PING: [PATCH 2/2] tests/tcg/s390x: Test unwinding from signal handlers

[Ilya Leoshkevich <iii@linux.ibm.com>]

On Wed, 2022-05-04 at 00:51 +0200, Ilya Leoshkevich wrote:
> Add a small test to prevent regressions.
> 
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
>  tests/tcg/s390x/signals-s390x.c | 69 ++++++++++++++++++++++++++-----
> --
>  1 file changed, 55 insertions(+), 14 deletions(-)
> 
> diff --git a/tests/tcg/s390x/signals-s390x.c
> b/tests/tcg/s390x/signals-s390x.c
> index dc2f8ee59a..48c3b6cdfd 100644
> --- a/tests/tcg/s390x/signals-s390x.c
> +++ b/tests/tcg/s390x/signals-s390x.c
> @@ -1,4 +1,5 @@
>  #include <assert.h>
> +#include <execinfo.h>
>  #include <signal.h>
>  #include <string.h>
>  #include <sys/mman.h>
> @@ -11,22 +12,28 @@
>   * inline asm is used instead.
>   */
>  
> +#define DEFINE_ASM_FUNCTION(name, body) \
> +    asm(".globl " #name "\n" \
> +        #name ":\n" \
> +        ".cfi_startproc\n" \
> +        body "\n" \
> +        "br %r14\n" \
> +        ".cfi_endproc");
> +
>  void illegal_op(void);
> -void after_illegal_op(void);
> -asm(".globl\tillegal_op\n"
> -    "illegal_op:\t.byte\t0x00,0x00\n"
> -    "\t.globl\tafter_illegal_op\n"
> -    "after_illegal_op:\tbr\t%r14");
> +extern const char after_illegal_op;
> +DEFINE_ASM_FUNCTION(illegal_op,
> +    ".byte 0x00,0x00\n"
> +    ".globl after_illegal_op\n"
> +    "after_illegal_op:")
>  
>  void stg(void *dst, unsigned long src);
> -asm(".globl\tstg\n"
> -    "stg:\tstg\t%r3,0(%r2)\n"
> -    "\tbr\t%r14");
> +DEFINE_ASM_FUNCTION(stg, "stg %r3,0(%r2)")
>  
>  void mvc_8(void *dst, void *src);
> -asm(".globl\tmvc_8\n"
> -    "mvc_8:\tmvc\t0(8,%r2),0(%r3)\n"
> -    "\tbr\t%r14");
> +DEFINE_ASM_FUNCTION(mvc_8, "mvc 0(8,%r2),0(%r3)")
> +
> +extern const char return_from_main_1;
>  
>  static void safe_puts(const char *s)
>  {
> @@ -49,8 +56,9 @@ static struct {
>  
>  static void handle_signal(int sig, siginfo_t *info, void *ucontext)
>  {
> +    int err, i, n_frames;
> +    void *frames[16];
>      void *page;
> -    int err;
>  
>      if (sig != expected.sig) {
>          safe_puts("[  FAILED  ] wrong signal");
> @@ -86,6 +94,17 @@ static void handle_signal(int sig, siginfo_t
> *info, void *ucontext)
>      default:
>          break;
>      }
> +
> +    n_frames = backtrace(frames, sizeof(frames) /
> sizeof(frames[0]));
> +    for (i = 0; i < n_frames; i++) {
> +        if (frames[i] == &return_from_main_1) {
> +            break;
> +        }
> +    }
> +    if (i == n_frames) {
> +        safe_puts("[  FAILED  ] backtrace() is broken");
> +        _exit(1);
> +    }
>  }
>  
>  static void check_sigsegv(void *func, enum exception exception,
> @@ -122,7 +141,7 @@ static void check_sigsegv(void *func, enum
> exception exception,
>      assert(err == 0);
>  }
>  
> -int main(void)
> +int main_1(void)
>  {
>      struct sigaction act;
>      int err;
> @@ -138,7 +157,7 @@ int main(void)
>      safe_puts("[ RUN      ] Operation exception");
>      expected.sig = SIGILL;
>      expected.addr = illegal_op;
> -    expected.psw_addr = (unsigned long)after_illegal_op;
> +    expected.psw_addr = (unsigned long)&after_illegal_op;
>      expected.exception = exception_operation;
>      illegal_op();
>      safe_puts("[       OK ]");
> @@ -163,3 +182,25 @@ int main(void)
>  
>      _exit(0);
>  }
> +
> +/*
> + * Define main() in assembly in order to test that unwinding from
> signal
> + * handlers until main() works. This way we can define a specific
> point that
> + * the unwinder should reach. This is also better than defining
> main() in C
> + * and using inline assembly to call main_1(), since it's not easy
> to get all
> + * the clobbers right.
> + */
> +
> +DEFINE_ASM_FUNCTION(main,
> +    "stmg %r14,%r15,112(%r15)\n"
> +    ".cfi_offset 14,-48\n"
> +    ".cfi_offset 15,-40\n"
> +    "lay %r15,-160(%r15)\n"
> +    ".cfi_def_cfa_offset 320\n"
> +    "brasl %r14,main_1\n"
> +    ".globl return_from_main_1\n"
> +    "return_from_main_1:\n"
> +    "lmg %r14,%r15,272(%r15)\n"
> +    ".cfi_restore 15\n"
> +    ".cfi_restore 14\n"
> +    ".cfi_def_cfa_offset 160");

Ping.