檢查lldb幀堆棧上系統調用的參數

Question

我正在使用Xcode 4.5中的X86_64程序。我在_NSWarnForDrawingImageWithNoCurrentContext上得到警告，並停止在沒有上下文的情況下進行繪圖調用。該調用發生在深層的CALayer/NSView調用中。我想知道這與什麼觀點有關。

#0 0x00007fff9033f823 in _NSWarnForDrawingImageWithNoCurrentContext() 
#1 0x00007fff8ffd2cf3 in -[NSImageRep drawInRect:fromRect:operation:fraction:respectFlipped:hints:]() 
#2 0x00007fff901444ea in -[NSImageRep _newCGImageForProposedRect:context:hints:flipped:]() 
#3 0x00007fff8ffd3acb in -[NSImageRep CGImageForProposedRect:context:hints:]() 
#4 0x00007fff9006be1d in -[NSImageRep CGImageForProposedRect:context:hints:flipped:]() 
#5 0x00007fff900f0346 in -[NSImage _newSnapshotRepForRep:rect:context:processedHints:]() 
#6 0x00007fff900923c8 in -[NSImage _snapshotRepForRep:rect:context:processedHints:]() 
#7 0x00007fff9006bd77 in __48-[NSImage CGImageForProposedRect:context:hints:]_block_invoke_0() 
#8 0x00007fff8ffd14d6 in -[NSImage _usingBestRepresentationForRect:context:hints:body:]() 
#9 0x00007fff9006b9e5 in -[NSImage CGImageForProposedRect:context:hints:]() 
#10 0x00007fff8ff14754 in -[_NSImageLayerContents CA_copyRenderValue]() 
#11 0x00007fff890350c3 in -[CALayer(CALayerPrivate) _copyRenderLayer:layerFlags:commitFlags:]() 
#12 0x00007fff89034a7c in CA::Context::commit_layer(CA::Layer*, unsigned int, unsigned int, void*)() 
#13 0x00007fff890349a4 in CA::Layer::commit_if_needed(CA::Transaction*, void (*)(CA::Layer*, unsigned int, unsigned int, void*), void*)() 
#14 0x00007fff8903492f in CA::Layer::commit_if_needed(CA::Transaction*, void (*)(CA::Layer*, unsigned int, unsigned int, void*), void*)() 
#15 0x00007fff8903492f in CA::Layer::commit_if_needed(CA::Transaction*, void (*)(CA::Layer*, unsigned int, unsigned int, void*), void*)() 
#16 0x00007fff8903492f in CA::Layer::commit_if_needed(CA::Transaction*, void (*)(CA::Layer*, unsigned int, unsigned int, void*), void*)() 
#17 0x00007fff8903492f in CA::Layer::commit_if_needed(CA::Transaction*, void (*)(CA::Layer*, unsigned int, unsigned int, void*), void*)() 
#18 0x00007fff8903492f in CA::Layer::commit_if_needed(CA::Transaction*, void (*)(CA::Layer*, unsigned int, unsigned int, void*), void*)() 
#19 0x00007fff8903492f in CA::Layer::commit_if_needed(CA::Transaction*, void (*)(CA::Layer*, unsigned int, unsigned int, void*), void*)() 
#20 0x00007fff8903492f in CA::Layer::commit_if_needed(CA::Transaction*, void (*)(CA::Layer*, unsigned int, unsigned int, void*), void*)() 
#21 0x00007fff8903492f in CA::Layer::commit_if_needed(CA::Transaction*, void (*)(CA::Layer*, unsigned int, unsigned int, void*), void*)() 
#22 0x00007fff8903492f in CA::Layer::commit_if_needed(CA::Transaction*, void (*)(CA::Layer*, unsigned int, unsigned int, void*), void*)() 
#23 0x00007fff8903492f in CA::Layer::commit_if_needed(CA::Transaction*, void (*)(CA::Layer*, unsigned int, unsigned int, void*), void*)() 
#24 0x00007fff8903492f in CA::Layer::commit_if_needed(CA::Transaction*, void (*)(CA::Layer*, unsigned int, unsigned int, void*), void*)() 
#25 0x00007fff8903492f in CA::Layer::commit_if_needed(CA::Transaction*, void (*)(CA::Layer*, unsigned int, unsigned int, void*), void*)() 
#26 0x00007fff890258d6 in CA::Context::commit_transaction(CA::Transaction*)() 
#27 0x00007fff89025423 in CA::Transaction::commit()() 
#28 0x00007fff9010f032 in -[NSView(NSLayerKitGlue) _drawRectAsLayerTree:]() 
#29 0x00007fff8ffbe35a in -[NSView _drawRect:clip:]() 
#30 0x00007fff8ffbb093 in -[NSView _recursiveDisplayRectIfNeededIgnoringOpacity:isVisibleRect:rectIsVisibleRectForView:topView:]() 
#31 0x00007fff8ffbbb24 in -[NSView _recursiveDisplayRectIfNeededIgnoringOpacity:isVisibleRect:rectIsVisibleRectForView:topView:]() 
#32 0x00007fff8ffba223 in -[NSThemeFrame _recursiveDisplayRectIfNeededIgnoringOpacity:isVisibleRect:rectIsVisibleRectForView:topView:]() 
#33 0x00007fff8ffb5e4d in -[NSView _displayRectIgnoringOpacity:isVisibleRect:rectIsVisibleRectForView:]() 
#34 0x00007fff8ff7fd73 in -[NSView displayIfNeeded]() 
#35 0x00007fff8ff7f2ac in _handleWindowNeedsDisplayOrLayoutOrUpdateConstraints() 
#36 0x00007fff9054a971 in __83-[NSWindow _postWindowNeedsDisplayOrLayoutOrUpdateConstraintsUnlessPostingDisabled]_block_invoke_01208() 

如何找出視圖_drawRect：剪輯：正在呼籲？

我試圖切換到第29幀，然後做一個p/x $arg1但提供了錯誤

error: Couldn't materialize struct: Couldn't read rdi (materialize)

我只找到源代碼，並提交與此相關的錯誤日誌和無法弄清楚什麼它的意思是。任何幫助將不勝感激，因爲這也有助於避免使用過時的調用給出警告的Apple代碼消息。

Answer 1

您可以嘗試使用「register read」命令，如「reg read arg1」，但真正的問題在於rdi是SysV x86_64 ABI的易失性寄存器。這意味着無論何時進行函數調用，rdi的內容都可能被覆蓋而不保存在任何地方。一旦幀29被稱爲幀28，調試器將假定rdi已被覆蓋（幀29可能將其本身作爲arg存儲到幀28），並且將不能檢索幀29已經存在的rdi的先前內容條目。

即使在堆棧中間，名爲「非易失性」或「被保存的被保護」的寄存器也能保證可檢索。在x86_64上，這些包括rbx和r12-r15。如果第29幀使用r12來保存一個變量，調用幀28和幀28想要使用r12，它必須將舊值保存到堆棧，然後在返回到幀29之前恢復該值。調試器知道如何找到這個保存位置，並可以在第29幀中向您顯示r12的內容 - 通過查看第28幀在哪裏保存並檢索值。 （1）在第29幀上放置一個斷點並在該點輸出arg1的值，或者（2）查看第29幀的彙編指令，並查看該函數是否保存了第一個參數在某處（在堆棧上，在非易失性寄存器中），您仍然可以檢查。否則，當你更深層次的28個棧幀時，參數寄存器的內容早已消失。