diff options
Diffstat (limited to 'arch/arm/kernel/entry-armv.S')
| -rw-r--r-- | arch/arm/kernel/entry-armv.S | 213 |
1 files changed, 212 insertions, 1 deletions
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S index 2a5c3fe..080df90 100644 --- a/arch/arm/kernel/entry-armv.S +++ b/arch/arm/kernel/entry-armv.S @@ -269,6 +269,12 @@ __pabt_svc: add r5, sp, #S_PC ldmia r7, {r2 - r4} @ Get USR pc, cpsr +#if __LINUX_ARM_ARCH__ < 6 + @ make sure our user space atomic helper is aborted + cmp r2, #VIRT_OFFSET + bichs r3, r3, #PSR_Z_BIT +#endif + @ @ We are now ready to fill in the remaining blanks on the stack: @ @@ -499,8 +505,12 @@ ENTRY(__switch_to) mra r4, r5, acc0 stmia ip, {r4, r5} #endif +#ifdef CONFIG_HAS_TLS_REG + mcr p15, 0, r3, c13, c0, 3 @ set TLS register +#else mov r4, #0xffff0fff - str r3, [r4, #-3] @ Set TLS ptr + str r3, [r4, #-15] @ TLS val at 0xffff0ff0 +#endif mcr p15, 0, r6, c3, c0, 0 @ Set domain register #ifdef CONFIG_VFP @ Always disable VFP so we can lazily save/restore the old @@ -519,6 +529,207 @@ ENTRY(__switch_to) ldmib r2, {r4 - sl, fp, sp, pc} @ Load all regs saved previously __INIT + +/* + * User helpers. + * + * These are segment of kernel provided user code reachable from user space + * at a fixed address in kernel memory. This is used to provide user space + * with some operations which require kernel help because of unimplemented + * native feature and/or instructions in many ARM CPUs. The idea is for + * this code to be executed directly in user mode for best efficiency but + * which is too intimate with the kernel counter part to be left to user + * libraries. In fact this code might even differ from one CPU to another + * depending on the available instruction set and restrictions like on + * SMP systems. In other words, the kernel reserves the right to change + * this code as needed without warning. Only the entry points and their + * results are guaranteed to be stable. + * + * Each segment is 32-byte aligned and will be moved to the top of the high + * vector page. New segments (if ever needed) must be added in front of + * existing ones. This mechanism should be used only for things that are + * really small and justified, and not be abused freely. + * + * User space is expected to implement those things inline when optimizing + * for a processor that has the necessary native support, but only if such + * resulting binaries are already to be incompatible with earlier ARM + * processors due to the use of unsupported instructions other than what + * is provided here. In other words don't make binaries unable to run on + * earlier processors just for the sake of not using these kernel helpers + * if your compiled code is not going to use the new instructions for other + * purpose. + */ + + .align 5 + .globl __kuser_helper_start +__kuser_helper_start: + +/* + * Reference prototype: + * + * int __kernel_cmpxchg(int oldval, int newval, int *ptr) + * + * Input: + * + * r0 = oldval + * r1 = newval + * r2 = ptr + * lr = return address + * + * Output: + * + * r0 = returned value (zero or non-zero) + * C flag = set if r0 == 0, clear if r0 != 0 + * + * Clobbered: + * + * r3, ip, flags + * + * Definition and user space usage example: + * + * typedef int (__kernel_cmpxchg_t)(int oldval, int newval, int *ptr); + * #define __kernel_cmpxchg (*(__kernel_cmpxchg_t *)0xffff0fc0) + * + * Atomically store newval in *ptr if *ptr is equal to oldval for user