOP_OF_STACK %r11
+ movq %gs:pda_pcurrent,%r10
call sys_execve
GET_THREAD_INFO(%rcx)
bt $TIF_IA32,threadinfo_flags(%rcx)
@@ -441,6 +447,7 @@ ENTRY(stub_rt_sigreturn)
SAVE_REST
movq %rsp,%rdi
FIXUP_TOP_OF_STACK %r11
+ movq %gs:pda_pcurrent,%r10
call sys_rt_sigreturn
movq %rax,RAX(%rsp) # fixme, this could be done at the higher layer
RESTORE_REST
@@ -498,6 +505,7 @@ ENTRY(stub_rt_sigreturn)
cmoveq %rax,%rsp /*todo This needs CFI annotation! */
pushq %rdi # save old stack
CFI_ADJUST_CFA_OFFSET 8
+ movq %gs:pda_pcurrent,%r10
call \func
.endm

@@ -559,6 +567,7 @@ retint_careful:
sti
pushq %rdi
CFI_ADJUST_CFA_OFFSET 8
+ movq %gs:pda_pcurrent,%r10
call schedule
popq %rdi
CFI_ADJUST_CFA_OFFSET -8
@@ -574,6 +583,7 @@ retint_signal:
movq $-1,ORIG_RAX(%rsp)
xorl %esi,%esi # oldset
movq %rsp,%rdi # &pt_regs
+ movq %gs:pda_pcurrent,%r10
call do_notify_resume
RESTORE_REST
cli
@@ -592,6 +602,7 @@ retint_kernel:
jnc retint_restore_args
bt $9,EFLAGS-ARGOFFSET(%rsp) /* interrupts off? */
jnc retint_restore_args
+ movq %gs:pda_pcurrent,%r10
call preempt_schedule_irq
jmp exit_intr
#endif
@@ -682,6 +693,7 @@ ENTRY(spurious_interrupt)
testl %edx,%edx
js 1f
swapgs
+ movq %gs:pda_pcurrent,%r10
xorl %ebx,%ebx
1: movq %rsp,%rdi
movq ORIG_RAX(%rsp),%rsi
@@ -734,6 +746,7 @@ ENTRY(error_entry)
je error_kernelspace
error_swapgs:
swapgs
+ movq %gs:pda_pcurrent,%r10
error_sti:
movq %rdi,RDI(%rsp)
movq %rsp,%rdi
@@ -876,6 +889,7 @@ ENTRY(execve)
CFI_STARTPROC
FAKE_STACK_FRAME $0
SAVE_ALL
+ movq %gs:pda_pcurrent,%r10
call sys_execve
movq %rax, RAX(%rsp)
RESTORE_REST
@@ -953,6 +967,7 @@ paranoid_userspace:
jmp paranoid_userspace
paranoid_schedule:
sti
+ movq %gs:pda_pcurrent,%r10
call schedule
cli
jmp paranoid_userspace
diff --git a/arch/x86_64/kernel/process.c b/arch/x86_64/kernel/process.c
index 5afd63e..340bce2 100644
--- a/arch/x86_64/kernel/process.c
+++ b/arch/x86_64/kernel/process.c
@@ -435,8 +435,10 @@ int copy_thread(int nr, unsigned long cl

childregs->rax = 0;
childregs->rsp = rsp;
- if (rsp == ~0UL)
+ if (rsp == ~0UL) {
+ childregs->r10 = (long)p;
childregs->rsp = (unsigned long)childregs;
+ }

p->thread.rsp = (unsigned long) childregs;
p->thread.rsp0 = (unsigned long) (childregs+1);
@@ -568,6 +570,7 @@ __switch_to(struct task_struct *prev_p,
prev->userrsp = read_pda(oldrsp);
write_pda(oldrsp, next->userrsp);
write_pda(pcurrent, next_p);
+ current = next_p;
write_pda(kernelstack,
(unsigned long)next_p->thread_info + THREAD_SIZE - PDA_STACKOFFSET);

diff --git a/arch/x86_64/kernel/setup64.c b/arch/x86_64/kernel/setup64.c
index 06dc354..3af8688 100644
--- a/arch/x86_64/kernel/setup64.c
+++ b/arch/x86_64/kernel/setup64.c
@@ -132,16 +132,16 @@ void pda_init(int cpu)

if (cpu == 0) {
/* others are initialized in smpboot.c */
- pda->pcurrent = &init_task;
+ current = pda->pcurrent = &init_task;
pda->irqstackptr = boot_cpu_stack;
} else {
+ current = pda->pcurrent;
pda->irqstackptr = (char *)
__get_free_pages(GFP_ATOMIC, IRQSTACK_ORDER);
if (!pda->irqstackptr)
panic("cannot allocate irqstack for cpu %d", cpu);
}

-
pda->irqstackptr += IRQSTACKSIZE-64;
}

diff --git a/arch/x86_64/kernel/traps.c b/arch/x86_64/kernel/traps.c
index bf337f4..a6008ae 100644
--- a/arch/x86_64/kernel/traps.c
+++ b/arch/x86_64/kernel/traps.c
@@ -277,6 +277,7 @@ void show_registers(struct pt_regs *regs
const int cpu = safe_smp_processor_id();
struct task_struct *cur = cpu_pda[cpu].pcurrent;

