diff options
Diffstat (limited to 'nuttx/arch/arm/src/armv7-m/up_svcall.c')
| -rw-r--r-- | nuttx/arch/arm/src/armv7-m/up_svcall.c | 24 |
1 files changed, 16 insertions, 8 deletions
diff --git a/nuttx/arch/arm/src/armv7-m/up_svcall.c b/nuttx/arch/arm/src/armv7-m/up_svcall.c index 48ab00eba..078f85606 100644 --- a/nuttx/arch/arm/src/armv7-m/up_svcall.c +++ b/nuttx/arch/arm/src/armv7-m/up_svcall.c @@ -92,6 +92,18 @@ * Description: * Call the stub function corresponding to the system call. * + * Here we need to preserve registers: + * + * R0 - Need not be preserved until after the stub is called. + * R1-R3 - Need to be preserved until the stub is called. The values of + * R0 and R1 returned by the stub must be preserved. + * R4-R11 must be preserved to support the expectations of the user-space + * callee + * R12 - Need not be preserved + * R13 - (stack pointer) + * R14 - Need not be preserved + * R15 - (PC) + * ****************************************************************************/ #ifdef CONFIG_NUTTX_KERNEL @@ -100,14 +112,10 @@ static void dispatch_syscall(void) { __asm__ __volatile__ ( - " push {r4, r5}\n" /* Save R4 and R5 */ - " mov r5, r14\n" /* Save LR in R5 */ - " ldr r4, =g_stublookup\n" /* Get the base of the stub lookup table */ - " ldr r4, [r4, r0, lsl #2]\n" /* Load the entry of the stub for this syscall */ - " blx r4\n" /* Call the stub */ - " mov r14, r5\n" /* Restore R14 */ - " pop {r4, r5}\n" /* Restore R4 and R5 */ - " mov r2, r0\n" /* Save the return value in R0 in R2 for now */ + " ldr ip, =g_stublookup\n" /* R12=The base of the stub lookup table */ + " ldr ip, [ip, r0, lsl #2]\n" /* R12=The address of the stub for this syscall */ + " blx ip\n" /* Call the stub (modifies R14)*/ + " mov r2, r0\n" /* R2=Saved return value in R0 */ " mov r0, #3\n" /* R0=SYS_syscall_return */ " svc 0" /* Return from the syscall */ ::: |