How does __TEXT encode address in __DATA?

Session 406 of WWDC 2016 is great! It explains clearly how the iOS application is settled in memory before running, with ASLR and code-signing. The key point is the indirect pointers in __DATA avoid patching the __TEXT, which is required by ASLR but impossible because of code-signing.

There is this one point confusing me, __TEXT still needs to encode address pointing to __DATA segment, though __DATA page address is randomised now.

The answer is quite simple indeed: the offset between __TEXT and __DATA is not changing between runs, the offset is encoded in __TEXT.

In 64bit Mac OS X, it implements as:

movl 0xae(%rip), %edi

iOS ARMv7 generates:

 0000bf9c f240037c movw r3, #0x7c
 0000bfa0 f2c00300 movt r3, #0x0
 0000bfa4     447b add r3, pc  ;$pc(0xbfa8) + 0x7c -> global_var in __DATA

iOS ARMv8 (64) generates:

 0000000100007f2c adrp x8, 1 ; 0x100007000 + 4k*1
 0000000100007f30 add x8, x8, #64 ; +0x40 -> 0x100008040 
                                  ;-> global_var in __DATA

* adrp xd label  mask out lower 12bits of pc then add label<<12 to generate an address.

curl certificate issue

Mac OS X El Capitan, MacPorts, it goes well for so long. And one day, git complains:

 curl: (77) error setting certificate verify locations:
 CAfile: /opt/local/share/curl/curl-ca-bundle.crt
 CApath: none

Easy, update git config system to use ca-bundle.crt found by searching.

 sslcainfo = /opt/local/share/apps/kssl/ca-bundle.crt

Problem sovled.

But, curl itself still complains:

curl --cacert /opt/local/share/apps/kssl/ca-bundle.crt ...

Problem solved again.

But, it is hard to bear the burden of adding such a long argument!

Why did curl ask for the damn file not existed?

curl-config --ca

OK, it seems that’s the value coded in the source. Fortunately, the command will check CURL_CA_BUNDLE environment variable.
Patch the ~/.profile (or .bashrc for bash, .zshrc for zsh…)


The problem is really resolved.

Auto Layout UITableView cell resizing with multi-line UILabel issue in iOS7

There are many blogs and articles talked about this issue and resolution on Internet. But any of them has this or that problems in those solutions. So I took several hours on researches and got a perfect result, at least I think so. 🙂

Thought about device orientation change, table width and cell width will change. And since we are already use Auto Layout here, it is not a good practice to design cell with any implicit width, say, 320. in Interface Builder. Almost all solutions on Internet assumed 320 width implicitly so those solutions would fail on either landscape orientation, or, iPad if the app is a universal app and you use same cell design for both iPhone and iPad.

So, the problem is in [tableView: heightForRowAtIndexPath:] delegate method. This delegate method is required for iOS7 or the app would crash. To return a correct height value of the cell, we need those steps:

  1. Set cell width to table width after loaded the cell from xib.
  2. Set values for widgets including multi-line UILabel inside cell
  3. Call [cell setNeedsLayout] and [cell layoutIfNeeded]. After those 2 calls, system’s layout engine would set correct width for UILabels. Note at this time the label’s preferredMaxLayoutWidth is still zero or any value left from last using so the layout engine cannot wrap lines and adjust label’s frame correctly.
  4. Set label.preferredMacLayoutWidth = CGRectGetWidth(label.frame)
  5. Call [cell setNeedsLayout] and [cell layoutIfNeeded] again. This time labels have correct preferredMaxLayoutWidth and the layout engine would adjust label’s frame correctly
  6. Now you can call [systemLayoutSizeFittingSize:UILayoutFittingCompressedSize] to get correct height.

Solutions on Internet usually don’t do step 1 and 5. In an invariant screen size they can get correct display but they are not a real solution for other cases.

However, from iOS8 there is a simple solution. Apple solved the issue. Just returning UITableViewAutomaticDimension or just not implementing the method will get correct result. But for apps having to maintain compatibility with iOS7, we still have to do something like this.

国内网盘的 API 服务粗览

因为要写一个从云端读取文件的程序, 首先想到的自然就是目前各家火爆的网盘服务了. 于是今天就花了点时间, 逐个看了一下. 当然, 因为是要写程序嘛, 所以网盘是否提供 API 当然就是重点了. 除了 API 之外, 也要能方便地从浏览器访问, 这样程序才有东西可以读, 对吧.

1. 百度云网盘

原来是有开放 API 的, 叫 PCSAPI (个人云服务), 但是现在已经不支持了. 新的移动接入方式在内测中, 只支持 Android, 并且需要申请. 申请表格中需要填写申请者详细信息以及应用本身的信息和下载方式. 申请之后需要审核, 也不知道要审核多久会不会有回应. 另外, 作为一个需要从云端下载文件的应用, 在你云端都还没有让我访问之前, 我怎么可能有应用存在并供你下载?

另外, 这个 android 的 SDK 还需要你在手机上安装了百度云的 app 才能工作.

2. 360 网盘

不支持 API.

3. 微盘

微盘有公开 API 支持, 开发者简单创建应用后即可使用. 很好. 但是微盘有个应用间微盘空间隔离的策略. 也就是任一应用都不能访问别的应用的存储空间, 也不能访问在 web 上访问到的微盘内容. 从 web 微盘页面上, 也看不到应用的存储空间. 这对于要从 web 传文件而应用只是下载的情形就不行了. 当然, 微盘也还是有可以访问全部空间的选择项的, 只不过也需要申请并审核. 不知道要审核多久会不会有回应.

4. 华为网盘

华为 dbank 网盘做得其实也挺早的, 然而华为做云服务好象总是做不好. 目前华为网盘的注册登录界面到处都有 connection reset 的错误, 连正常的注册登录都没法完成, 让人觉得是不是已经没人维护, 准备抛弃了.

