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/* DWARF2 exception handling and frame unwinding for Xtensa.
Copyright (C) 1997-2022 Free Software Foundation, Inc.
This file is part of GCC.
GCC is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.
GCC is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
License for more details.
Under Section 7 of GPL version 3, you are granted additional
permissions described in the GCC Runtime Library Exception, version
3.1, as published by the Free Software Foundation.
You should have received a copy of the GNU General Public License and
a copy of the GCC Runtime Library Exception along with this program;
see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
<>. */
#include "tconfig.h"
#include "tsystem.h"
#include "coretypes.h"
#include "tm.h"
#include "libgcc_tm.h"
#include "dwarf2.h"
#include "unwind.h"
#include "unwind-pe.h"
#include "unwind-dw2-fde.h"
#include "unwind-dw2-xtensa.h"
/* The standard CIE and FDE structures work fine for Xtensa but the
variable-size register window save areas are not a good fit for the rest
of the standard DWARF unwinding mechanism. Nor is that mechanism
necessary, since the register save areas are always in fixed locations
in each stack frame. This file is a stripped down and customized version
of the standard DWARF unwinding code. It needs to be customized to have
builtin logic for finding the save areas and also to track the stack
pointer value (besides the CFA) while unwinding since the primary save
area is located below the stack pointer. It is stripped down to reduce
code size and ease the maintenance burden of tracking changes in the
standard version of the code. */
/* This is the register and unwind state for a particular frame. This
provides the information necessary to unwind up past a frame and return
to its caller. */
struct _Unwind_Context
/* Track register window save areas of 4 registers each, instead of
keeping separate addresses for the individual registers. */
_Unwind_Word *reg[4];
void *cfa;
void *sp;
void *ra;
/* Cache the 2 high bits to replace the window size in return addresses. */
_Unwind_Word ra_high_bits;
void *lsda;
struct dwarf_eh_bases bases;
/* Signal frame context. */
#define SIGNAL_FRAME_BIT ((~(_Unwind_Word) 0 >> 1) + 1)
_Unwind_Word flags;
/* 0 for now, can be increased when further fields are added to
struct _Unwind_Context. */
_Unwind_Word version;
/* Read unaligned data from the instruction buffer. */
union unaligned
void *p;
} __attribute__ ((packed));
static void uw_update_context (struct _Unwind_Context *, _Unwind_FrameState *);
static _Unwind_Reason_Code uw_frame_state_for (struct _Unwind_Context *,
_Unwind_FrameState *);
static inline void *
read_pointer (const void *p) { const union unaligned *up = p; return up->p; }
static inline _Unwind_Word
_Unwind_IsSignalFrame (struct _Unwind_Context *context)
return (context->flags & SIGNAL_FRAME_BIT) ? 1 : 0;
static inline void
_Unwind_SetSignalFrame (struct _Unwind_Context *context, int val)
if (val)
context->flags |= SIGNAL_FRAME_BIT;
context->flags &= ~SIGNAL_FRAME_BIT;
/* Get the value of register INDEX as saved in CONTEXT. */
inline _Unwind_Word
_Unwind_GetGR (struct _Unwind_Context *context, int index)
_Unwind_Word *ptr;
ptr = context->reg[index >> 2] + (index & 3);
return *ptr;
/* Get the value of the CFA as saved in CONTEXT. */
_Unwind_GetCFA (struct _Unwind_Context *context)
return (_Unwind_Ptr) context->sp;
/* Overwrite the saved value for register INDEX in CONTEXT with VAL. */
inline void
_Unwind_SetGR (struct _Unwind_Context *context, int index, _Unwind_Word val)
_Unwind_Word *ptr;
ptr = context->reg[index >> 2] + (index & 3);
*ptr = val;
/* Retrieve the return address for CONTEXT. */
inline _Unwind_Ptr
_Unwind_GetIP (struct _Unwind_Context *context)
return (_Unwind_Ptr) context->ra;
/* Retrieve the return address and flag whether that IP is before
or after first not yet fully executed instruction. */
inline _Unwind_Ptr
_Unwind_GetIPInfo (struct _Unwind_Context *context, int *ip_before_insn)
*ip_before_insn = _Unwind_IsSignalFrame (context);
return (_Unwind_Ptr) context->ra;
/* Overwrite the return address for CONTEXT with VAL. */
inline void
_Unwind_SetIP (struct _Unwind_Context *context, _Unwind_Ptr val)
context->ra = (void *) val;
void *
_Unwind_GetLanguageSpecificData (struct _Unwind_Context *context)
return context->lsda;
