Re: [PATCH] Add FUTEX_CMP_REQUEUE futex op

From: Martin Schwidefsky
Date: Mon Jun 07 2004 - 11:07:09 EST

> > My personal preference is:
> > 1) change s390* entry*.S so that all syscalls can use up to 6 arguments,
> >    otherwise we'll have the same problem every now and then
> >    (last syscall before this one was fadvise64_64 if I remember well)
> > 2) allow sys_futex to have 6 arguments (the 6th on the stack, get_user'ed
> >    from an s390 wrapper)
> > 3) special structure passed in 5th argument for FUTEX_CMP_REQUEUE
> > 4) your solution
> >    (you have a special wrapper around futex anyway, so why not to handle
> >    it there already and create completely new syscall).
>
> I have talked to Martin about it (he won't be online for one more week),
> and he proposed a variant of 2): sys_futex, and possibly further new
> syscalls that might get added, pass their sixth argument in %r7,
> which is easier to get by than the user stack. Unlike doing it in
> the standard system call path, this won't cause any overhead for
> the other syscalls, but we need some wrappers.

I prefer to store the additional argument in %r7 for ALL system calls
to avoid addtitional system call wrappers. That way new system calls
with 6 arguments can be added without problems. The store for the
additional 6th argument can be hidden in a agi slot so this is pretty
much the perfect solution.

blue skies,
Martin.

---

[PATCH] s390: add support for 6 system call arguments (FUTEX_CMP_REQUEUE).

This patch adds support for 6 system call arguments on s390. The
first exploiter of this will be the sys_futex system call for the
FUTEX_CMP_REQUEUE operation. The idea is simple: use register %r7
for the 6th argument. This can be extended to 7/8/9/... arguments
if there ever will be the need for it. To call the system call
function in the kernel the additional arguments needs to get stored
on the stack. 8 bytes are added to the head of struct pt_regs. %r7
is stored to the additional field for all system calls. The store
is hidden in a address-generation-interlock slot, it doesn't slow
down the system call path.

Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>

diffstat:
arch/s390/kernel/asm-offsets.c | 1 +
arch/s390/kernel/compat_wrapper.S | 2 ++
arch/s390/kernel/entry.S | 10 +++++++---
arch/s390/kernel/entry64.S | 10 +++++++---
arch/s390/kernel/ptrace.c | 10 +++++-----
include/asm-s390/ptrace.h | 1 +
6 files changed, 23 insertions(+), 11 deletions(-)

diff -urN linux-2.6/arch/s390/kernel/asm-offsets.c linux-2.6-s390/arch/s390/kernel/asm-offsets.c
--- linux-2.6/arch/s390/kernel/asm-offsets.c Mon May 10 04:32:26 2004
+++ linux-2.6-s390/arch/s390/kernel/asm-offsets.c Mon Jun 7 16:10:03 2004
@@ -32,6 +32,7 @@
DEFINE(__TI_cpu, offsetof(struct thread_info, cpu),);
DEFINE(__TI_precount, offsetof(struct thread_info, preempt_count),);
BLANK();
+ DEFINE(__PT_ARGS, offsetof(struct pt_regs, args),);
DEFINE(__PT_PSW, offsetof(struct pt_regs, psw),);
DEFINE(__PT_GPRS, offsetof(struct pt_regs, gprs),);
DEFINE(__PT_ORIG_GPR2, offsetof(struct pt_regs, orig_gpr2),);
diff -urN linux-2.6/arch/s390/kernel/compat_wrapper.S linux-2.6-s390/arch/s390/kernel/compat_wrapper.S
--- linux-2.6/arch/s390/kernel/compat_wrapper.S Mon Jun 7 16:07:24 2004
+++ linux-2.6-s390/arch/s390/kernel/compat_wrapper.S Mon Jun 7 16:07:53 2004
@@ -1097,6 +1097,8 @@
lgfr %r4,%r4 # int
llgtr %r5,%r5 # struct compat_timespec *
llgtr %r6,%r6 # u32 *
+ lgf %r0,164(%r15) # int
+ stg %r0,160(%r15)
jg compat_sys_futex # branch to system call

