winedbg: output of the bt command misses sometimes a frame
Hello, as I was debugging in wine I wondered if following behaviour is intended or could be considered a bug (and should be filed in bugtracker?). When the debugger's current position is on the opening curly bracket of a function a "bt" command writes a different stack as if the current position is on the next instruction in this function. What me makes wonder is the frame 0 is always correct but the calling function is not in the stack at all in the first bt: Wine-dbg>bt Backtrace: =>0 0x7ebe3622 IsWindow(hwnd=0x20060) [/home/bernhard/data/entwicklung/2010/wine/wine-git/dlls/user32/win.c:2503] in user32 (0x0033b500) 1 0x7e25429d create_window16+0x5c(cs=0x33b53c, className="QWidget", instance=0x400000, unicode=1) [/home/bernhard/data/entwicklung/2010/wine/wine-git/dlls/user.exe16/message.c:2670] in user.exe16 (0x0033b520) 2 0x7ebe0f91 CreateWindowExW+0x7e(exStyle=1024, className="QWidget", windowName="pica", style=114032640, x=-2147483648, y=-2147483648, width=-2147483648, height=-2147483648, parent=(nil), menu=(nil), instance=0x400000, data=0x0(nil)) [/home/bernhard/data/entwicklung/2010/wine/wine-git/dlls/user32/win.c:1500] in user32 (0x0033b570) 3 0x650778f3 in qtgui4 (+0x778f3) (0x80000000) Wine-dbg>next 2507 if (!(ptr = WIN_GetPtr( hwnd ))) return FALSE; Wine-dbg>bt Backtrace: =>0 0x7ebe3637 IsWindow+0x15(hwnd=0x20060) [/home/bernhard/data/entwicklung/2010/wine/wine-git/dlls/user32/win.c:2507] in user32 (0x0033b2b0) 1 0x7ebe0bda WIN_CreateWindowEx+0x1201(cs=0x33b53c, className="QWidget", module=0x400000, unicode=1) [/home/bernhard/data/entwicklung/2010/wine/wine-git/dlls/user32/win.c:1406] in user32 (0x0033b500) 2 0x7e25429d create_window16+0x5c(cs=0x33b53c, className="QWidget", instance=0x400000, unicode=1) [/home/bernhard/data/entwicklung/2010/wine/wine-git/dlls/user.exe16/message.c:2670] in user.exe16 (0x0033b520) 3 0x7ebe0f91 CreateWindowExW+0x7e(exStyle=1024, className="QWidget", windowName="pica", style=114032640, x=-2147483648, y=-2147483648, width=-2147483648, height=-2147483648, parent=(nil), menu=(nil), instance=0x400000, data=0x0(nil)) [/home/bernhard/data/entwicklung/2010/wine/wine-git/dlls/user32/win.c:1500] in user32 (0x0033b570) 4 0x650778f3 in qtgui4 (+0x778f3) (0x80000000) Wine-dbg> Kind regards Bernhard
Bernhard Übelacker a écrit :
Hello, as I was debugging in wine I wondered if following behaviour is intended or could be considered a bug (and should be filed in bugtracker?).
When the debugger's current position is on the opening curly bracket of a function a "bt" command writes a different stack as if the current position is on the next instruction in this function.
What me makes wonder is the frame 0 is always correct but the calling function is not in the stack at all in the first bt:
this is likely because the prolog of IsWindow hasn't been run yet try next (while on first { and you should get a decent backtrace actually, on i386, at the point you're considering eip : is already in new function but stack (ebp, esp) hasn't been initialized yet to new function => the prolog does it actually, this is mainly due to the fact that winedbg doesn't do lots of magic about guessing prolog size, except when debug information is PDB (in that case, this very information is in the debug format) we used to do some weird heuristics... like setting break address for function foo at second line number for this function, which is wrong of course real fix would be (as gdb does in some cases) to disassembly the first bytes of the functions to guess the prolog size A+ -- Eric Pouech "The problem with designing something completely foolproof is to underestimate the ingenuity of a complete idiot." (Douglas Adams)
--- On Sat, 6/2/10, Bernhard Übelacker <bernhardu(a)vr-web.de> wrote:
Hello, as I was debugging in wine I wondered if following behaviour is intended or could be considered a bug (and should be filed in bugtracker?).
When the debugger's current position is on the opening curly bracket of a function a "bt" command writes a different stack as if the current position is on the next instruction in this function.
I think you mis-understand how compiler and debugger works. Curly brackets delimit blocks of code but do not correspond to any machine instructions themselves, and is hence removed during compilation and execution. So debuggers are supposed to skip over them and behaves as if they don't exist during code inspection.
What me makes wonder is the frame 0 is always correct but the calling function is not in the stack at all in the first bt:
Wine-dbg>bt Backtrace: =>0 0x7ebe3622 IsWindow(hwnd=0x20060) [/home/bernhard/data/entwicklung/2010/wine/wine-git/dlls/user32/win.c:2503] in user32 (0x0033b500) 1 0x7e25429d create_window16+0x5c(cs=0x33b53c, className="QWidget", instance=0x400000, unicode=1) [/home/bernhard/data/entwicklung/2010/wine/wine-git/dlls/user.exe16/message.c:2670] in user.exe16 (0x0033b520) 2 0x7ebe0f91 CreateWindowExW+0x7e(exStyle=1024, className="QWidget", windowName="pica", style=114032640, x=-2147483648, y=-2147483648, width=-2147483648, height=-2147483648, parent=(nil), menu=(nil), instance=0x400000, data=0x0(nil)) [/home/bernhard/data/entwicklung/2010/wine/wine-git/dlls/user32/win.c:1500] in user32 (0x0033b570) 3 0x650778f3 in qtgui4 (+0x778f3) (0x80000000)
Wine-dbg>next 2507 if (!(ptr = WIN_GetPtr( hwnd ))) return FALSE;
Wine-dbg>bt Backtrace: =>0 0x7ebe3637 IsWindow+0x15(hwnd=0x20060) [/home/bernhard/data/entwicklung/2010/wine/wine-git/dlls/user32/win.c:2507] in user32 (0x0033b2b0) 1 0x7ebe0bda WIN_CreateWindowEx+0x1201(cs=0x33b53c, className="QWidget", module=0x400000, unicode=1) [/home/bernhard/data/entwicklung/2010/wine/wine-git/dlls/user32/win.c:1406] in user32 (0x0033b500) 2 0x7e25429d create_window16+0x5c(cs=0x33b53c, className="QWidget", instance=0x400000, unicode=1) [/home/bernhard/data/entwicklung/2010/wine/wine-git/dlls/user.exe16/message.c:2670] in user.exe16 (0x0033b520) 3 0x7ebe0f91 CreateWindowExW+0x7e(exStyle=1024, className="QWidget", windowName="pica", style=114032640, x=-2147483648, y=-2147483648, width=-2147483648, height=-2147483648, parent=(nil), menu=(nil), instance=0x400000, data=0x0(nil)) [/home/bernhard/data/entwicklung/2010/wine/wine-git/dlls/user32/win.c:1500] in user32 (0x0033b570) 4 0x650778f3 in qtgui4 (+0x778f3) (0x80000000)
Wine-dbg>
Kind regards Bernhard
participants (3)
-
Bernhard Übelacker -
Eric Pouech -
Hin-Tak Leung