_Unwind_GetRegionStart (struct _Unwind_Context *context)
return (_Unwind_Ptr) context->bases.func;
void *
_Unwind_FindEnclosingFunction (void *pc)
struct dwarf_eh_bases bases;
const struct dwarf_fde *fde = _Unwind_Find_FDE (pc-1, &bases);
if (fde)
return bases.func;
return NULL;
_Unwind_GetDataRelBase (struct _Unwind_Context *context)
return (_Unwind_Ptr) context->bases.dbase;
_Unwind_GetTextRelBase (struct _Unwind_Context *context)
return (_Unwind_Ptr) context->bases.tbase;
#include "md-unwind-support.h"
/* Extract any interesting information from the CIE for the translation
unit F belongs to. Return a pointer to the byte after the augmentation,
or NULL if we encountered an undecipherable augmentation. */
static const unsigned char *
extract_cie_info (const struct dwarf_cie *cie, struct _Unwind_Context *context,
_Unwind_FrameState *fs)
const unsigned char *aug = cie->augmentation;
const unsigned char *p = aug + strlen ((const char *)aug) + 1;
const unsigned char *ret = NULL;
_uleb128_t utmp;
_sleb128_t stmp;
/* g++ v2 "eh" has pointer immediately following augmentation string,
so it must be handled first. */
if (aug[0] == 'e' && aug[1] == 'h')
fs->eh_ptr = read_pointer (p);
p += sizeof (void *);
aug += 2;
/* Immediately following the augmentation are the code and
data alignment and return address column. */
p = read_uleb128 (p, &utmp);
p = read_sleb128 (p, &stmp);
if (cie->version == 1)
fs->retaddr_column = *p++;
p = read_uleb128 (p, &utmp);
fs->retaddr_column = (_Unwind_Word)utmp;
fs->lsda_encoding = DW_EH_PE_omit;
/* If the augmentation starts with 'z', then a uleb128 immediately
follows containing the length of the augmentation field following
the size. */
if (*aug == 'z')
p = read_uleb128 (p, &utmp);
ret = p + utmp;
fs->saw_z = 1;
/* Iterate over recognized augmentation subsequences. */
while (*aug != '\0')
/* "L" indicates a byte showing how the LSDA pointer is encoded. */
if (aug[0] == 'L')
fs->lsda_encoding = *p++;
aug += 1;
/* "R" indicates a byte indicating how FDE addresses are encoded. */
else if (aug[0] == 'R')
fs->fde_encoding = *p++;
aug += 1;
/* "P" indicates a personality routine in the CIE augmentation. */
else if (aug[0] == 'P')
_Unwind_Ptr personality;
p = read_encoded_value (context, *p, p + 1, &personality);
fs->personality = (_Unwind_Personality_Fn) personality;
aug += 1;
/* "S" indicates a signal frame. */
else if (aug[0] == 'S')
fs->signal_frame = 1;
aug += 1;
/* Otherwise we have an unknown augmentation string.
Bail unless we saw a 'z' prefix. */
return ret;
return ret ? ret : p;
/* Given the _Unwind_Context CONTEXT for a stack frame, look up the FDE for
its caller and decode it into FS. This function also sets the
lsda member of CONTEXT, as it is really information
about the caller's frame. */
static _Unwind_Reason_Code
uw_frame_state_for (struct _Unwind_Context *context, _Unwind_FrameState *fs)
const struct dwarf_fde *fde;
const struct dwarf_cie *cie;
const unsigned char *aug;
int window_size;
_Unwind_Word *ra_ptr;
memset (fs, 0, sizeof (*fs));
context->lsda = 0;
fde = _Unwind_Find_FDE (context->ra + _Unwind_IsSignalFrame (context) - 1,
if (fde == NULL)
_Unwind_Reason_Code reason;
/* Couldn't find frame unwind info for this function. Try a
target-specific fallback mechanism. This will necessarily
not provide a personality routine or LSDA. */
reason = MD_FALLBACK_FRAME_STATE_FOR (context, fs);
if (reason != _URC_END_OF_STACK)
return reason;
/* The frame was not recognized and handled by the fallback function,
but it is not really the end of the stack. Fall through here and
unwind it anyway. */
cie = get_cie (fde);
if (extract_cie_info (cie, context, fs) == NULL)
/* CIE contained unknown augmentation. */
/* Locate augmentation for the fde. */
aug = (const unsigned char *) fde + sizeof (*fde);
aug += 2 * size_of_encoded_value (fs->fde_encoding);
if (fs->saw_z)
_uleb128_t i;
aug = read_uleb128 (aug, &i);
if (fs->lsda_encoding != DW_EH_PE_omit)
_Unwind_Ptr lsda;
aug = read_encoded_value (context, fs->lsda_encoding, aug, &lsda);
context->lsda = (void *) lsda;
/* Check for the end of the stack. This needs to be checked after
the MD_FALLBACK_FRAME_STATE_FOR check for signal frames because
the contents of context->reg[0] are undefined at a signal frame,
and register a0 may appear to be zero. (The return address in
context->ra comes from register a4 or a8). */
ra_ptr = context->reg[0];
