From: Kees Jongenburger Date: Mon, 10 Feb 2014 12:12:21 +0000 (+0100) Subject: arm-refactor:document ARM assembly code. X-Git-Tag: v3.3.0~646 X-Git-Url: http://zhaoyanbai.com/repos/%22http:/www.isc.org/icons/doc/syslog.3.html?a=commitdiff_plain;h=3df19a0671523ca8a027f62ee3c04fef97f9f4bd;p=minix.git arm-refactor:document ARM assembly code. Change-Id: I8540a09cdaf45431ad163954ce41d36f4b72cad5 --- diff --git a/kernel/arch/earm/head.S b/kernel/arch/earm/head.S index c4192efac..03f9f97e0 100644 --- a/kernel/arch/earm/head.S +++ b/kernel/arch/earm/head.S @@ -28,20 +28,20 @@ MINIX: b multiboot_init multiboot_init: - ldr sp, =load_stack_start /* make usable stack */ + ldr sp, =load_stack_start /* make usable stack */ mov fp, #0 bl _C_LABEL(pre_init) /* Kernel is mapped high now and ready to go, with - * the boot info pointer returned in r0. Set the - * highly mapped stack, initialize it, push the boot - * info pointer and jump to the highly mapped kernel. + * the boot info pointer returned by pre_init in r0. + * Set the highly mapped stack and initialize it. + * + * Afther that call kmain with r0 still pointing to boot info */ ldr sp, =k_initial_stktop mov r1, #0 - push {r1} /* Terminate stack */ - /* r0 holds kinfo_t ptr */ - ldr r2, =_C_LABEL(kmain) + push {r1} /* Terminate stack */ + ldr r2, =_C_LABEL(kmain) /* r0 holds kinfo_t ptr */ bx r2 /* not reached */ diff --git a/kernel/arch/earm/mpx.S b/kernel/arch/earm/mpx.S index 4eafaecae..f1bfe9413 100644 --- a/kernel/arch/earm/mpx.S +++ b/kernel/arch/earm/mpx.S @@ -34,42 +34,52 @@ IMPORT(svc_stack) /* - * Adjust lr, switch to SVC mode, and push pc/psr when exception triggered - * The 'lr_offset' argument holds the adjustment. It differs based on - * which mode the CPU is in. + * Adjust lr, push pc/psr when exception triggered and switch to SVC mode + * The 'lr_offset' argument holds the adjustment. + * + * When an instruction causes the ARM core to enter the exception handler + * the value of pc is stored in the link register (lr). By default on ARM + * the program counter is 3 instruction a head of the current instruction + * being executed (because of the 3 stage pipeline). Depending on where in + * the pipeline the exception happens lr will need to de adjusted to find + * the proper return address. */ .macro switch_to_svc lr_offset - sub lr, lr, #\lr_offset - srsdb sp!, #MODE_SVC - cps #MODE_SVC + sub lr, lr, #\lr_offset /* do the adjustment */ + srsdb sp!, #MODE_SVC /* store the saved the return */ + /* address and program status */ + /* register onto the kernel stack */ + /* Also modify the stack pointer. */ + cps #MODE_SVC /* do the switch to SVC. */ .endm /* - * Test if the exception/interrupt occured in the kernel. + * Test if the exception/interrupt occurred in the kernel. * Jump to 'label' argument if it occurred in the kernel. * - * NOTE: switch_to_svc must be called first - */ + * NOTE: switch_to_svc must be called first */ .macro test_int_in_kernel, label push {r3} - ldr r3, [sp, #8] /* spsr */ - orr r3, r3, #(PSR_F | PSR_I) /* mask interrupts on return */ - str r3, [sp, #8] /* spsr */ - and r3, r3, #PSR_MODE_MASK - cmp r3, #MODE_USR + ldr r3, [sp, #8] /* get spsr. */ + orr r3, r3, #(PSR_F | PSR_I) /* mask interrupts on