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x86/x86_64: cleanup signal trampolines 

Let the assembler handle the low-level details of generating .eh_frame,
and use .cfi_escape to output the DWARF3 DW_CFA_def_cfa_expression and
DW_CFA_expression instructions.

Explicitly output a nop instruction between the FDE start
(.cfi_startproc) and the trampoline symbol.

x86_64: remove the rsp instruction, which is redundant with the CFA
itself.

Bug: http://b/169383888
Test: compare `objdump -Wf` output before and after
Test: bionic-unit-tests
Change-Id: Ie2a6d111cb473596be8c9f4fd64534e91d88f2a1
This commit is contained in:
Ryan Prichard 2020-04-17 19:46:51 -07:00
parent bcef897b6d
commit fd8d687051
3 changed files with 172 additions and 143 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

102
libc/arch-x86/bionic/__restore.S
View File

@ -27,14 +27,7 @@
*/
#include <private/bionic_asm.h>
// DWARF constants.
#define DW_CFA_def_cfa_expression 0x0f
#define DW_CFA_expression 0x10
#define DW_EH_PE_pcrel 0x10
#define DW_EH_PE_sdata4 0x0b
#define DW_OP_breg4 0x74
#define DW_OP_deref 0x06
#include <private/bionic_asm_dwarf_exprs.h>
// Offsets into struct sigcontext.
#define OFFSET_EDI 16
@ -52,84 +45,47 @@
#define DW_x86_REG_ECX 1
#define DW_x86_REG_EDX 2
#define DW_x86_REG_EBX 3
#define DW_x86_REG_ESP 4
#define DW_x86_REG_EBP 5
#define DW_x86_REG_ESI 6
#define DW_x86_REG_EDI 7
#define DW_x86_REG_EIP 8
#define cfi_signal_frame_start(f) \
.section .eh_frame,"a",@progbits; \
.L ## f ## _START_EH_FRAME: \
.long 2f - 1f; /* CIE length. */ \
1:.long 0; /* CIE ID. */ \
.byte 1; /* Version. */ \
.string "zRS"; /* Augmentation string. */ \
.uleb128 1; /* Code alignment factor. */ \
.sleb128 -4; /* Data alignment factor. */ \
.uleb128 DW_x86_REG_EIP; /* Return address register. */ \
.uleb128 1; /* 1 byte of augmentation data. */ \
.byte (DW_EH_PE_pcrel|DW_EH_PE_sdata4); /* FDE encoding. */ \
.align 8; \
2: \
.long .L ## f ## _END_FDE - .L ## f ## _START_FDE; /* FDE length. */ \
.L ## f ## _START_FDE: \
.long .L ## f ## _START_FDE - .L ## f ## _START_EH_FRAME; /* CIE location. */ \
.long (.L ## f ## _START - 1) - .; /* pcrel start address (see FDE encoding above). */ \
.long .L ## f ## _END - (.L ## f ## _START - 1); /* Function this FDE applies to. */ \
.uleb128 0; /* FDE augmentation length. */ \
#define RESTORE_GPR(reg, extra_offset) \
