third_party/ulib/musl/src/setjmp/x86_64/longjmp.S

// Copyright 2017 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "asm.h"
#include "setjmp_impl.h"
#include <zircon/tls.h>

#define DW_CFA_expression       0x10
#define DW_CFA_val_expression   0x16
#define DW_OP_breg0             0x70
#define DW_OP_breg2             (DW_OP_breg0 + 2)
#define DW_OP_breg5             (DW_OP_breg0 + 5)
#define DW_OP_breg7             (DW_OP_breg0 + 7)
#define DW_OP_deref             0x06

// CFI to find regno at 8*index(%rdi).
.macro jb_cfi regno, index
    .if 8 * \index < 0x7f
    .cfi_escape DW_CFA_expression, \regno, 2, DW_OP_breg5, 8 * \index
    .else
    .error "offset too large for one-byte SLEB128"
    .endif
.endm

.macro restore reg, index
    mov 8*\index(%rdi), \reg
    .cfi_same_value \reg
.endm

ENTRY(longjmp)

    // The sanitizer runtime wants to be informed of non-local exits.
    // Call __asan_handle_no_return() before doing the actual longjmp.
#if __has_feature(address_sanitizer)
    // Save our incoming argument registers on the stack around calling
    // __asan_handle_no_return.  The incoming stack is misaligned by one
    // word, so we need to move the stack by an odd number of words,
    // hence the unnecessary save/restore of %rax.
    push_reg %rax
    push_reg %rsi
    push_reg %rdi
    call __asan_handle_no_return@PLT
    pop_reg %rdi
    pop_reg %rsi
    pop_reg %rax
#endif

    // Calculate return value: %r11d = %esi ?: 1
    mov $1, %r11d
    test %esi, %esi
    cmovnz %esi, %r11d

    // Load the mangled values into temporaries.
    mov 8*JB_PC(%rdi), %rax
    .cfi_undefined %rax
    mov 8*JB_SP(%rdi), %rcx
    mov 8*JB_FP(%rdi), %rdx
    mov 8*JB_USP(%rdi), %rsi
    .cfi_undefined %rsi

    // Demangle each temporary.
    xor __setjmp_manglers+8*JB_PC(%rip), %rax
    xor __setjmp_manglers+8*JB_SP(%rip), %rcx
    xor __setjmp_manglers+8*JB_FP(%rip), %rdx
    xor __setjmp_manglers+8*JB_USP(%rip), %rsi

    // The next instruction clobbers the state of longjmp's caller.
    // So from here on, we'll use CFI that unwinds to setjmp's caller instead.
    // Both callers have the same %rdi value, which we're still using.
    .cfi_register %rip, %rax
    .cfi_register %rsp, %rcx
    .cfi_register %rbp, %rdx
    //.cfi_register %unsafe_sp, %rsi  -- No DWARF register number for it!
    jb_cfi 3, JB_RBX
    jb_cfi 12, JB_R12
    jb_cfi 13, JB_R13
    jb_cfi 14, JB_R14
    jb_cfi 15, JB_R15

    // Restore all the vanilla callee-saves registers.
    restore %rbx, JB_RBX
    restore %r12, JB_R12
    restore %r13, JB_R13
    restore %r14, JB_R14
    restore %r15, JB_R15

    // Restore the demangled values.
    mov %rdx, %rbp
    .cfi_same_value %rbp
    mov %rsi, %fs:ZX_TLS_UNSAFE_SP_OFFSET
    //.cfi_same_value %unsafe_sp  -- No DWARF register number for it!
    mov %rax, (%rcx)
    .cfi_escape DW_CFA_expression, 16, 3, DW_OP_breg2, 0, DW_OP_deref

    // Restore SP last.
    // After this, our CFA is setjmp's CFA rather than longjmp's CFA.
    mov %rcx, %rsp
    .cfi_same_value %rsp
    .cfi_escape DW_CFA_expression, 16, 3, DW_OP_breg7, 0, DW_OP_deref

    // Don't leak the demangled values.
    xor %ecx, %ecx
    xor %edx, %edx
    xor %esi, %esi

    mov %r11d, %eax
    ret

END(longjmp)

ALIAS(longjmp, _longjmp)
WEAK_ALIAS(longjmp, siglongjmp)