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// 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
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// 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
#if defined(__x86_64__)
.balign 16, 0x90
#elif defined(__aarch64__)
.balign 4, 0x0
#if defined(__x86_64__)
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).
// 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->
// 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->
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( save floating-point registers.
popq %rbp
#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( save floating-point registers.
#endif // __x86_64__