m_cfi_breg_offset DW_x86_REG_ ## reg, \
DW_x86_REG_ESP, \
(OFFSET_ ## reg + (extra_offset));
#define cfi_signal_frame_end(f) \
.L ## f ## _END_FDE: \
// Restoring ESP is unnecessary as the unwinder simply uses the CFA value.
#define RESTORE_GPRS(extra_offset) \
m_cfi_def_cfa_deref DW_x86_REG_ESP, (OFFSET_ESP + (extra_offset)); \
RESTORE_GPR(EDI, extra_offset) \
RESTORE_GPR(ESI, extra_offset) \
RESTORE_GPR(EBP, extra_offset) \
RESTORE_GPR(EBX, extra_offset) \
RESTORE_GPR(EDX, extra_offset) \
RESTORE_GPR(ECX, extra_offset) \
RESTORE_GPR(EAX, extra_offset) \
RESTORE_GPR(EIP, extra_offset) \
#define cfi_def_cfa(offset) \
.byte DW_CFA_def_cfa_expression; \
.uleb128 2f-1f; \
1:.byte DW_OP_breg4; \
.sleb128 offset; \
.byte DW_OP_deref; \
2: \
.text
#define cfi_offset(reg_number,offset) \
.byte DW_CFA_expression; \
.uleb128 reg_number; \
.uleb128 2f-1f; \
1:.byte DW_OP_breg4; \
.sleb128 offset; \
2: \
ENTRY_PRIVATE(__restore)
.L__restore_START:
.cfi_startproc
.cfi_signal_frame
RESTORE_GPRS(4)
nop // See comment in libc/arch-x86_64/bionic/__restore_rt.S about this nop.
ENTRY_PRIVATE_NO_DWARF(__restore)
popl %eax
RESTORE_GPRS(0)
movl $__NR_sigreturn, %eax
int $0x80
.L__restore_END:
END(__restore)
cfi_signal_frame_start(__restore)
cfi_def_cfa(OFFSET_ESP + 4)
cfi_offset(DW_x86_REG_EDI, OFFSET_EDI + 4)
cfi_offset(DW_x86_REG_ESI, OFFSET_ESI + 4)
cfi_offset(DW_x86_REG_EBP, OFFSET_EBP + 4)
cfi_offset(DW_x86_REG_EBX, OFFSET_EBX + 4)
cfi_offset(DW_x86_REG_EDX, OFFSET_EDX + 4)
cfi_offset(DW_x86_REG_ECX, OFFSET_ECX + 4)
cfi_offset(DW_x86_REG_EAX, OFFSET_EAX + 4)
cfi_offset(DW_x86_REG_EIP, OFFSET_EIP + 4)
cfi_signal_frame_end(__restore)
ENTRY_PRIVATE(__restore_rt)
.L__restore_rt_START:
.cfi_startproc
.cfi_signal_frame
RESTORE_GPRS(160)
nop // See comment in libc/arch-x86_64/bionic/__restore_rt.S about this nop.
ENTRY_PRIVATE_NO_DWARF(__restore_rt)
movl $__NR_rt_sigreturn, %eax
int $0x80
.L__restore_rt_END:
END(__restore_rt)
cfi_signal_frame_start(__restore_rt)
cfi_def_cfa(OFFSET_ESP + 160)
cfi_offset(DW_x86_REG_EDI, OFFSET_EDI + 160)
cfi_offset(DW_x86_REG_ESI, OFFSET_ESI + 160)
cfi_offset(DW_x86_REG_EBP, OFFSET_EBP + 160)
cfi_offset(DW_x86_REG_EBX, OFFSET_EBX + 160)
cfi_offset(DW_x86_REG_EDX, OFFSET_EDX + 160)
cfi_offset(DW_x86_REG_ECX, OFFSET_ECX + 160)
cfi_offset(DW_x86_REG_EAX, OFFSET_EAX + 160)
cfi_offset(DW_x86_REG_EIP, OFFSET_EIP + 160)
cfi_signal_frame_end(__restore_rt)

