[Bug translator/17041] New: cast-scope.exp fails on s390x

["jlebon at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=17041

            Bug ID: 17041
           Summary: cast-scope.exp fails on s390x
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: translator
          Assignee: systemtap at sourceware dot org
          Reporter: jlebon at redhat dot com

The cast-scope.exp testcase fails on s390x as follow:

FAIL: cast-scope-m31
line 1: expected "function direct: {._M_dataplus={._M_p="Hello World!"}}"
Got "ERROR: read fault [man error::fault] at 0x000003ff7fbbfe14 (addr) near
identifier '$str' at
../../systemtap/testsuite/systemtap.base/cast-scope.stp:6:59"
    "WARNING: Number of errors: 1, skipped probes: 0"
    "WARNING: /root/systemtap/install/bin/staprun exited with status: 1"
    "Pass 5: run failed.  [man error::pass5]"

Here is cast-scope.cxx:

  1 #include "sys/sdt.h"
  2
  3 #include <string>
  4
  5 size_t
  6 length(const std::string& str)
  7 {
  8     int res, r;
  9     STAP_PROBE1(cast-scope, length, &str);
 10     r = str.length() * 2;
 11     STAP_PROBE(cast-scope, dummy); /* Just here to probe line +5. */
 12     res = r / 2;
 13     STAP_PROBE(cast-scope, dummy2); /* Just here prevent line reordering.
*/
 14     return res;
 15 }
 16
 17 int
 18 main()
 19 {
 20     std::string hello = "Hello World!";
 21     return 12 != length(hello);
 22 }

And here is cast-scope.stp:

  1 global function_string, statement_string, mark_string
  2
  3 probe process.function("length@cast-scope.cxx")
  4 {
  5   function_string .= sprintf("function direct: %s\n", $str$$)
  6   function_string .= sprintf("function cast: %s\n", @cast($str,
"std::string")$$)
  7 }
  8
  9 probe process.statement("length@cast-scope.cxx+4")
 10 {
 11   statement_string .= sprintf("statement direct: %s\n", $str$$)
 12   statement_string .= sprintf("statement cast: %s\n", @cast($str,
"std::string")$$)
 13 }
 14
 15 probe process.mark("length")
 16 {
 17   mark_string .= sprintf("mark cast: %s\n", @cast($arg1, "std::string")$$)
 18 }
 19
 20 probe end
 21 {
 22         # Why print the strings this way? cast-scope.exp expects the
 23         # output in a certain order.  If the probe addresses end up
 24         # the same, the process.function/process.mark probes might get
 25         # called in any order.
 26         #
 27         # So, we'll print the strings in a defined order.
 28         printf("%s", function_string);
 29         printf("%s", mark_string);
 30         printf("%s", statement_string);
 31 }

But even this simple script will fail with the same error:

  1 probe process.function("length@cast-scope.cxx")
  2 {
  3   printf("function cast: %s\n", @cast($str, "std::string")$$)
  4 }

It may be due to a bad calculated address for $str. This is the produced DWARF
code to retrieve $str:

{
  {
    uintptr_t addr;
  uintptr_t frame_base;
  { // DWARF expression: 0x92(11,208)
    {
      uintptr_t s0;
        s0 = fetch_register (11) + 208L;
      frame_base = s0;
    }
  }
    { // DWARF expression: 0x91(-108)
      {
        uintptr_t s0;
        s0 = frame_base + -108L;
        addr = s0;
      }
    }
    { // synthesized
    { uint32_t value = deref (4, addr); addr = value; }
    }
    STAP_RETVALUE = addr;
  }
  goto out;
if (0) goto deref_fault;
deref_fault:
  goto out;
}

So it retrieves the frame_base at register 11 + 208, then retrieves the address
of $str at frame_base - 108.

In comparison, retrieving the string works fine in GDB:

# g++ ../../systemtap/testsuite/systemtap.base/cast-scope.cxx -g -isystem../..
/systemtap/testsuite -isystem/root/systemtap/install/include -m31 -lm -o
cast-scope-m31.exe
# gdb cast-scope-m31.exe
(gdb) break length
Breakpoint 1 at 0x4007f2: file
../../systemtap/testsuite/systemtap.base/cast-scope.cxx, line 9.
(gdb) run
Starting program: /root/systemtap/build/testsuite/cast-scope-m31.exe

Breakpoint 1, length (str="Hello World!") at
../../systemtap/testsuite/systemtap.base/cast-scope.cxx:9
9           STAP_PROBE1(cast-scope, length, &str);
(gdb) print str
$1 = "Hello World!"
(gdb) print str._M_dataplus._M_p
$2 = 0xad4014 "Hello World!"
(gdb) print/x &str
$3 = 0x7fb761f0
(gdb) info regs
Undefined info command: "regs".  Try "help info".
(gdb) info registers
r0             0x0      0
r1             0x477fb761f0     307085402608
r2             0x7fb761f0       2142724592
r3             0x0      0
r4             0x8040086a       2151680106
r5             0x4700000000     304942678016
r6             0x4008fc 4196604
r7             0x7fb76318       2142724888
r8             0x0      0
r9             0x0      0
r10            0x37f    895
r11            0x7fb76120       2142724384
r12            0x4741205000     306035314688
r13            0x400900 4196608
r14            0x804008ac       2151680172
r15            0x7fb76120       2142724384
pc             0x4007f2 0x4007f2 <length(std::string const&)+14>
cc             0x2      2
(gdb)

Note how r11 indicates 0x7fb76120. Which means that to get the address of $str
(at 0x7fb761f0), GDB added to r11: 0x7fb761f0 - 0x7fb76120 = 0xD0 = 208. Doing
the same in SystemTap works:

  1 probe process.function("length@cast-scope.cxx")
  2 {
  3   addr = u_register("r11") + 208
  4   printf("function cast: %s\n", @cast(addr, "std::string")$$)
  5 }

# stap ../../systemtap/testsuite/systemtap.base/cast-scope.stp -c ./cast-scope
-m31.exe
function cast: {._M_dataplus={._M_p="Hello World!"}}
#

So it looks like we're not calculating the address of $str properly.

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