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[PATCH] RISC-V: properly terminate call chain
- From: Andreas Schwab <schwab at suse dot de>
- To: libc-alpha at sourceware dot org
- Date: Thu, 25 Oct 2018 11:53:44 +0200
- Subject: [PATCH] RISC-V: properly terminate call chain
Mark the ra register as undefined in _start, so that unwinding through
main works correctly. Also, don't use a tail call so that ra points after
the call to __libc_start_main, not after the previous call.
[BZ #23125]
* sysdeps/riscv/start.S (ENTRY_POINT): Mark ra as undefined.
Don't use tail call.
* elf/tst-unwind-main.c: New file.
* elf/Makefile (tests): Add tst-unwind-main.
(CFLAGS-tst-unwind-main.c): Define.
---
elf/Makefile | 4 +++-
elf/tst-unwind-main.c | 38 ++++++++++++++++++++++++++++++++++++++
sysdeps/riscv/start.S | 7 ++++++-
3 files changed, 47 insertions(+), 2 deletions(-)
create mode 100644 elf/tst-unwind-main.c
diff --git a/elf/Makefile b/elf/Makefile
index 455ec730fc..d277d34b17 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -187,7 +187,7 @@ tests += restest1 preloadtest loadfail multiload origtest resolvfail \
tst-nodelete2 tst-audit11 tst-audit12 tst-dlsym-error tst-noload \
tst-latepthread tst-tls-manydynamic tst-nodelete-dlclose \
tst-debug1 tst-main1 tst-absolute-sym tst-absolute-zero tst-big-note \
- tst-unwind-ctor
+ tst-unwind-ctor tst-unwind-main
# reldep9
tests-internal += loadtest unload unload2 circleload1 \
neededtest neededtest2 neededtest3 neededtest4 \
@@ -1495,3 +1495,5 @@ $(objpfx)tst-libc_dlvsym-static.out: $(objpfx)tst-libc_dlvsym-dso.so
$(objpfx)tst-big-note: $(objpfx)tst-big-note-lib.so
$(objpfx)tst-unwind-ctor: $(objpfx)tst-unwind-ctor-lib.so
+
+CFLAGS-tst-unwind-main.c += -funwind-tables
diff --git a/elf/tst-unwind-main.c b/elf/tst-unwind-main.c
new file mode 100644
index 0000000000..d1236032d7
--- /dev/null
+++ b/elf/tst-unwind-main.c
@@ -0,0 +1,38 @@
+/* Test unwinding through main.
+ Copyright (C) 2018 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library 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
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+#include <unwind.h>
+#include <unistd.h>
+#include <support/test-driver.h>
+
+static _Unwind_Reason_Code
+callback (struct _Unwind_Context *ctx, void *arg)
+{
+ return _URC_NO_REASON;
+}
+
+int
+main (void)
+{
+ /* Arrange for this test to be killed if _Unwind_Backtrace runs into an
+ endless loop. We cannot use the test driver because the complete
+ call chain needs to be compiled with -funwind-tables so that
+ _Unwind_Backtrace is able to reach _start. */
+ alarm (DEFAULT_TIMEOUT);
+ _Unwind_Backtrace (callback, 0);
+}
diff --git a/sysdeps/riscv/start.S b/sysdeps/riscv/start.S
index 4635ddb5eb..ba3e2cf16c 100644
--- a/sysdeps/riscv/start.S
+++ b/sysdeps/riscv/start.S
@@ -43,6 +43,10 @@
__libc_start_main wants this in a5. */
ENTRY (ENTRY_POINT)
+ /* Terminate call stack by noting ra is undefined. Use a dummy
+ .cfi_label to force starting the FDE. */
+ .cfi_label .Ldummy
+ cfi_undefined (ra)
call .Lload_gp
mv a5, a0 /* rtld_fini. */
/* main may be in a shared library. */
@@ -54,7 +58,8 @@ ENTRY (ENTRY_POINT)
lla a4, __libc_csu_fini
mv a6, sp /* stack_end. */
- tail __libc_start_main@plt
+ call __libc_start_main@plt
+ unimp
END (ENTRY_POINT)
/* Dynamic links need the global pointer to be initialized prior to calling
--
2.19.1
--
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE 1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."