return. */ + str r3, [sp, #8] /* store spsr. */ + and r3, r3, #PSR_MODE_MASK /* mask the ARM mode. */ + cmp r3, #MODE_USR /* compare it to user mode. */ pop {r3} - bne \label /* In-kernel handling */ + bne \label /* In-kernel handling. */ .endm /* Save the register context to the proc structure */ .macro save_process_ctx - add sp, sp, #8 /* srsdb pushed cpsr and pc on the stack */ - ldr lr, [sp] /* lr = proc_ptr */ - stm lr, {r0-r14}^ /* proc_ptr->p_reg.r0-r14 = r0-r14 */ - ldr r12, [sp, #-8] /* r12 = pc stored on the stack */ - str r12, [lr, #PCREG] /* proc_ptr->p_reg.pc = r12 */ - ldr r12, [sp, #-4] /* r12 = cpsr stored on the stack */ - str r12, [lr, #PSREG] /* proc_ptr->p_reg.psr = r12 */ + add sp, sp, #8 /* We expect srsdb pushed cpsr and lr on */ + /* the stack. */ + ldr lr, [sp] /* lr = proc_ptr. */ + stm lr, {r0-r14}^ /* store the user mode registers */ + /* proc_ptr->p_reg.r0-r14 = r0-r14. */ + ldr r12, [sp, #-8] /* r12 = pc stored on the stack. */ + str r12, [lr, #PCREG] /* proc_ptr->p_reg.pc = r12. */ + ldr r12, [sp, #-4] /* r12 = cpsr stored on the stack. */ + str r12, [lr, #PSREG] /* proc_ptr->p_reg.psr = r12. */ .endm .macro exception_handler exc_name, exc_num, lr_offset @@ -80,14 +90,13 @@ ENTRY(\exc_name\()_entry) \exc_name\()entry_from_user: save_process_ctx - /* save the pointer to the current process */ - ldr fp, [sp] - /* save the exception pc (saved lr_user) */ - add r4, fp, #PCREG + ldr fp, [sp] /* save the pointer to the current process. */ + add r4, fp, #PCREG /* save the exception pc (saved lr_user) */ + /* r4-r9 are callee save. */ /* stop user process cycles */ - mov r0, fp /* first param: caller proc ptr */ - mov fp, #0 /* for stack trace */ + mov r0, fp /* first param: caller proc ptr. */ + mov fp, #0 /* for stack trace. */ bl _C_LABEL(context_stop) /* @@ -95,17 +104,16 @@ ENTRY(\exc_name\()_entry) * vector number pushed by the vector handler just before calling * exception_entry and call the exception handler. */ - mov r0, #0 /* it's not a nested exception */ - mov r1, r4 /* saved lr */ + mov r0, #0 /* it is not a nested exception. */ + mov r1, r4 /* saved lr. */ mov r2, #\exc_num /* vector number */ bl _C_LABEL(exception_handler) - b _C_LABEL(switch_to_user) \exc_name\()_entry_nested: push {r0-r12, lr} - mov r0, #1 /* it's a nested exception */ - add r1, sp, #56 /* saved lr */ + mov r0, #1 /* it is a nested exception. */ + add r1, sp, #56 /* saved lr */ mov r2, #\exc_num /* vector number */ bl _C_LABEL(exception_handler) pop {r0-r12, lr} @@ -129,22 +137,20 @@ irq_entry_from_user: /* save the pointer to the current process */ ldr fp, [sp] - push {fp} /* save caller proc ptr */ - sub sp, sp, #4 /* maintain stack alignment */ + push {fp} /* save caller proc ptr. */ + sub sp, sp, #4 /* maintain stack alignment. */ /* stop user process cycles */ - mov r0, fp /* first param: caller proc ptr */ - mov fp, #0 /* for stack trace */ + mov r0, fp /* first param: caller proc ptr. */ + mov fp, #0 /* for stack trace. */ bl _C_LABEL(context_stop) /* call handler */ bl _C_LABEL(bsp_irq_handle) /* bsp_irq_handle(void) */ add sp, sp, #4 - pop {fp} /* caller proc ptr */ - - /* data synchronization barrier */ - dsb + pop {fp} /* caller proc ptr. */ + dsb /* data