if (ra_ptr && *ra_ptr == 0)
/* Find the window size from the high bits of the return address. */
if (ra_ptr)
window_size = (*ra_ptr >> 30) * 4;
window_size = 8;
fs->retaddr_column = window_size;
return _URC_NO_REASON;
static void
uw_update_context_1 (struct _Unwind_Context *context, _Unwind_FrameState *fs)
struct _Unwind_Context orig_context = *context;
_Unwind_Word *sp, *cfa, *next_cfa;
int i;
if (fs->signal_regs)
cfa = (_Unwind_Word *) fs->signal_regs[1];
next_cfa = (_Unwind_Word *) cfa[-3];
for (i = 0; i < 4; i++)
context->reg[i] = fs->signal_regs + (i << 2);
int window_size = fs->retaddr_column >> 2;
sp = (_Unwind_Word *) orig_context.sp;
cfa = (_Unwind_Word *);
next_cfa = (_Unwind_Word *) cfa[-3];
/* Registers a0-a3 are in the save area below sp. */
context->reg[0] = sp - 4;
/* Find the extra save area below next_cfa. */
for (i = 1; i < window_size; i++)
context->reg[i] = next_cfa - 4 * (1 + window_size - i);
/* Remaining registers rotate from previous save areas. */
for (i = window_size; i < 4; i++)
context->reg[i] = orig_context.reg[i - window_size];
context->sp = cfa;
context->cfa = next_cfa;
_Unwind_SetSignalFrame (context, fs->signal_frame);
/* CONTEXT describes the unwind state for a frame, and FS describes the FDE
of its caller. Update CONTEXT to refer to the caller as well. Note
that the lsda member is not updated here, but later in
uw_frame_state_for. */
static void
uw_update_context (struct _Unwind_Context *context, _Unwind_FrameState *fs)
uw_update_context_1 (context, fs);
/* Compute the return address now, since the return address column
can change from frame to frame. */
if (fs->signal_ra != 0)
context->ra = (void *) fs->signal_ra;
context->ra = (void *) ((_Unwind_GetGR (context, fs->retaddr_column)
& XTENSA_RA_FIELD_MASK) | context->ra_high_bits);
static void
uw_advance_context (struct _Unwind_Context *context, _Unwind_FrameState *fs)
uw_update_context (context, fs);
/* Fill in CONTEXT for top-of-stack. The only valid registers at this
level will be the return address and the CFA. */
#define uw_init_context(CONTEXT) \
do \
{ \
__builtin_unwind_init (); \
uw_init_context_1 (CONTEXT, __builtin_dwarf_cfa (), \
__builtin_return_address (0)); \
} \
while (0)
static void __attribute__((noinline))
uw_init_context_1 (struct _Unwind_Context *context, void *outer_cfa,
void *outer_ra)
void *ra = __builtin_return_address (0);
void *cfa = __builtin_dwarf_cfa ();
_Unwind_FrameState fs;
memset (context, 0, sizeof (struct _Unwind_Context));
context->ra = ra;
memset (&fs, 0, sizeof (fs));
fs.retaddr_column = 8;
context->sp = cfa;
context->cfa = outer_cfa;
context->ra_high_bits =
((_Unwind_Word) uw_init_context_1) & ~XTENSA_RA_FIELD_MASK;
uw_update_context_1 (context, &fs);
context->ra = outer_ra;
/* Install TARGET into CURRENT so that we can return to it. This is a
macro because __builtin_eh_return must be invoked in the context of
our caller, and also because spilling registers of the caller before
the context installation may result in reload of wrong register values
after the context installation due to the change of the stack pointer
in the base save area. This spilling may be caused by an interrupt
handler on baremetal host. */
#define uw_install_context(CURRENT, TARGET, FRAMES) \
do \
{ \
void *handler = __builtin_frob_return_addr ((TARGET)->ra); \
long i; \
/* The eh_return insn assumes a window size of 8, so don't bother \
copying the save areas for registers a8-a15 since they won't be \
reloaded. */ \
for (i = 0; i < 2; ++i) \
{ \
_Unwind_Word *c = (CURRENT)->reg[i]; \
_Unwind_Word *t = (TARGET)->reg[i]; \
int j; \
if (t && c && t != c) \
for (j = 0; j < 4; ++j) \
*c++ = *t++; \
} \
__builtin_eh_return (0, handler); \
} \
while (0)
static inline _Unwind_Ptr
uw_identify_context (struct _Unwind_Context *context)
return _Unwind_GetCFA (context);
#include ""
#if defined (USE_GAS_SYMVER) && defined (SHARED) && defined (USE_LIBUNWIND_EXCEPTIONS)
alias (_Unwind_Backtrace);
alias (_Unwind_DeleteException);
alias (_Unwind_FindEnclosingFunction);
alias (_Unwind_ForcedUnwind);
alias (_Unwind_GetDataRelBase);
alias (_Unwind_GetTextRelBase);
alias (_Unwind_GetCFA);
alias (_Unwind_GetGR);
alias (_Unwind_GetIP);
alias (_Unwind_GetLanguageSpecificData);
alias (_Unwind_GetRegionStart);
alias (_Unwind_RaiseException);
alias (_Unwind_Resume);
alias (_Unwind_Resume_or_Rethrow);
alias (_Unwind_SetGR);
alias (_Unwind_SetIP);