+ current = cur;
rsp = regs->rsp;

printk("CPU %d ", cpu);
diff --git a/arch/x86_64/lib/copy_user.S b/arch/x86_64/lib/copy_user.S
index dfa358b..f24497d 100644
--- a/arch/x86_64/lib/copy_user.S
+++ b/arch/x86_64/lib/copy_user.S
@@ -95,6 +95,7 @@ copy_user_generic:
.previous
.Lcug:
pushq %rbx
+ pushq %r12
xorl %eax,%eax /*zero for the exception handler */

#ifdef FIX_ALIGNMENT
@@ -117,20 +118,20 @@ copy_user_generic:
.Ls1: movq (%rsi),%r11
.Ls2: movq 1*8(%rsi),%r8
.Ls3: movq 2*8(%rsi),%r9
-.Ls4: movq 3*8(%rsi),%r10
+.Ls4: movq 3*8(%rsi),%r12
.Ld1: movq %r11,(%rdi)
.Ld2: movq %r8,1*8(%rdi)
.Ld3: movq %r9,2*8(%rdi)
-.Ld4: movq %r10,3*8(%rdi)
+.Ld4: movq %r12,3*8(%rdi)

.Ls5: movq 4*8(%rsi),%r11
.Ls6: movq 5*8(%rsi),%r8
.Ls7: movq 6*8(%rsi),%r9
-.Ls8: movq 7*8(%rsi),%r10
+.Ls8: movq 7*8(%rsi),%r12
.Ld5: movq %r11,4*8(%rdi)
.Ld6: movq %r8,5*8(%rdi)
.Ld7: movq %r9,6*8(%rdi)
-.Ld8: movq %r10,7*8(%rdi)
+.Ld8: movq %r12,7*8(%rdi)

decq %rdx

@@ -169,6 +170,7 @@ copy_user_generic:
jnz .Lloop_1

.Lende:
+ popq %r12
popq %rbx
ret

diff --git a/arch/x86_64/lib/csum-copy.S b/arch/x86_64/lib/csum-copy.S
index 72fd55e..8e0ee5f 100644
--- a/arch/x86_64/lib/csum-copy.S
+++ b/arch/x86_64/lib/csum-copy.S
@@ -84,7 +84,7 @@ csum_partial_copy_generic:
/* main loop. clear in 64 byte blocks */
/* r9: zero, r8: temp2, rbx: temp1, rax: sum, rcx: saved length */
/* r11: temp3, rdx: temp4, r12 loopcnt */
- /* r10: temp5, rbp: temp6, r14 temp7, r13 temp8 */
+ /* r15: temp5, rbp: temp6, r14 temp7, r13 temp8 */
.p2align 4
.Lloop:
source
@@ -97,7 +97,7 @@ csum_partial_copy_generic:
movq 24(%rdi),%rdx

source
- movq 32(%rdi),%r10
+ movq 32(%rdi),%r15
source
movq 40(%rdi),%rbp
source
@@ -112,7 +112,7 @@ csum_partial_copy_generic:
adcq %r8,%rax
adcq %r11,%rax
adcq %rdx,%rax
- adcq %r10,%rax
+ adcq %r15,%rax
adcq %rbp,%rax
adcq %r14,%rax
adcq %r13,%rax
@@ -129,7 +129,7 @@ csum_partial_copy_generic:
movq %rdx,24(%rsi)

dest
- movq %r10,32(%rsi)
+ movq %r15,32(%rsi)
dest
movq %rbp,40(%rsi)
dest
@@ -149,7 +149,7 @@ csum_partial_copy_generic:
/* do last upto 56 bytes */
.Lhandle_tail:
/* ecx: count */
- movl %ecx,%r10d
+ movl %ecx,%r15d
andl $63,%ecx
shrl $3,%ecx
jz .Lfold
@@ -176,7 +176,7 @@ csum_partial_copy_generic:

/* do last upto 6 bytes */
.Lhandle_7:
- movl %r10d,%ecx
+ movl %r15d,%ecx
andl $7,%ecx
shrl $1,%ecx
jz .Lhandle_1
@@ -198,7 +198,7 @@ csum_partial_copy_generic:

/* handle last odd byte */
.Lhandle_1:
- testl $1,%r10d
+ testl $1,%r15d
jz .Lende
xorl %ebx,%ebx
source
diff --git a/include/asm-x86_64/current.h b/include/asm-x86_64/current.h
index bc8adec..6675f2d 100644
--- a/include/asm-x86_64/current.h
+++ b/include/asm-x86_64/current.h
@@ -6,13 +6,7 @@ struct task_struct;

#include <asm/pda.h>

-static inline struct task_struct *get_current(void)
-{
- struct task_struct *t = read_pda(pcurrent);
- return t;
-}
-
-#define current get_current()
+register struct task_struct *current __asm__("%r10");

#else

-
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