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0b8b3ba21e
This is likely only the tip of the ice berg, but this particular bug caused any double-free on a glibc system to turn into a deadlock! It is not generally safe to either allocate or release heap memory from within the signal handler. The 'pop_back()' in RemoveFilesToRemove was deleting memory and causing the deadlock. What's worse, eraseFromDisk in PathV1 has lots of allocation and deallocation paths. We even passed 'true' in a place that would have caused the *signal handler* to try to run the 'system' system call and shell out to 'rm -rf'. That was never going to work... This patch switches the file removal to use a vector of strings so that the exact text needed for the 'unlink' system call can be stored there. It switches the loop to be a boring indexed loop, and directly calls unlink without looking at the error. It also works quite hard to ensure that calling 'c_str()' is safe, by ensuring that the non-signal-handling code path that manipulates the vector always leaves it in a state where every element has already had 'c_str()' called at least once. I dunno exactly how overkill this is, but it fixes the deadlock-on-double free issue, and seems likely to prevent any other issues from sneaking up. Sorry for not having a test case, but I *really* don't know how to test signal handling code easily.... git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158580 91177308-0d34-0410-b5e6-96231b3b80d8
Design Of lib/System
====================
The software in this directory is designed to completely shield LLVM from any
and all operating system specific functionality. It is not intended to be a
complete operating system wrapper (such as ACE), but only to provide the
functionality necessary to support LLVM.
The software located here, of necessity, has very specific and stringent design
rules. Violation of these rules means that cracks in the shield could form and
the primary goal of the library is defeated. By consistently using this library,
LLVM becomes more easily ported to new platforms since the only thing requiring
porting is this library.
Complete documentation for the library can be found in the file:
llvm/docs/SystemLibrary.html
or at this URL:
http://llvm.org/docs/SystemLibrary.html
While we recommend that you read the more detailed documentation, for the
impatient, here's a high level summary of the library's requirements.
1. No system header files are to be exposed through the interface.
2. Std C++ and Std C header files are okay to be exposed through the interface.
3. No exposed system-specific functions.
4. No exposed system-specific data.
5. Data in lib/System classes must use only simple C++ intrinsic types.
6. Errors are handled by returning "true" and setting an optional std::string
7. Library must not throw any exceptions, period.
8. Interface functions must not have throw() specifications.
9. No duplicate function impementations are permitted within an operating
system class.
To accomplish these requirements, the library has numerous design criteria that
must be satisfied. Here's a high level summary of the library's design criteria:
1. No unused functionality (only what LLVM needs)
2. High-Level Interfaces
3. Use Opaque Classes
4. Common Implementations
5. Multiple Implementations
6. Minimize Memory Allocation
7. No Virtual Methods