[ARM] 3105/4: ARM EABI: new syscall entry convention

Patch from Nicolas Pitre

For a while we wanted to change the way syscalls were called on ARM.
Instead of encoding the syscall number in the swi instruction which
requires reading back the instruction from memory to extract that number
and polluting the data cache, it was decided that simply storing the
syscall number into r7 would be more efficient. Since this represents
an ABI change then making that change at the same time as EABI support
is the right thing to do.

It is now expected that EABI user space binaries put the syscall number
into r7 and use "swi 0" to call the kernel. Syscall register argument
are also expected to have "EABI arrangement" i.e. 64-bit arguments
should be put in a pair of registers from an even register number.

Example with long ftruncate64(unsigned int fd, loff_t length):

	legacy ABI:
	- put fd into r0
	- put length into r1-r2
	- use "swi #(0x900000 + 194)" to call the kernel

	new ARM EABI:
	- put fd into r0
	- put length into r2-r3 (skipping over r1)
	- put 194 into r7
	- use "swi 0" to call the kernel

Note that it is important to use 0 for the swi argument as backward
compatibility with legacy ABI user space relies on this.
The syscall macros in asm-arm/unistd.h were also updated to support
both ABIs and implement the right call method automatically.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 21 insertions, 14 deletions

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index e2b42997ad33..34826bcceb7a 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -98,20 +98,14 @@ ENTRY(ret_from_fork)
            run on an ARM7 and we can save a couple of instructions.  
                                                                 --pb */
 #ifdef CONFIG_CPU_ARM710
-        .macro  arm710_bug_check, instr, temp
-        and     \temp, \instr, #0x0f000000      @ check for SWI
-        teq     \temp, #0x0f000000
-        bne     .Larm700bug
-        .endm
-
-.Larm700bug:
+#define A710(code...) code
+.Larm710bug:
         ldmia   sp, {r0 - lr}^                  @ Get calling r0 - lr
         mov     r0, r0
         add     sp, sp, #S_FRAME_SIZE
         subs    pc, lr, #4
 #else
-        .macro  arm710_bug_check, instr, temp
-        .endm
+#define A710(code...)
 #endif
 
         .align  5
@@ -129,14 +123,24 @@ ENTRY(vector_swi)
         /*
          * Get the system call number.
          */
-#ifdef CONFIG_ARM_THUMB
+#if defined(CONFIG_AEABI)
+
+        @ syscall number is in scno (r7) already.
+
+  A710( ldr     ip, [lr, #-4]                   @ get SWI instruction   )
+  A710( and     ip, ip, #0x0f000000             @ check for SWI         )
+  A710( teq     ip, #0x0f000000                                         )
+  A710( bne     .Larm710bug                                             )
+#elif defined(CONFIG_ARM_THUMB)
         tst     r8, #PSR_T_BIT                  @ this is SPSR from save_user_regs
         addne   scno, r7, #__NR_SYSCALL_BASE    @ put OS number in
         ldreq   scno, [lr, #-4]
 #else
         ldr     scno, [lr, #-4]                 @ get SWI instruction
+  A710( and     ip, scno, #0x0f000000           @ check for SWI         )
+  A710( teq     ip, #0x0f000000                                         )
+  A710( bne     .Larm710bug                                             )
 #endif
-        arm710_bug_check scno, ip
 
 #ifdef CONFIG_ALIGNMENT_TRAP
         ldr     ip, __cr_alignment
@@ -145,18 +149,19 @@ ENTRY(vector_swi)
 #endif
         enable_irq
 
-        stmdb   sp!, {r4, r5}                   @ push fifth and sixth args
-
         get_thread_info tsk
         ldr     ip, [tsk, #TI_FLAGS]            @ check for syscall tracing
+#ifndef CONFIG_AEABI
         bic     scno, scno, #0xff000000         @ mask off SWI op-code
         eor     scno, scno, #__NR_SYSCALL_BASE  @ check OS number
+#endif
         adr     tbl, sys_call_table             @ load syscall table pointer
+        stmdb   sp!, {r4, r5}                   @ push fifth and sixth args
         tst     ip, #_TIF_SYSCALL_TRACE         @ are we tracing syscalls?
         bne     __sys_trace
 
-        adr     lr, ret_fast_syscall            @ return address
         cmp     scno, #NR_syscalls              @ check upper syscall limit
+        adr     lr, ret_fast_syscall            @ return address
         ldrcc   pc, [tbl, scno, lsl #2]         @ call sys_* routine
 
         add     r1, sp, #S_OFF
@@ -207,6 +212,7 @@ ENTRY(sys_call_table)
 @ r8 = syscall table
                 .type   sys_syscall, #function
 sys_syscall:
+#ifndef CONFIG_AEABI
                 eor     scno, r0, #__NR_SYSCALL_BASE
                 cmp     scno, #__NR_syscall - __NR_SYSCALL_BASE
                 cmpne   scno, #NR_syscalls      @ check range
@@ -216,6 +222,7 @@ sys_syscall:
                 movlo   r2, r3
                 movlo   r3, r4
                 ldrlo   pc, [tbl, scno, lsl #2]
+#endif
                 b       sys_ni_syscall
 
 sys_fork_wrapper: