diff options
Diffstat (limited to 'arch/arm64/kernel/start.S')
| -rw-r--r-- | arch/arm64/kernel/start.S | 86 |
1 files changed, 77 insertions, 9 deletions
diff --git a/arch/arm64/kernel/start.S b/arch/arm64/kernel/start.S index 969830d..6ee9941 100644 --- a/arch/arm64/kernel/start.S +++ b/arch/arm64/kernel/start.S @@ -14,12 +14,25 @@ .section .text.boot .globl _start _start: + /* code0: branch over the 64 byte Image header to reset */ b reset .balign 8 -.globl _text_base -_text_base: - .quad 0x40000000 +/* + * the arm64 Image header fields, per Documentation/arch/arm64/ + * booting.rst: text_offset 0x08, image_size 0x10, flags 0x18, + * magic 0x38. code0 above branches over all of it. text_offset 0 + * and image_size filled after link by tools/fillsize.py, the + * magic pins it as a proper Image so qemu -kernel enters at + * RAMBASE instead of guessing +0x80000. + */ + .quad 0x0 /* text_offset, 0x08, filled below */ + .quad 0x0 /* image_size, 0x10, filled below */ + .quad 0x0 /* flags, 0x18: LE, 4k pages, unset */ + .quad 0x0 /* reserved 0x20 */ + .quad 0x0 /* reserved 0x28 */ + .quad 0x0 /* reserved 0x30 */ + .quad 0x644d5241 /* magic, 0x38: ARM\x64 */ reset: /* keep the dtb pointer before anything clobbers x0 */ @@ -60,12 +73,14 @@ from_el3: from_el2: /* - * stay at EL2: the kernel wants it for the virtualization - * extensions and hands off from there. everything below scrubs - * the EL2 state so the kernel starts clean. + * scrub the EL2 state and drop to EL1 for the C runtime. the + * semihosting hlt trap is an EL1 service on qemu, calling it + * from EL2 corrupts the return state. the kernel handoff goes + * back to EL2, booting.rst prefers it there, through the + * trampoline in boot.S. */ - /* EL1 will be aarch64 when the kernel drops itself down */ + /* EL1 will be aarch64 */ mov x0, #(1 << 31) /* HCR_EL2.RW = 1 */ msr hcr_el2, x0 @@ -79,7 +94,12 @@ from_el2: msr hstr_el2, xzr msr vpidr_el2, xzr - b mmu_check + /* drop to EL1, SPSR EL1h with DAIF masked */ + mov x0, #0x3c5 + msr spsr_el2, x0 + adr x0, mmu_check + msr elr_el2, x0 + eret mmu_check: /* @@ -289,7 +309,16 @@ exc_sync: mrs x0, esr_el1 mrs x1, far_el1 2: - mov x2, lr + /* x2 = the faulting PC when it is the sync path */ + mrs x4, CurrentEL + lsr x4, x4, #2 + cmp x4, #2 + b.lt 3f + mrs x2, elr_el2 + b 4f +3: + mrs x2, elr_el1 +4: bl exc_report ldp x29, x30, [sp], #16 b park @@ -300,6 +329,45 @@ exc_sync: * the resume point, eret takes it back. */ hvc_from_el1: + /* + * the lower EL sync slot. three arrivals share it: PSCI hvc + * from the kernel (EC 0x16, PSCI id in x0), our own boot + * handoff (hvc with the payload entry in x8), and semihosting + * hlt #0xf000 from the EL1 C runtime (EC 0x14). qemu only + * answers the hlt when it executes at EL2, so the handler + * replays the trap at EL2 and erets home with the result. + */ + mrs x1, esr_el2 + lsr x1, x1, #26 /* EC */ + cmp x1, #0x14 /* HLT from lower EL, semihosting */ + b.eq smh_replay + + /* + * the hvc arrives with either a PSCI function id in x0 (the + * kernel calling) or the boot handoff staging the payload + * entry in x8 and the dtb in x0. PSCI ids have the 0x84/0xc4 + * prefix, a dtb pointer never does. + */ + lsr x1, x0, #24 + cmp x1, #0x84 + b.eq psci_call + cmp x1, #0xc4 + b.eq psci_call + + /* the boot handoff: ELR_EL2 = entry, eret to the payload */ + msr elr_el2, x8 + eret + +smh_replay: + /* + * x0 holds the semihosting syscall number, x1 the parameter + * block, both live in the caller's registers. replay the hlt + * here at EL2 where qemu answers it, then eret back. + */ + hlt #0xf000 + eret + +psci_call: stp x4, x5, [sp, #-16]! stp x6, x7, [sp, #-16]! stp x29, x30, [sp, #-16]! |