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3ea50a69d7
The llvm::sys::AddSignalHandler function (as well as related routines) in lib/Support/Unix/Signals.inc currently registers a signal handler routine via "sigaction". When this handler is called due to a SIGSEGV, SIGILL or similar signal, it will show a stack backtrace, deactivate the handler, and then simply return to the operating system. The intent is that the OS will now retry execution at the same location as before, which ought to again trigger the same error condition and cause the same signal to be delivered again. Since the hander is now deactivated, the OS will take its default action (usually, terminate the program and possibly create a core dump). However, this method doesn't work reliably on System Z: With certain signals (namely SIGILL, SIGFPE, and SIGTRAP), the program counter stored by the kernel on the signal stack frame (which is the location where execution will resume) is not the instruction that triggered the fault, but then instruction *after it*. When the LLVM signal handler simply returns to the kernel, execution will then resume at *that* address, which will not trigger the problem again, but simply go on and execute potentially unrelated code leading to random errors afterwards. To fix this, the patch simply goes and re-raises the signal in question directly from the handler instead of returning from it. This is done only on System Z and only for those signals that have this particular problem. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181010 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