.globl sys32_setxattr_wrapper
diff -urN linux-2.6/arch/s390/kernel/entry.S linux-2.6-s390/arch/s390/kernel/entry.S
--- linux-2.6/arch/s390/kernel/entry.S Mon Jun 7 16:07:24 2004
+++ linux-2.6-s390/arch/s390/kernel/entry.S Mon Jun 7 16:11:55 2004
@@ -24,7 +24,8 @@
* Stack layout for the system_call stack entry.
* The first few entries are identical to the user_regs_struct.
*/
-SP_PTREGS = STACK_FRAME_OVERHEAD
+SP_PTREGS = STACK_FRAME_OVERHEAD
+SP_ARGS = STACK_FRAME_OVERHEAD + __PT_ARGS
SP_PSW = STACK_FRAME_OVERHEAD + __PT_PSW
SP_R0 = STACK_FRAME_OVERHEAD + __PT_GPRS
SP_R1 = STACK_FRAME_OVERHEAD + __PT_GPRS + 4
@@ -230,12 +231,14 @@
sysc_enter:
GET_THREAD_INFO # load pointer to task_struct to R9
sla %r7,2 # *4 and test for svc 0
- bnz BASED(sysc_do_restart) # svc number > 0
+ bnz BASED(sysc_nr_ok) # svc number > 0
# svc 0: system call number in %r1
cl %r1,BASED(.Lnr_syscalls)
- bnl BASED(sysc_do_restart)
+ bnl BASED(sysc_nr_ok)
lr %r7,%r1 # copy svc number to %r7
sla %r7,2 # *4
+sysc_nr_ok:
+ mvc SP_ARGS(4,%r15),SP_R7(%r15)
sysc_do_restart:
tm __TI_flags+3(%r9),(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT)
l %r8,sys_call_table-system_call(%r7,%r13) # get system call addr.
@@ -510,6 +513,7 @@
lr %r7,%r1 # copy svc number to %r7
sla %r7,2 # *4
pgm_svcstd:
+ mvc SP_ARGS(4,%r15),SP_R7(%r15)
tm __TI_flags+3(%r9),(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT)
l %r8,sys_call_table-system_call(%r7,%r13) # get system call addr.
bnz BASED(pgm_tracesys)
diff -urN linux-2.6/arch/s390/kernel/entry64.S linux-2.6-s390/arch/s390/kernel/entry64.S
--- linux-2.6/arch/s390/kernel/entry64.S Mon Jun 7 16:07:24 2004
+++ linux-2.6-s390/arch/s390/kernel/entry64.S Mon Jun 7 16:13:17 2004
@@ -24,7 +24,8 @@
* Stack layout for the system_call stack entry.
* The first few entries are identical to the user_regs_struct.
*/
-SP_PTREGS = STACK_FRAME_OVERHEAD
+SP_PTREGS = STACK_FRAME_OVERHEAD
+SP_ARGS = STACK_FRAME_OVERHEAD + __PT_ARGS
SP_PSW = STACK_FRAME_OVERHEAD + __PT_PSW
SP_R0 = STACK_FRAME_OVERHEAD + __PT_GPRS
SP_R1 = STACK_FRAME_OVERHEAD + __PT_GPRS + 8
@@ -214,13 +215,15 @@
sysc_enter:
GET_THREAD_INFO # load pointer to task_struct to R9
slag %r7,%r7,2 # *4 and test for svc 0
- jnz sysc_do_restart
+ jnz sysc_nr_ok
# svc 0: system call number in %r1
lghi %r0,NR_syscalls
clr %r1,%r0
- jnl sysc_do_restart
+ jnl sysc_nr_ok
lgfr %r7,%r1 # clear high word in r1
slag %r7,%r7,2 # svc 0: system call number in %r1
+sysc_nr_ok:
+ mvc SP_ARGS(8,%r15),SP_R7(%r15)
sysc_do_restart:
larl %r10,sys_call_table
#ifdef CONFIG_S390_SUPPORT
@@ -542,6 +545,7 @@
clr %r1,%r0
slag %r7,%r1,2
pgm_svcstd:
+ mvc SP_ARGS(8,%r15),SP_R7(%r15)
larl %r10,sys_call_table
#ifdef CONFIG_S390_SUPPORT
tm SP_PSW+3(%r15),0x01 # are we running in 31 bit mode ?
diff -urN linux-2.6/arch/s390/kernel/ptrace.c linux-2.6-s390/arch/s390/kernel/ptrace.c
--- linux-2.6/arch/s390/kernel/ptrace.c Mon May 10 04:33:19 2004
+++ linux-2.6-s390/arch/s390/kernel/ptrace.c Mon Jun 7 16:07:53 2004
@@ -141,7 +141,7 @@
/*
* psw and gprs are stored on the stack
*/
- tmp = *(addr_t *)((addr_t) __KSTK_PTREGS(child) + addr);
+ tmp = *(addr_t *)((addr_t) &__KSTK_PTREGS(child)->psw + addr);
if (addr == (addr_t) &dummy->regs.psw.mask)
/* Remove per bit from user psw. */
tmp &= ~PSW_MASK_PER;
@@ -215,7 +215,7 @@
high order bit but older gdb's rely on it */
data |= PSW_ADDR_AMODE;
#endif
- *(addr_t *)((addr_t) __KSTK_PTREGS(child) + addr) = data;
+ *(addr_t *)((addr_t) &__KSTK_PTREGS(child)->psw + addr) = data;

} else if (addr < (addr_t) (&dummy->regs.orig_gpr2)) {
/*
@@ -360,7 +360,7 @@
PSW32_ADDR_AMODE31;
} else {
/* gpr 0-15 */
- tmp = *(__u32 *)((addr_t) __KSTK_PTREGS(child) +
+ tmp = *(__u32 *)((addr_t) &__KSTK_PTREGS(child)->psw +
addr*2 + 4);
}
} else if (addr < (addr_t) (&dummy32->regs.orig_gpr2)) {
@@ -439,8 +439,8 @@
(__u64) tmp & PSW32_ADDR_INSN;
} else {
/* gpr 0-15 */
- *(__u32*)((addr_t) __KSTK_PTREGS(child) + addr*2 + 4) =
- tmp;
+ *(__u32*)((addr_t) &__KSTK_PTREGS(child)->psw
+ + addr*2 + 4) = tmp;
}
} else if (addr < (addr_t) (&dummy32->regs.orig_gpr2)) {
/*
diff -urN linux-2.6/include/asm-s390/ptrace.h linux-2.6-s390/include/asm-s390/ptrace.h
--- linux-2.6/include/asm-s390/ptrace.h Mon May 10 04:32:54 2004
+++ linux-2.6-s390/include/asm-s390/ptrace.h Mon Jun 7 16:07:53 2004
@@ -303,6 +303,7 @@
*/
struct pt_regs
{
+ unsigned long args[1];
psw_t psw;
unsigned long gprs[NUM_GPRS];
unsigned long orig_gpr2;
-
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