112
libc/arch-x86_64/bionic/__restore_rt.S
View File

@ -27,15 +27,9 @@
*/
#include <private/bionic_asm.h>
#include <private/bionic_asm_dwarf_exprs.h>
// DWARF constants.
#define DW_CFA_def_cfa_expression 0x0f
#define DW_CFA_expression 0x10
#define DW_EH_PE_pcrel 0x10
#define DW_EH_PE_sdata4 0x0b
#define DW_OP_breg4 0x74
#define DW_OP_breg7 0x77
#define DW_OP_deref 0x06
// In the signal trampoline frame, rsp points to a ucontext_t struct.
// Offsets into struct ucontext_t of uc_mcontext.gregs[x].
#define OFFSET_R8 40
@ -49,11 +43,11 @@
#define OFFSET_RDI 104
#define OFFSET_RSI 112
#define OFFSET_RBP 120
#define OFFSET_RSP 160
#define OFFSET_RBX 128
#define OFFSET_RDX 136
#define OFFSET_RAX 144
#define OFFSET_RCX 152
#define OFFSET_RSP 160
#define OFFSET_RIP 168
// Non-standard DWARF constants for the x86-64 registers.
@ -75,69 +69,47 @@
#define DW_x86_64_R15 15
#define DW_x86_64_RIP 16
#define cfi_signal_frame_start(f) \
.section .eh_frame,"a",@progbits; \
.L ## f ## _START_EH_FRAME: \
.long 2f - 1f; /* CIE length. */ \
1:.long 0; /* CIE ID. */ \
.byte 1; /* Version. */ \
.string "zRS"; /* Augmentation string. */ \
.uleb128 1; /* Code alignment factor. */ \
.sleb128 -8; /* Data alignment factor. */ \
.uleb128 DW_x86_64_RIP; /* Return address register. */ \
.uleb128 1; /* 1 byte of augmentation data. */ \
.byte (DW_EH_PE_pcrel | DW_EH_PE_sdata4); /* FDE encoding. */ \
.align 8; \
2: \
.long .L ## f ## _END_FDE - .L ## f ## _START_FDE; /* FDE length. */ \
.L ## f ## _START_FDE: \
.long .L ## f ## _START_FDE - .L ## f ## _START_EH_FRAME; /* CIE location. */ \
.long (.L ## f ## _START - 1) - .; /* pcrel start address (see FDE encoding above). */ \
.long .L ## f ## _END - (.L ## f ## _START - 1); /* Function this FDE applies to. */ \
.uleb128 0; /* FDE augmentation length. */ \
// Insert a nop between .cfi_startproc and the trampoline symbol so that unwinders can find the FDE.
// A function's last instruction can be a call instruction (e.g. to __cxa_throw), in which case the
// return address (e.g. from __cxa_throw to the caller) will be just after the function. This
// address may also be the start of the next function, so to avoid ambiguity, unwinders assume that
// a return address PC can refer to the address just after a function, but never to the start of a
// function. (This is implemented by subtracting 1 from the return address PC before looking it up.)
// This is fine for ordinary functions, but breaks on trampolines. Inserting a nop fixes it.
//
// N.B. Unwinders have two other strategies for recognizing the signal trampoline:
// - Read the instructions that the return address PC points at and look for a sigreturn syscall.
// (Hence, the instructions must not change at all.)
// - Do a symbol table lookup and check that against the PC (e.g. LLDB looks for
// __kernel_rt_sigreturn and __restore_rt.)
// Either way, the nop is needed to avoid ambiguity if the function before the trampoline could end
// with a call.
#define cfi_signal_frame_end(f) \
.L ## f ## _END_FDE: \
#define RESTORE_GPR(reg) m_cfi_breg_offset DW_x86_64_ ## reg, DW_x86_64_RSP, OFFSET_ ## reg;
#define cfi_def_cfa(offset) \
.byte DW_CFA_def_cfa_expression; \
.uleb128 2f-1f; \
1:.byte DW_OP_breg7; \
.sleb128 offset; \
.byte DW_OP_deref; \
2: \
#define cfi_offset(reg_number,offset) \
.byte DW_CFA_expression; \
.uleb128 reg_number; \
.uleb128 2f-1f; \
1:.byte DW_OP_breg7; \
.sleb128 offset; \
2: \
ENTRY_PRIVATE(__restore_rt)
.L__restore_rt_START:
.text
.cfi_startproc
.cfi_signal_frame
m_cfi_def_cfa_deref DW_x86_64_RSP, OFFSET_RSP
RESTORE_GPR(R8)
RESTORE_GPR(R9)
RESTORE_GPR(R10)
RESTORE_GPR(R11)
RESTORE_GPR(R12)
RESTORE_GPR(R13)
RESTORE_GPR(R14)
RESTORE_GPR(R15)
RESTORE_GPR(RDI)
RESTORE_GPR(RSI)
RESTORE_GPR(RBP)
RESTORE_GPR(RBX)
RESTORE_GPR(RDX)
RESTORE_GPR(RAX)
RESTORE_GPR(RCX)
// Restoring RSP is unnecessary as the unwinder simply uses the CFA value.
RESTORE_GPR(RIP)
nop
ENTRY_PRIVATE_NO_DWARF(__restore_rt)
mov $__NR_rt_sigreturn, %rax
syscall
.L__restore_rt_END:
END(__restore_rt)
cfi_signal_frame_start(__restore_rt)
cfi_def_cfa(OFFSET_RSP)
cfi_offset(DW_x86_64_R8, OFFSET_R8)
cfi_offset(DW_x86_64_R9, OFFSET_R9)
cfi_offset(DW_x86_64_R10, OFFSET_R10)
cfi_offset(DW_x86_64_R11, OFFSET_R11)
cfi_offset(DW_x86_64_R12, OFFSET_R12)
cfi_offset(DW_x86_64_R13, OFFSET_R13)
cfi_offset(DW_x86_64_R14, OFFSET_R14)
cfi_offset(DW_x86_64_R15, OFFSET_R15)
cfi_offset(DW_x86_64_RDI, OFFSET_RDI)
cfi_offset(DW_x86_64_RSI, OFFSET_RSI)
cfi_offset(DW_x86_64_RBP, OFFSET_RBP)
cfi_offset(DW_x86_64_RSP, OFFSET_RSP)
cfi_offset(DW_x86_64_RBX, OFFSET_RBX)
cfi_offset(DW_x86_64_RDX, OFFSET_RDX)
cfi_offset(DW_x86_64_RAX, OFFSET_RAX)
cfi_offset(DW_x86_64_RCX, OFFSET_RCX)
cfi_offset(DW_x86_64_RIP, OFFSET_RIP)
cfi_signal_frame_end(__restore_rt)

