[Bug gdb/30457] New: Unexpected sign extension during conversions

[Bug gdb/30457] New: Unexpected sign extension during conversions

[tuliom at ascii dot art.br]

https://sourceware.org/bugzilla/show_bug.cgi?id=30457

            Bug ID: 30457
           Summary: Unexpected sign extension during conversions
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: tuliom at ascii dot art.br
  Target Milestone: ---

Reproducer:

$ cat test-gdb-print.c 
#include <stdio.h>

int
main()
{
  unsigned long foo = 0x00007fffffffe8f8;
  unsigned long * bar = &foo;

  printf("*bar = 0x%lx\n", *bar);

  return 0;
}
$ gcc -g test-gdb-print.c
$ gdb a.out
>>> b test-gdb-print.c:9
Breakpoint 1 at 0x401144: file test-gdb-print.c, line 9.
>>> r
>>> p /x *bar
$1 = 0x7fffffffe8f8         <--- OK, this is what we expect.
>>> p /x bar
$2 = 0x7fffffffda40
>>> p /x (unsigned long) *0x7fffffffda40
$3 = 0xffffffffffffe8f8     <--- The value got sign extended.

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[Bug gdb/30457] Unexpected sign extension during conversions

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30457

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tromey at sourceware dot org

--- Comment #1 from Tom Tromey <tromey at sourceware dot org> ---
>>> p /x (unsigned long) *0x7fffffffda40

gdb assumes that if you use "*" on an integer, it's a pointer-to-int.
Maybe arguably a cast on such a dereference should imply a
different pointer type.

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[Bug gdb/30457] Unexpected sign extension during conversions

[schwab@linux-m68k.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30457

--- Comment #2 from Andreas Schwab <schwab@linux-m68k.org> ---
You can use {unsigned long}0x7fffffffda40 to combine the pointer cast with the
dereference.

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