| // Copyright 2018 The Crashpad Authors. All rights reserved. |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| // namespace crashpad { |
| // void CaptureContext(ucontext_t* context); |
| // } // namespace crashpad |
| |
| #define CAPTURECONTEXT_SYMBOL _ZN8crashpad14CaptureContextEP8ucontext |
| |
| .text |
| .globl CAPTURECONTEXT_SYMBOL |
| #if defined(__x86_64__) |
| .balign 16, 0x90 |
| #elif defined(__aarch64__) |
| .balign 4, 0x0 |
| #endif |
| |
| CAPTURECONTEXT_SYMBOL: |
| |
| #if defined(__x86_64__) |
| |
| .cfi_startproc |
| |
| pushq %rbp |
| .cfi_def_cfa_offset 16 |
| .cfi_offset %rbp, -16 |
| movq %rsp, %rbp |
| .cfi_def_cfa_register %rbp |
| |
| // Note that 16-byte stack alignment is not maintained because this function |
| // does not call out to any other. |
| |
| // pushfq first, because some instructions (but probably none used here) |
| // affect %rflags. %rflags will be in -8(%rbp). |
| pushfq |
| |
| // General-purpose registers whose values haven’t changed can be captured |
| // directly. |
| movq %r8, 0x28(%rdi) // context->uc_mcontext.r8 |
| movq %r9, 0x30(%rdi) // context->uc_mcontext.r9 |
| movq %r10, 0x38(%rdi) // context->uc_mcontext.r10 |
| movq %r11, 0x40(%rdi) // context->uc_mcontext.r11 |
| movq %r12, 0x48(%rdi) // context->uc_mcontext.r12 |
| movq %r13, 0x50(%rdi) // context->uc_mcontext.r13 |
| movq %r14, 0x58(%rdi) // context->uc_mcontext.r14 |
| movq %r15, 0x60(%rdi) // context->uc_mcontext.r15 |
| |
| // Because of the calling convention, there’s no way to recover the value of |
| // the caller’s %rdi as it existed prior to calling this function. This |
| // function captures a snapshot of the register state at its return, which |
| // involves %rdi containing a pointer to its first argument. Callers that |
| // require the value of %rdi prior to calling this function should obtain it |
| // separately. For example: |
| // uint64_t rdi; |
| // asm("movq %%rdi, %0" : "=m"(rdi)); |
| movq %rdi, 0x68(%rdi) // context->uc_mcontext.rdi |
| |
| movq %rsi, 0x70(%rdi) // context->uc_mcontext.rsi |
| |
| // Use %r8 as a scratch register now that it has been saved. |
| // The original %rbp was saved on the stack in this function’s prologue. |
| movq (%rbp), %r8 |
| movq %r8, 0x78(%rdi) // context->uc_mcontext.rbp |
| |
| // Save the remaining general-purpose registers. |
| movq %rbx, 0x80(%rdi) // context->uc_mcontext.rbx |
| movq %rdx, 0x88(%rdi) // context->uc_mcontext.rdx |
| movq %rax, 0x90(%rdi) // context->uc_mcontext.rax |
| movq %rcx, 0x98(%rdi) // context->uc_mcontext.rcx |
| |
| // %rsp was saved in %rbp in this function’s prologue, but the caller’s %rsp |
| // is 16 more than this value: 8 for the original %rbp saved on the stack in |
| // this function’s prologue, and 8 for the return address saved on the stack |
| // by the call instruction that reached this function. |
| leaq 16(%rbp), %r8 |
| movq %r8, 0xa0(%rdi) // context->uc_mcontext.rsp |
| |
| // The return address saved on the stack used by the call of this function is |
| // likely more useful than the current RIP here. |
| movq 8(%rbp), %r8 |
| movq %r8, 0xa8(%rdi) // context->uc_mcontext.rip |
| |
| // The original %rflags was saved on the stack above. |
| movq -8(%rbp), %r8 |
| movq %r8, 0xb0(%rdi) // context->uc_mcontext.eflags |
| |
| // Save the segment registers |
| movw %cs, 0xb8(%rdi) // context->uc_mcontext.cs |
| movw %gs, 0xba(%rdi) // context->uc_mcontext.gs |
| movw %fs, 0xbc(%rdi) // context->uc_mcontext.fs |
| |
| xorw %ax, %ax |
| movw %ax, 0xbe(%rdi) // context->uc_mcontext.padding |
| |
| // Zero out the remainder of the unused pseudo-registers |
| xorq %r8, %r8 |
| movq %r8, 0xc0(%rdi) // context->uc_mcontext.err |
| movq %r8, 0xc8(%rdi) // context->uc_mcontext.trapno |
| movq %r8, 0xd0(%rdi) // context->uc_mcontext.oldmask |
| movq %r8, 0xd8(%rdi) // context->uc_mcontext.cr2 |
| |
| // Clean up by restoring clobbered registers, even those considered volatile |
| // by the ABI, so that the captured context represents the state at this |
| // function’s exit. |
| movq 0x90(%rdi), %rax |
| movq 0x28(%rdi), %r8 |
| |
| // TODO(https://crashpad.chromium.org/bug/300): save floating-point registers. |
| |
| popfq |
| |
| popq %rbp |
| |
| ret |
| |
| .cfi_endproc |
| |
| #elif defined(__aarch64__) |
| |
| // Zero out fault_address, which is unused. |
| str x31, [x0, #0xb0] // context->uc_mcontext.fault_address |
| |
| // Save general purpose registers in context->uc_mcontext.regs[i]. |
| // The original x0 can't be recovered. |
| stp x0, x1, [x0, #0xb8] |
| stp x2, x3, [x0, #0xc8] |
| stp x4, x5, [x0, #0xd8] |
| stp x6, x7, [x0, #0xe8] |
| stp x8, x9, [x0, #0xf8] |
| stp x10, x11, [x0, #0x108] |
| stp x12, x13, [x0, #0x118] |
| stp x14, x15, [x0, #0x128] |
| stp x16, x17, [x0, #0x138] |
| stp x18, x19, [x0, #0x148] |
| stp x20, x21, [x0, #0x158] |
| stp x22, x23, [x0, #0x168] |
| stp x24, x25, [x0, #0x178] |
| stp x26, x27, [x0, #0x188] |
| stp x28, x29, [x0, #0x198] |
| |
| // The original LR can't be recovered. |
| str LR, [x0, #0x1a8] |
| |
| // Use x1 as a scratch register. |
| mov x1, SP |
| str x1, [x0, #0x1b0] // context->uc_mcontext.sp |
| |
| // The link register holds the return address for this function. |
| str LR, [x0, #0x1b8] // context->uc_mcontext.pc |
| |
| // pstate should hold SPSR but NZCV are the only bits we know about. |
| mrs x1, NZCV |
| str x1, [x0, #0x1c0] // context->uc_mcontext.pstate |
| |
| // Restore x1 from the saved context. |
| ldr x1, [x0, #0xc0] |
| |
| // TODO(https://crashpad.chromium.org/bug/300): save floating-point registers. |
| |
| ret |
| |
| #endif // __x86_64__ |