101
libc/private/bionic_asm_dwarf_exprs.h Normal file
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@ -0,0 +1,101 @@
/*
* Copyright (C) 2020 The Android Open Source Project
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
// Define assembler macros for generating DWARF CFI instructions that use DWARF expressions.
// Assemblers don't natively support DWARF expressions, so use the C preprocessor and assembler
// macros to lower them to .cfi_escape directives.
//
// Signal trampolines need to use DWARF expressions to record the locations of saved registers,
// because the offsets from the restored SP to the saved registers is variable. e.g. A signal frame
// can have optional FP/SIMD extensions, and there may be extra padding if the interrupted SP wasn't
// aligned.
// DWARF constants.
#define DW_CFA_def_cfa_expression 0x0f
#define DW_CFA_expression 0x10
#define DW_OP_breg0 0x70
#define DW_OP_deref 0x06
// Return the size of a small uleb128 value: either 1 or 2 bytes
#define ULEB128_14BIT_SIZE(val) \
(1 + (((val) > 0x7f) & 1))
// Return the size of a small sleb128 value: either 1 or 2 bytes
#define SLEB128_14BIT_SIZE(val) \
(1 + (((val) < -0x40) & 1) + \
(((val) > 0x3f) & 1) )
// Output a 1 or 2-byte CFI uleb128 absolute value.
.macro m_cfi_uleb128 val
.if (\val) < 0 || (\val) > 0x3fff
.error "m_cfi_uleb128 value is out of range (\val)"
.elseif (\val) > 0x7f
.cfi_escape ((\val) & 0x7f) | 0x80
.cfi_escape (\val) >> 7
.else
.cfi_escape (\val)
.endif
.endm
// Output a 1 or 2-byte CFI sleb128 absolute value.
.macro m_cfi_sleb128 val
.if (\val) < -0x2000 || (\val) > 0x1fff
.error "m_cfi_sleb128 value is out of range (\val)"
.elseif (\val) < -0x40 || (\val) > 0x3f
.cfi_escape ((\val) & 0x7f) | 0x80
.cfi_escape ((\val) >> 7) & 0x7f
.else
.cfi_escape (\val) & 0x7f
.endif
.endm
.macro check_base_reg reg_no
.if (\reg_no) < 0 || (\reg_no) > 31
.error "base register is out of range for DW_OP_breg0..DW_OP_breg31 (\reg_no)"
.endif
.endm
// Set CFA to the expression, *(base_reg + offset)
.macro m_cfi_def_cfa_deref base_reg, offset
check_base_reg (\base_reg)
.cfi_escape DW_CFA_def_cfa_expression
m_cfi_uleb128 (1 + SLEB128_14BIT_SIZE(\offset) + 1) // size of DWARF expression in bytes
.cfi_escape DW_OP_breg0 + (\base_reg) // expr: 1 byte
m_cfi_sleb128 (\offset) // expr: 1 or 2 bytes
.cfi_escape DW_OP_deref // expr: 1 byte
.endm
// Set the address of the register's previous value to the expression, (base_reg + offset)
.macro m_cfi_breg_offset dest_reg, base_reg, offset
check_base_reg (\base_reg)
.cfi_escape DW_CFA_expression
m_cfi_uleb128 (\dest_reg)
m_cfi_uleb128 (1 + SLEB128_14BIT_SIZE(\offset)) // size of DWARF expression in bytes
.cfi_escape DW_OP_breg0 + (\base_reg) // expr: 1 byte
m_cfi_sleb128 (\offset) // expr: 1 or 2 bytes
.endm