[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, 26 insertions, 22 deletions

diff --git a/include/asm-arm/unistd.h b/include/asm-arm/unistd.h
index d626e70fade..c9e087fe7e1 100644
--- a/include/asm-arm/unistd.h
+++ b/include/asm-arm/unistd.h
@@ -15,10 +15,12 @@
 
 #include <linux/linkage.h>
 
-#if defined(__thumb__)
+#define __NR_OABI_SYSCALL_BASE	0x900000
+
+#if defined(__thumb__) || defined(__ARM_EABI__)
 #define __NR_SYSCALL_BASE	0
 #else
-#define __NR_SYSCALL_BASE	0x900000
+#define __NR_SYSCALL_BASE	__NR_OABI_SYSCALL_BASE
 #endif
 
 /*
@@ -373,13 +375,13 @@
 #define __sys1(x) __sys2(x)
 
 #ifndef __syscall
-#if defined(__thumb__)
-#define __syscall(name)					\
-	"push	{r7}\n\t"				\
-	"mov	r7, #" __sys1(__NR_##name) "\n\t"	\
-	"swi	0\n\t"					\
-	"pop	{r7}"
+#if defined(__thumb__) || defined(__ARM_EABI__)
+#define __SYS_REG(name) register long __sysreg __asm__("r7") = __NR_##name;
+#define __SYS_REG_LIST(regs...) "r" (__sysreg) , ##regs
+#define __syscall(name) "swi\t0"
 #else
+#define __SYS_REG(name)
+#define __SYS_REG_LIST(regs...) regs
 #define __syscall(name) "swi\t" __sys1(__NR_##name) ""
 #endif
 #endif
@@ -395,33 +397,34 @@ do {									\
 
 #define _syscall0(type,name)						\
 type name(void) {							\
+  __SYS_REG(name)							\
   register long __res_r0 __asm__("r0");					\
   long __res;								\
   __asm__ __volatile__ (						\
   __syscall(name)							\
 	: "=r" (__res_r0)						\
-	:								\
-	: "lr");							\
+	: __SYS_REG_LIST() );						\
   __res = __res_r0;							\
   __syscall_return(type,__res);						\
 }
 
 #define _syscall1(type,name,type1,arg1) 				\
 type name(type1 arg1) { 						\
+  __SYS_REG(name)							\
   register long __r0 __asm__("r0") = (long)arg1;			\
   register long __res_r0 __asm__("r0");					\
   long __res;								\
   __asm__ __volatile__ (						\
   __syscall(name)							\
 	: "=r" (__res_r0)						\
-	: "r" (__r0)							\
-	: "lr");							\
+	: __SYS_REG_LIST( "0" (__r0) ) );				\
   __res = __res_r0;							\
   __syscall_return(type,__res);						\
 }
 
 #define _syscall2(type,name,type1,arg1,type2,arg2)			\
 type name(type1 arg1,type2 arg2) {					\
+  __SYS_REG(name)							\
   register long __r0 __asm__("r0") = (long)arg1;			\
   register long __r1 __asm__("r1") = (long)arg2;			\
   register long __res_r0 __asm__("r0");					\
@@ -429,8 +432,7 @@ type name(type1 arg1,type2 arg2) {					\
   __asm__ __volatile__ (						\
   __syscall(name)							\
 	: "=r" (__res_r0)						\
-	: "r" (__r0),"r" (__r1) 					\
-	: "lr");							\
+	: __SYS_REG_LIST( "0" (__r0), "r" (__r1) ) );			\
   __res = __res_r0;							\
   __syscall_return(type,__res);						\
 }
@@ -438,6 +440,7 @@ type name(type1 arg1,type2 arg2) {					\
 