synchronization barrier. */ b _C_LABEL(switch_to_user) @@ -153,11 +159,9 @@ irq_entry_from_kernel: bl _C_LABEL(context_stop_idle) /* call handler */ - bl _C_LABEL(bsp_irq_handle) /* bsp_irq_handle(void) */ - - /* data synchronization barrier */ - dsb + bl _C_LABEL(bsp_irq_handle) /* bsp_irq_handle(void). */ + /* data synchronization barrier */ dsb pop {r0-r12, lr} rfeia sp! @@ -166,6 +170,7 @@ irq_entry_from_kernel: * supervisor call (SVC) kernel entry point */ ENTRY(svc_entry) + /* Store the LR and the SPSR of the current mode onto the SVC stack */ srsdb sp!, #MODE_SVC save_process_ctx @@ -187,20 +192,20 @@ ENTRY(svc_entry) */ ENTRY(kernel_call_entry) /* - * pass the syscall arguments from userspace to the handler. + * pass the syscall arguments from userspace to the handler. * save_process_ctx() does not clobber these registers, they are still - * set as the userspace has set them + * set as the userspace has set them. */ - push {fp} /* save caller proc ptr */ - push {r0} /* save msg ptr so it's not clobbered */ + push {fp} /* save caller proc ptr. */ + push {r0} /* save msg ptr so it's not clobbered. */ /* stop user process cycles */ - mov r0, fp /* first param: caller proc ptr */ - mov fp, #0 /* for stack trace */ + mov r0, fp /* first param: caller proc ptr */ + mov fp, #0 /* for stack trace */ bl _C_LABEL(context_stop) - pop {r0} /* first param: msg ptr */ - pop {r1} /* second param: caller proc ptr */ + pop {r0} /* first param: msg ptr. */ + pop {r1} /* second param: caller proc ptr. */ bl _C_LABEL(kernel_call) b _C_LABEL(switch_to_user) @@ -214,19 +219,19 @@ ENTRY(ipc_entry) * save_process_ctx() does not clobber these registers, they are still * set as the userspace have set them */ - push {fp} /* save caller proc ptr */ - push {r0-r2} /* save regs so they're not clobbered */ + push {fp} /* save caller proc ptr. */ + push {r0-r2} /* save regs so they're not clobbered. */ /* stop user process cycles */ - mov r0, fp /* first param: caller proc ptr */ - mov fp, #0 /* for stack trace */ + mov r0, fp /* first param: caller proc ptr. */ + mov fp, #0 /* for stack trace. */ bl _C_LABEL(context_stop) pop {r0-r2} /* restore regs */ bl _C_LABEL(do_ipc) /* restore the current process pointer and save the return value */ - pop {fp} /* caller proc ptr */ + pop {fp} /* caller proc ptr. */ str r0, [fp, #REG0] b _C_LABEL(switch_to_user) @@ -240,7 +245,7 @@ ENTRY(restore_user_context) /* Set SPSR and LR for return */ ldr r0, [sp, #PSREG] - msr spsr_fsxc, r0 + msr spsr_fsxc, r0 /* flags , status, extension control. */ ldr lr, [sp, #PCREG] /* Restore user-mode registers from proc struct */ @@ -250,7 +255,7 @@ ENTRY(restore_user_context) ldr sp, [sp] /* To user mode! */ - movs pc, lr + movs pc, lr /* preferred way of returning from svc */ /*===========================================================================*/ /* data */ diff --git a/kernel/arch/earm/protect.c b/kernel/arch/earm/protect.c index 2ea032be7..285d9dd2c 100644 --- a/kernel/arch/earm/protect.c +++ b/kernel/arch/earm/protect.c @@ -75,6 +75,7 @@ int booting_cpu = 0; void prot_init() { + /* tell the HW where we stored our vector table */ write_vbar((reg_t)&exc_vector_table); /* Set up a new post-relocate bootstrap pagetable so that