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-From 4ef64ad1aa9bbbe9471610e2de6ef0c8afed8b1f Mon Sep 17 00:00:00 2001
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-From: Ramin Moussavi <lordrasmus@gmail.com>
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-Date: Wed, 3 Jun 2026 00:00:00 +0200
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-Subject: [PATCH] microblaze: add Linux signal frame unwinding support
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-
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-libgcc has no MD_FALLBACK_FRAME_STATE_FOR for microblaze*-linux*, so the
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-DWARF unwinder cannot step through signal frames at all. Anything that
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-unwinds out of a signal handler -- most prominently NPTL asynchronous
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-pthread cancellation (SIGCANCEL) -- either stops early with
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-_URC_END_OF_STACK (cleanup handlers below the signal frame never run) or
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-misinterprets the on-stack signal trampoline and crashes with SIGSEGV.
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-
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-Add the standard fallback: recognize the two-instruction trampoline the
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-kernel writes into struct rt_sigframe on the stack
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-
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- addik r12, r0, __NR_rt_sigreturn
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- brki r14, 0x8
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-
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-and rebuild the frame state from the sigcontext's pt_regs. The ucontext
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-is anchored relative to the trampoline (its last member) rather than to
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-the CFA, so the layout of the frame head does not matter.
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-
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-The interrupted PC is recorded in DWARF column 36, one past the hard
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-registers, because column 15 must keep the interrupted r15 (unrelated to
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-the resume address of a signal frame). Declaring it as
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-DWARF_ALT_FRAME_RETURN_COLUMN makes init_dwarf_reg_size_table size the
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-column; without that _Unwind_GetGR reads a zero size and aborts.
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-
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-Tested with a microblazeel-linux-uclibc cross compiler against uClibc-ng
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-git, running its NPTL test suite under qemu-system-microblazeel -M
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-petalogix-s3adsp1800. Without the fix 17 tests fail (tst-cancel{1..5,7,
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-9,16,20,x4,x7}, tst-cleanup{1..3}, tst-cond{16,17}) by SIGSEGV or by
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-hanging in the unwinder; with it all 17 pass and the rest of the suite
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-is unchanged. The implementation follows the mips/aarch64
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-linux-unwind.h pattern.
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-
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-gcc/ChangeLog:
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-
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- * config/microblaze/microblaze.h (DWARF_ALT_FRAME_RETURN_COLUMN):
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- Define.
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-
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-libgcc/ChangeLog:
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-
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- * config.host (microblaze*-linux*): Set md_unwind_header.
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- * config/microblaze/linux-unwind.h: New file.
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-
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-Signed-off-by: Ramin Moussavi <ramin.moussavi@yacoub.de>
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-Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>
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----
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- gcc/config/microblaze/microblaze.h | 8 ++
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- libgcc/config.host | 1 +
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- libgcc/config/microblaze/linux-unwind.h | 102 ++++++++++++++++++++++++
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- 3 files changed, 111 insertions(+)
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- create mode 100644 libgcc/config/microblaze/linux-unwind.h
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-
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-diff --git a/gcc/config/microblaze/microblaze.h b/gcc/config/microblaze/microblaze.h
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-index 2b5bd52040f..fc8c4b87175 100644
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---- a/gcc/config/microblaze/microblaze.h
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-+++ b/gcc/config/microblaze/microblaze.h
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-@@ -176,6 +176,14 @@ extern enum pipeline_type microblaze_pipe;
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- #define DWARF_FRAME_RETURN_COLUMN \
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- (GP_REG_FIRST + MB_ABI_SUB_RETURN_ADDR_REGNUM)
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-
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-+/* Signal frames (config/microblaze/linux-unwind.h) record the
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-+ interrupted PC in DWARF column 36, one past the hard registers,
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-+ because column 15 must keep the interrupted r15. Declaring it as
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-+ the alternate return column makes init_dwarf_reg_size_table size
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-+ it; otherwise _Unwind_GetGR aborts when unwinding through a signal
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-+ frame, such as during pthread cancellation. */
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-+#define DWARF_ALT_FRAME_RETURN_COLUMN 36
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-+
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- /* Initial state of return address on entry to func = R15.
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- Actually, the RA is at R15+8, but gcc doesn't know how
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- to generate this.
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-diff --git a/libgcc/config.host b/libgcc/config.host
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-index 046156fa5e7..a685d5da7a1 100644
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---- a/libgcc/config.host
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-+++ b/libgcc/config.host
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-@@ -1050,6 +1050,7 @@ mcore-*-elf)
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- ;;
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- microblaze*-linux*)
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- tmake_file="${tmake_file} microblaze/t-microblaze t-fdpbit t-slibgcc-libgcc"
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-+ md_unwind_header=microblaze/linux-unwind.h
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- ;;
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- microblaze*-*-elf)
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- tmake_file="${tmake_file} microblaze/t-microblaze t-fdpbit"
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-diff --git a/libgcc/config/microblaze/linux-unwind.h b/libgcc/config/microblaze/linux-unwind.h
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-new file mode 100644
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-index 00000000000..b54704a0651
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---- /dev/null
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-+++ b/libgcc/config/microblaze/linux-unwind.h
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-@@ -0,0 +1,102 @@
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-+/* DWARF2 EH unwinding support for MicroBlaze Linux.
