[Bug 1889411] [NEW] RISC-V: Unable to unwind the stack upon signals

* [Bug 1889411] [NEW] RISC-V: Unable to unwind the stack upon signals
@ 2020-07-29 12:42 Bernhard Urban-Forster
  2020-08-13 22:33 ` [Bug 1889411] " Alistair Francis
                   ` (2 more replies)
  0 siblings, 3 replies; 4+ messages in thread
From: Bernhard Urban-Forster @ 2020-07-29 12:42 UTC (permalink / raw)
  To: qemu-devel

Public bug reported:

Consider the following program:

===============================================================
#include <stdio.h>
#include <stdlib.h>

#define NOINLINE __attribute__ ((noinline))

void NOINLINE abort_me(void) { abort(); /* trigger SIGABRT */ }

void NOINLINE level1(void) { abort_me(); }

void NOINLINE level2(void) { level1(); }

void NOINLINE level3(void) { level2(); }

void NOINLINE level4(void) { level3();}

int main(void) {
	level4();
	return 0;
}
===============================================================

$ riscv64-linux-gnu-gcc -march=rv64imafdc -O0 -g c.c
$ qemu-riscv64 -g 31337 ./c &
$ riscv64-unknown-linux-gnu-gdb -q -ex 'target remote localhost:31337' -ex 'b abort_me' -ex c -ex bt ./c
Reading symbols from c...
Remote debugging using localhost:31337
Reading symbols from /home/lewurm/riscv/sysroot/lib/ld-linux-riscv64-lp64d.so.1...
0x0000004000804f30 in _start () from /home/lewurm/riscv/sysroot/lib/ld-linux-riscv64-lp64d.so.1
Breakpoint 1 at 0x4000000632: file c.c, line 7.
Continuing.

Breakpoint 1, abort_me () at c.c:7
7               abort(); /* trigger SIGABRT */
#0  abort_me () at c.c:7
#1  0x0000004000000642 in level1 () at c.c:11
#2  0x0000004000000658 in level2 () at c.c:15
#3  0x000000400000066e in level3 () at c.c:19
#4  0x0000004000000684 in level4 () at c.c:23
#5  0x000000400000069a in main () at c.c:27
===============================================================

So far so good, I get a proper backtrace as expected. If I let the
signal trigger however, gdb is not able to unwind the stack:

(gdb) c
Continuing.

Program received signal SIGABRT, Aborted.
0x0000004000858074 in ?? ()
(gdb) bt
#0  0x0000004000858074 in ?? ()

I get the same behaviour for SIGSEGV and SIGILL, I didn't try other
signals. Apparently this scenario works on real hardware (see linked gdb
issue below), and presumably it would work with system qemu (I haven't
tested that yet though). So my guess is that qemu does something
differently around signal handling than the linux kernel.

Full reproducer: https://gist.github.com/lewurm/befb9ddf5894bad9628b1df77258598b
RISC-V GDB issue: https://github.com/riscv/riscv-binutils-gdb/issues/223

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1889411

Title:
  RISC-V: Unable to unwind the stack upon signals

Status in QEMU:
  New

Bug description:
  Consider the following program:

  ===============================================================
  #include <stdio.h>
  #include <stdlib.h>

  #define NOINLINE __attribute__ ((noinline))

  void NOINLINE abort_me(void) { abort(); /* trigger SIGABRT */ }

  void NOINLINE level1(void) { abort_me(); }

  void NOINLINE level2(void) { level1(); }

  void NOINLINE level3(void) { level2(); }

  void NOINLINE level4(void) { level3();}

  int main(void) {
  	level4();
  	return 0;
  }
  ===============================================================

  $ riscv64-linux-gnu-gcc -march=rv64imafdc -O0 -g c.c
  $ qemu-riscv64 -g 31337 ./c &
  $ riscv64-unknown-linux-gnu-gdb -q -ex 'target remote localhost:31337' -ex 'b abort_me' -ex c -ex bt ./c
  Reading symbols from c...
  Remote debugging using localhost:31337
  Reading symbols from /home/lewurm/riscv/sysroot/lib/ld-linux-riscv64-lp64d.so.1...
  0x0000004000804f30 in _start () from /home/lewurm/riscv/sysroot/lib/ld-linux-riscv64-lp64d.so.1
  Breakpoint 1 at 0x4000000632: file c.c, line 7.
  Continuing.

  Breakpoint 1, abort_me () at c.c:7
  7               abort(); /* trigger SIGABRT */
  #0  abort_me () at c.c:7
  #1  0x0000004000000642 in level1 () at c.c:11
  #2  0x0000004000000658 in level2 () at c.c:15
  #3  0x000000400000066e in level3 () at c.c:19
  #4  0x0000004000000684 in level4 () at c.c:23
  #5  0x000000400000069a in main () at c.c:27
  ===============================================================

  So far so good, I get a proper backtrace as expected. If I let the
  signal trigger however, gdb is not able to unwind the stack:

  (gdb) c
  Continuing.

  Program received signal SIGABRT, Aborted.
  0x0000004000858074 in ?? ()
  (gdb) bt
  #0  0x0000004000858074 in ?? ()

  I get the same behaviour for SIGSEGV and SIGILL, I didn't try other
  signals. Apparently this scenario works on real hardware (see linked
  gdb issue below), and presumably it would work with system qemu (I
  haven't tested that yet though). So my guess is that qemu does
  something differently around signal handling than the linux kernel.

  Full reproducer: https://gist.github.com/lewurm/befb9ddf5894bad9628b1df77258598b
  RISC-V GDB issue: https://github.com/riscv/riscv-binutils-gdb/issues/223

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