space. + * Return zero if *ptr was changed or non-zero if no exchange happened. + * The C flag is also set if *ptr was changed to allow for assembly + * optimization in the calling code. + * + * For example, a user space atomic_add implementation could look like this: + * + * #define atomic_add(ptr, val) \ + * ({ register unsigned int *__ptr asm("r2") = (ptr); \ + * register unsigned int __result asm("r1"); \ + * asm volatile ( \ + * "1: @ atomic_add\n\t" \ + * "ldr r0, [r2]\n\t" \ + * "mov r3, #0xffff0fff\n\t" \ + * "add lr, pc, #4\n\t" \ + * "add r1, r0, %2\n\t" \ + * "add pc, r3, #(0xffff0fc0 - 0xffff0fff)\n\t" \ + * "bcc 1b" \ + * : "=&r" (__result) \ + * : "r" (__ptr), "rIL" (val) \ + * : "r0","r3","ip","lr","cc","memory" ); \ + * __result; }) + */ + +__kuser_cmpxchg: @ 0xffff0fc0 + +#if __LINUX_ARM_ARCH__ < 6 + +#ifdef CONFIG_SMP /* sanity check */ +#error "CONFIG_SMP on a machine supporting pre-ARMv6 processors?" +#endif + + /* + * Theory of operation: + * + * We set the Z flag before loading oldval. If ever an exception + * occurs we can not be sure the loaded value will still be the same + * when the exception returns, therefore the user exception handler + * will clear the Z flag whenever the interrupted user code was + * actually from the kernel address space (see the usr_entry macro). + * + * The post-increment on the str is used to prevent a race with an + * exception happening just after the str instruction which would + * clear the Z flag although the exchange was done. + */ + teq ip, ip @ set Z flag + ldr ip, [r2] @ load current val + add r3, r2, #1 @ prepare store ptr + teqeq ip, r0 @ compare with oldval if still allowed + streq r1, [r3, #-1]! @ store newval if still allowed + subs r0, r2, r3 @ if r2 == r3 the str occured + mov pc, lr + +#else + + ldrex r3, [r2] + subs r3, r3, r0 + strexeq r3, r1, [r2] + rsbs r0, r3, #0 + mov pc, lr + +#endif + + .align 5 + +/* + * Reference prototype: + * + * int __kernel_get_tls(void) + * + * Input: + * + * lr = return address + * + * Output: + * + * r0 = TLS value + * + * Clobbered: + * + * the Z flag might be lost + * + * Definition and user space usage example: + * + * typedef int (__kernel_get_tls_t)(void); + * #define __kernel_get_tls (*(__kernel_get_tls_t *)0xffff0fe0) + * + * Get the TLS value as previously set via the __ARM_NR_set_tls syscall. + * + * This could be used as follows: + * + * #define __kernel_get_tls() \ + * ({ register unsigned int __val asm("r0"); \ + * asm( "mov r0, #0xffff0fff; mov lr, pc; sub pc, r0, #31" \ + * : "=r" (__val) : : "lr","cc" ); \ + * __val; }) + */ + +__kuser_get_tls: @ 0xffff0fe0 + +#ifndef CONFIG_HAS_TLS_REG + +#ifdef CONFIG_SMP /* sanity check */ +#error "CONFIG_SMP without CONFIG_HAS_TLS_REG is wrong" +#endif + + ldr r0, [pc, #(16 - 8)] @ TLS stored at 0xffff0ff0 + mov pc, lr + +#else + + mrc p15, 0, r0, c13, c0, 3 @ read TLS register + mov pc, lr + +#endif + + .rep 5 + .word 0 @ pad up to __kuser_helper_version + .endr + +/* + * Reference declaration: + * + * extern unsigned int __kernel_helper_version; + * + * Definition and user space usage example: + * + * #define __kernel_helper_version (*(unsigned int *)0xffff0ffc) + * + * User space may read this to determine the curent number of helpers + * available. + */ + +__kuser_helper_version: @ 0xffff0ffc + .word ((__kuser_helper_end - __kuser_helper_start) >> 5) + + .globl __kuser_helper_end +__kuser_helper_end: + + /* * Vector stubs. * |