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-+ Copyright (C) 2026 Free Software Foundation, Inc.
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-+
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-+ This file is part of GCC.
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-+
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-+ GCC is free software; you can redistribute it and/or modify
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-+ it under the terms of the GNU General Public License as published by
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-+ the Free Software Foundation; either version 3, or (at your option)
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-+ any later version.
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-+
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-+ GCC is distributed in the hope that it will be useful,
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-+ but WITHOUT ANY WARRANTY; without even the implied warranty of
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-+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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-+ GNU General Public License for more details.
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-+
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-+ Under Section 7 of GPL version 3, you are granted additional
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-+ permissions described in the GCC Runtime Library Exception, version
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-+ 3.1, as published by the Free Software Foundation.
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-+
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-+ You should have received a copy of the GNU General Public License and
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-+ a copy of the GCC Runtime Library Exception along with this program;
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-+ see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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-+ <http://www.gnu.org/licenses/>. */
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-+
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-+#ifndef inhibit_libc
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-+
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-+/* Do code reading to identify a signal frame, and set the frame state
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-+ data appropriately. See unwind-dw2.c for the structs. */
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-+
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-+#include <signal.h>
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-+#include <sys/ucontext.h>
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-+#include <asm/unistd.h>
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-+
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-+#define MD_FALLBACK_FRAME_STATE_FOR microblaze_fallback_frame_state
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-+
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-+static _Unwind_Reason_Code
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-+microblaze_fallback_frame_state (struct _Unwind_Context *context,
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-+ _Unwind_FrameState *fs)
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-+{
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-+ const unsigned int *pc = (const unsigned int *) context->ra;
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-+ struct sigcontext *sc;
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-+ _Unwind_Ptr new_cfa;
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-+ int i;
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-+
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-+ /* The outermost frame of a thread may leave a null or near-null
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-+ return address; do not dereference it looking for the
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-+ trampoline. */
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-+ if ((unsigned long) pc < 4096)
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-+ return _URC_END_OF_STACK;
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-+
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-+ /* The kernel writes the signal trampoline onto the stack
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-+ (struct rt_sigframe.tramp):
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-+
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-+ addik r12, r0, __NR_rt_sigreturn
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-+ brki r14, 0x8
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-+
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-+ and sets the saved r15 to the trampoline address minus 8 (the
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-+ handler returns with "rtsd r15, 8"), so the unwound return
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-+ address points 8 bytes before the trampoline. */
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-+ if (pc[0] == (0x31800000 | __NR_rt_sigreturn) && pc[1] == 0xb9cc0008)
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-+ ;
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-+ else if (pc[2] == (0x31800000 | __NR_rt_sigreturn) && pc[3] == 0xb9cc0008)
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-+ pc += 2;
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-+ else
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-+ return _URC_END_OF_STACK;
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-+
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-+ /* The trampoline is the last member of the kernel's rt_sigframe and
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-+ the ucontext sits directly in front of it. Anchor there rather
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-+ than at the CFA so the layout of the frame head does not matter
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-+ (the kernel may insert an ABI argument-home gap at the front).
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-+ uClibc's ucontext_t matches the kernel's struct ucontext. */
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-+ ucontext_t *uc = (ucontext_t *) ((_Unwind_Ptr) pc - sizeof (ucontext_t));
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-+
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-+ sc = (struct sigcontext *) &uc->uc_mcontext;
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-+
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-+ new_cfa = sc->regs.r1;
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-+ fs->regs.cfa_how = CFA_REG_OFFSET;
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-+ fs->regs.cfa_reg = 1; /* r1, the stack pointer. */
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-+ fs->regs.cfa_offset = new_cfa - (_Unwind_Ptr) context->cfa;
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-+
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-+ /* pt_regs holds r0..r31 consecutively. */
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-+ for (i = 0; i < 32; i++)
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-+ {
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-+ fs->regs.how[i] = REG_SAVED_OFFSET;
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-+ fs->regs.reg[i].loc.offset
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-+ = (_Unwind_Ptr) &sc->regs.r0 + i * sizeof (unsigned long) - new_cfa;
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-+ }
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-+
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-+ /* The interrupted PC goes into the alternate return column
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-+ (DWARF_ALT_FRAME_RETURN_COLUMN, defined as 36 in
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-+ gcc/config/microblaze/microblaze.h), one past the hard registers;
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-+ column 15 above keeps the interrupted r15. */
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-+ fs->regs.how[__LIBGCC_DWARF_ALT_FRAME_RETURN_COLUMN__] = REG_SAVED_OFFSET;
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-+ fs->regs.reg[__LIBGCC_DWARF_ALT_FRAME_RETURN_COLUMN__].loc.offset
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-+ = (_Unwind_Ptr) &sc->regs.pc - new_cfa;
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-+ fs->retaddr_column = __LIBGCC_DWARF_ALT_FRAME_RETURN_COLUMN__;
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-+ fs->signal_frame = 1;
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-+
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-+ return _URC_NO_REASON;
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-+}
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-+
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-+#endif
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---
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-2.47.3
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-
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