 #define _syscall3(type,name,type1,arg1,type2,arg2,type3,arg3)		\
 type name(type1 arg1,type2 arg2,type3 arg3) {				\
+  __SYS_REG(name)							\
   register long __r0 __asm__("r0") = (long)arg1;			\
   register long __r1 __asm__("r1") = (long)arg2;			\
   register long __r2 __asm__("r2") = (long)arg3;			\
@@ -446,8 +449,7 @@ type name(type1 arg1,type2 arg2,type3 arg3) {				\
   __asm__ __volatile__ (						\
   __syscall(name)							\
 	: "=r" (__res_r0)						\
-	: "r" (__r0),"r" (__r1),"r" (__r2)				\
-	: "lr");							\
+	: __SYS_REG_LIST( "0" (__r0), "r" (__r1), "r" (__r2) ) );	\
   __res = __res_r0;							\
   __syscall_return(type,__res);						\
 }
@@ -455,6 +457,7 @@ type name(type1 arg1,type2 arg2,type3 arg3) {				\
 
 #define _syscall4(type,name,type1,arg1,type2,arg2,type3,arg3,type4,arg4)\
 type name(type1 arg1, type2 arg2, type3 arg3, type4 arg4) {		\
+  __SYS_REG(name)							\
   register long __r0 __asm__("r0") = (long)arg1;			\
   register long __r1 __asm__("r1") = (long)arg2;			\
   register long __r2 __asm__("r2") = (long)arg3;			\
@@ -464,8 +467,7 @@ type name(type1 arg1, type2 arg2, type3 arg3, type4 arg4) {		\
   __asm__ __volatile__ (						\
   __syscall(name)							\
 	: "=r" (__res_r0)						\
-	: "r" (__r0),"r" (__r1),"r" (__r2),"r" (__r3)			\
-	: "lr");							\
+	: __SYS_REG_LIST( "0" (__r0), "r" (__r1), "r" (__r2), "r" (__r3) ) ); \
   __res = __res_r0;							\
   __syscall_return(type,__res);						\
 }
@@ -473,6 +475,7 @@ type name(type1 arg1, type2 arg2, type3 arg3, type4 arg4) {		\
 
 #define _syscall5(type,name,type1,arg1,type2,arg2,type3,arg3,type4,arg4,type5,arg5)	\
 type name(type1 arg1, type2 arg2, type3 arg3, type4 arg4, type5 arg5) {	\
+  __SYS_REG(name)							\
   register long __r0 __asm__("r0") = (long)arg1;			\
   register long __r1 __asm__("r1") = (long)arg2;			\
   register long __r2 __asm__("r2") = (long)arg3;			\
@@ -483,14 +486,15 @@ type name(type1 arg1, type2 arg2, type3 arg3, type4 arg4, type5 arg5) {	\
   __asm__ __volatile__ (						\
   __syscall(name)							\
 	: "=r" (__res_r0)						\
-	: "r" (__r0),"r" (__r1),"r" (__r2),"r" (__r3),"r" (__r4)	\
-	: "lr");							\
+	: __SYS_REG_LIST( "0" (__r0), "r" (__r1), "r" (__r2),		\
+			  "r" (__r3), "r" (__r4) ) );			\
   __res = __res_r0;							\
   __syscall_return(type,__res);						\
 }
 
 #define _syscall6(type,name,type1,arg1,type2,arg2,type3,arg3,type4,arg4,type5,arg5,type6,arg6)	\
 type name(type1 arg1, type2 arg2, type3 arg3, type4 arg4, type5 arg5, type6 arg6) {	\
+  __SYS_REG(name)							\
   register long __r0 __asm__("r0") = (long)arg1;			\
   register long __r1 __asm__("r1") = (long)arg2;			\
   register long __r2 __asm__("r2") = (long)arg3;			\
@@ -502,8 +506,8 @@ type name(type1 arg1, type2 arg2, type3 arg3, type4 arg4, type5 arg5, type6 arg6
   __asm__ __volatile__ (						\
   __syscall(name)							\
 	: "=r" (__res_r0)						\
-	: "r" (__r0),"r" (__r1),"r" (__r2),"r" (__r3), "r" (__r4),"r" (__r5)		\
-	: "lr");							\
+	: __SYS_REG_LIST( "0" (__r0), "r" (__r1), "r" (__r2),		\
+			  "r" (__r3), "r" (__r4), "r" (__r5) ) );	\
   __res = __res_r0;							\
   __syscall_return(type,__res);						\
 }