5. 腾讯微云

腾讯微云的 API 是夹杂在一堆无关的 QQ API 中间的. 最要命的是, 腾讯注册开发者需要你上传 “手持身份证” 的照片. Why? 实名登记以便跨省?

6. 115 网盘

115 曾经名声响亮. 然而, 打开 115 首页, 赫然要求只能用 115 浏览器登录, 或者用 115 手机 app 扫码才能登录. 我勒个去, 吃相也未免太太太难看了吧?

7. 金山快盘

注册用户时报错 “服务器正在维护中”, 用个第三方帐号登录进去, 对网盘的页面随便做什么操作都会显示 “服务维护中” 的信息. 同样让人觉得是不是没人维护即将关闭了.

8. 酷盘


9. 千易

只支持网页中嵌入上传文件到千易, 以及为上传的文件提供一个下载链接. 没有 API.

10. 七牛

七牛的 API 比较完整. 然而它不是做网盘的, 它是做云存储服务的. 它没有面向普通用户的 web 网盘操作界面.


好象想不出来别的网盘服务了. 国内比较流行知名的面向普通用户的网盘也就这些了吧, 然而, 结果是, 没有一个能够提供方便的 API 供第三方应用使用. 这其实正是你国互联网界的一个缩影, 外表光鲜, 热闹非凡, 内里却都是破棉絮.

Odd behavior in Windows Service status reporting from recent Windows 2008 R2

I have a Windows service program written many year ago and the user asked me to fix an issue that occurs recently in Windows 2008 R2. Indeed it is not a big problem but quite annoying. When the user stops the service, Windows always popup a window showing an error message like “Windows could not stop the […] service on local computer, The service did not return an error.” Damn it! How could you show me an error dialog with no error message?

Google doesn’t have any similar case like this. So I have try this and that, here and there.

OK, everybody knows that kind of experiments are boring and time consuming. So I just expose the answer.

In the service’s control handler codes for SERVICE_CONTROL_STOP, I reported a SERVICE_RUNNING status followed by a SERVICE_STOP status. That works without any problem before, but caused the issue in recent 2008 R2. After I changed the first status reporting to SERVICE_STOP_PENDING, the dialog disappears.

It looks like Windows doesn’t accept SERVICE_RUNNING when it sent to services SERVICE_CONTROL_STOP. But can you show me a clear error message?


Object subscripting in objc

Object scripting what use something other than an integer inside []. For example, dictionary[@”key”] = @”value”

And in generated machine code, it is a call to selector

-(id) objectForKeyedSubscripting:(id)key

An informal protocol named __ARCLiteKeyedSubscripting__ was defined

@protocol __ARCLiteKeyedSubscripting__
– (void)setObject:(id)arg1 forKeyedSubscript:(id)arg2;
– (id)objectForKeyedSubscript:(id)arg1;

Built-in types like NSDictionary already implemented this protocol, which is indeed generated by compiler. For custom types, just implemented those 2 methods and everything will work.

Some license checkpoints in Reveal app.

  1. [IBAAppDelegate applicationDidFinishLaunching:] would call [IBAAppDelegate verifyCodeSignature] to verify code signature of the app to prevent itself from modifications.
  2. [IBATrialModeReminderPresenter shouldShowTrailModeSheet] controls whether trial mode sheet, including quit after trial period expired, would be shown.
  3. [IBAMainWindowController configureTitleBarAccesoryView] will create IBATrialModeReminderTitleBarAccessoryView to shown trial information on window’s title bar.

That’s all.

Make IB designed view work with iCarousel

Oddly, View designed in IB would have FlexibleWidth+FlexibleHeight set in it autoresizingMask, even if you cleared everything in auto resizing box, regardless using AutoLayout or not. The behavior causes that subviews inside item view have wrong positions after transform3D with rotations. In short, item view’s width/height in subviews position/constraints calculation would be calculated as rotated value instead of  preset value, 

The solution is put self.autoresizingMask = 0 to awakeFromNib, easiest? But it took me 1.5 days to find the reason.

Haunted by Apple Dev Account

I used this Apple ID without iDP enrollment to record a tutorial for a while, it stop working suddenly. Fortunately, I logged into the dev center soon and got award the developer account is hanged for unknown reason. After complaining with Apple guys, the account is restored.

But then, “The identity used to sign the executable is no longer valid.” started.

Well, I had never met this error before and I just reset this test device today for troubleshooting something. Maybe, there is some bug when restoring. But devices shows those provision files are all restored. Well, maybe the account restoring caused something weird? Let me try to reset signing id for iOS program, but no luck. And to delete apple id and re-add it didn’t make it, too.

So I opened Keychain Access app to take a look at certificates, well, the developer certificate of this id is marked as revoked. Good, got you!

But, this certificate refused to be deleted! Tried at least three times, it disappeared immediately after delete key pressed and appear back in 1 second! How mad!

When I got calm down, I guess there is something locked that certificate. So logout and re-login, woo la la, it disappeared. Problem solved.

calabash-ios failed with “No frameworks Group found. Aborting.”

I have quick looked many BDD tools and calabash looks right. It is a quite straightforward solution: integrate a http server into iOS project and bridge actions of cucumber step and iOS runtime using accessibility facility. Because predefined steps are quite complete, it is possible just write feature specs in  Gherkin without touching ruby code.

But it is always so struggling to ramp up a new open source technology.  The first try just failed, even with simplest environment, with a brand new simple view project.

Error message explains itself, I need create this Frameworks group in project to let script continue running. Or it just aborted, no target duplicated, no integration.

The interesting part is, it is an issue known for over 1 year: