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package/gcc: add microblaze frame unwinding fix to v14

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Add microblaze signal-frame unwinding fix back port to gcc 14.4.0.

Upstream: https://gcc.gnu.org/cgit/gcc/commit/?id=4ef64ad1aa9bbbe9471610e2de6ef0c8afed8b1f

Signed-off-by: Neal Frager <neal.frager@amd.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
This commit is contained in:
Neal Frager
2026-10-14 08:49:08 +01:00
committed by Peter Korsgaard
parent 57f40e5f6e
commit 0e61ae3b5a
1 changed files with 196 additions and 0 deletions
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196
package/gcc/14.4.0/0003-microblaze-add-Linux-signal-frame-unwinding-support.patch Normal file
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@@ -0,0 +1,196 @@
From 4ef64ad1aa9bbbe9471610e2de6ef0c8afed8b1f Mon Sep 17 00:00:00 2001
From: Ramin Moussavi <lordrasmus@gmail.com>
Date: Wed, 3 Jun 2026 00:00:00 +0200
Subject: [PATCH] microblaze: add Linux signal frame unwinding support
libgcc has no MD_FALLBACK_FRAME_STATE_FOR for microblaze*-linux*, so the
DWARF unwinder cannot step through signal frames at all. Anything that
unwinds out of a signal handler -- most prominently NPTL asynchronous
pthread cancellation (SIGCANCEL) -- either stops early with
_URC_END_OF_STACK (cleanup handlers below the signal frame never run) or
misinterprets the on-stack signal trampoline and crashes with SIGSEGV.
Add the standard fallback: recognize the two-instruction trampoline the
kernel writes into struct rt_sigframe on the stack
addik r12, r0, __NR_rt_sigreturn
brki r14, 0x8
and rebuild the frame state from the sigcontext's pt_regs. The ucontext
is anchored relative to the trampoline (its last member) rather than to
the CFA, so the layout of the frame head does not matter.
The interrupted PC is recorded in DWARF column 36, one past the hard
registers, because column 15 must keep the interrupted r15 (unrelated to
the resume address of a signal frame). Declaring it as
DWARF_ALT_FRAME_RETURN_COLUMN makes init_dwarf_reg_size_table size the
column; without that _Unwind_GetGR reads a zero size and aborts.
Tested with a microblazeel-linux-uclibc cross compiler against uClibc-ng
git, running its NPTL test suite under qemu-system-microblazeel -M
petalogix-s3adsp1800. Without the fix 17 tests fail (tst-cancel{1..5,7,
9,16,20,x4,x7}, tst-cleanup{1..3}, tst-cond{16,17}) by SIGSEGV or by
hanging in the unwinder; with it all 17 pass and the rest of the suite
is unchanged. The implementation follows the mips/aarch64
linux-unwind.h pattern.
gcc/ChangeLog:
* config/microblaze/microblaze.h (DWARF_ALT_FRAME_RETURN_COLUMN):
Define.
libgcc/ChangeLog:
* config.host (microblaze*-linux*): Set md_unwind_header.
* config/microblaze/linux-unwind.h: New file.
Upstream: https://gcc.gnu.org/cgit/gcc/commit/?id=4ef64ad1aa9bbbe9471610e2de6ef0c8afed8b1f
Signed-off-by: Ramin Moussavi <ramin.moussavi@yacoub.de>
Signed-off-by: Neal Frager <neal.frager@amd.com>
---
gcc/config/microblaze/microblaze.h | 8 ++
libgcc/config.host | 1 +
libgcc/config/microblaze/linux-unwind.h | 102 ++++++++++++++++++++++++
3 files changed, 111 insertions(+)
create mode 100644 libgcc/config/microblaze/linux-unwind.h
diff --git a/gcc/config/microblaze/microblaze.h b/gcc/config/microblaze/microblaze.h
index 2b5bd52040f7f..fc8c4b8717545 100644
--- a/gcc/config/microblaze/microblaze.h
+++ b/gcc/config/microblaze/microblaze.h
@@ -176,6 +176,14 @@ extern enum pipeline_type microblaze_pipe;
#define DWARF_FRAME_RETURN_COLUMN \
(GP_REG_FIRST + MB_ABI_SUB_RETURN_ADDR_REGNUM)
+/* Signal frames (config/microblaze/linux-unwind.h) record the
+ interrupted PC in DWARF column 36, one past the hard registers,
+ because column 15 must keep the interrupted r15. Declaring it as
+ the alternate return column makes init_dwarf_reg_size_table size
+ it; otherwise _Unwind_GetGR aborts when unwinding through a signal
+ frame, such as during pthread cancellation. */
+#define DWARF_ALT_FRAME_RETURN_COLUMN 36
+
/* Initial state of return address on entry to func = R15.
Actually, the RA is at R15+8, but gcc doesn't know how
to generate this.
diff --git a/libgcc/config.host b/libgcc/config.host
index 046156fa5e786..a685d5da7a107 100644
--- a/libgcc/config.host
+++ b/libgcc/config.host
@@ -1050,6 +1050,7 @@ mcore-*-elf)
;;
microblaze*-linux*)
tmake_file="${tmake_file} microblaze/t-microblaze t-fdpbit t-slibgcc-libgcc"
+ md_unwind_header=microblaze/linux-unwind.h
;;
microblaze*-*-elf)
tmake_file="${tmake_file} microblaze/t-microblaze t-fdpbit"
diff --git a/libgcc/config/microblaze/linux-unwind.h b/libgcc/config/microblaze/linux-unwind.h
new file mode 100644
index 0000000000000..b54704a065198
--- /dev/null
+++ b/libgcc/config/microblaze/linux-unwind.h
@@ -0,0 +1,102 @@
+/* DWARF2 EH unwinding support for MicroBlaze Linux.
+ Copyright (C) 2026 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 or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public 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
+ <http://www.gnu.org/licenses/>. */
+
+#ifndef inhibit_libc
+
+/* Do code reading to identify a signal frame, and set the frame state
+ data appropriately. See unwind-dw2.c for the structs. */
+
+#include <signal.h>
+#include <sys/ucontext.h>
+#include <asm/unistd.h>
+
+#define MD_FALLBACK_FRAME_STATE_FOR microblaze_fallback_frame_state
+
+static _Unwind_Reason_Code
+microblaze_fallback_frame_state (struct _Unwind_Context *context,
+ _Unwind_FrameState *fs)
+{
+ const unsigned int *pc = (const unsigned int *) context->ra;
+ struct sigcontext *sc;
+ _Unwind_Ptr new_cfa;
+ int i;
+
+ /* The outermost frame of a thread may leave a null or near-null
+ return address; do not dereference it looking for the
+ trampoline. */
+ if ((unsigned long) pc < 4096)
+ return _URC_END_OF_STACK;
+
+ /* The kernel writes the signal trampoline onto the stack
+ (struct rt_sigframe.tramp):
+
+ addik r12, r0, __NR_rt_sigreturn
+ brki r14, 0x8
+
+ and sets the saved r15 to the trampoline address minus 8 (the
+ handler returns with "rtsd r15, 8"), so the unwound return
+ address points 8 bytes before the trampoline. */
+ if (pc[0] == (0x31800000 | __NR_rt_sigreturn) && pc[1] == 0xb9cc0008)
+ ;
+ else if (pc[2] == (0x31800000 | __NR_rt_sigreturn) && pc[3] == 0xb9cc0008)
+ pc += 2;
+ else
+ return _URC_END_OF_STACK;
+
+ /* The trampoline is the last member of the kernel's rt_sigframe and
+ the ucontext sits directly in front of it. Anchor there rather
+ than at the CFA so the layout of the frame head does not matter
+ (the kernel may insert an ABI argument-home gap at the front).
+ uClibc's ucontext_t matches the kernel's struct ucontext. */
+ ucontext_t *uc = (ucontext_t *) ((_Unwind_Ptr) pc - sizeof (ucontext_t));
+
+ sc = (struct sigcontext *) &uc->uc_mcontext;
+
+ new_cfa = sc->regs.r1;
+ fs->regs.cfa_how = CFA_REG_OFFSET;
+ fs->regs.cfa_reg = 1; /* r1, the stack pointer. */
+ fs->regs.cfa_offset = new_cfa - (_Unwind_Ptr) context->cfa;
+
+ /* pt_regs holds r0..r31 consecutively. */
+ for (i = 0; i < 32; i++)
+ {
+ fs->regs.how[i] = REG_SAVED_OFFSET;
+ fs->regs.reg[i].loc.offset
+ = (_Unwind_Ptr) &sc->regs.r0 + i * sizeof (unsigned long) - new_cfa;
+ }
+
+ /* The interrupted PC goes into the alternate return column
+ (DWARF_ALT_FRAME_RETURN_COLUMN, defined as 36 in
+ gcc/config/microblaze/microblaze.h), one past the hard registers;
+ column 15 above keeps the interrupted r15. */
+ fs->regs.how[__LIBGCC_DWARF_ALT_FRAME_RETURN_COLUMN__] = REG_SAVED_OFFSET;
+ fs->regs.reg[__LIBGCC_DWARF_ALT_FRAME_RETURN_COLUMN__].loc.offset
+ = (_Unwind_Ptr) &sc->regs.pc - new_cfa;
+ fs->retaddr_column = __LIBGCC_DWARF_ALT_FRAME_RETURN_COLUMN__;
+ fs->signal_frame = 1;
+
+ return _URC_NO_REASON;
+}
+
+#endif