mirror of
https://github.com/RPCS3/llvm-mirror.git
synced 2025-02-01 05:01:59 +01:00
73a92659e5
Summary: The function `llvm::sys::commandLineFitsWithinSystemLimits` appears to be overestimating the system limits. This issue was discovered while attempting to enable response files in the Swift compiler. When the compiler submits its frontend jobs, those jobs are subjected to the system limits on command line length. `commandLineFitsWithinSystemLimits` is used to determine if the job's arguments need to be wrapped in a response file. There are some cases where the argument size for the job passes `commandLineFitsWithinSystemLimits`, but actually exceeds the real system limit, and the job fails. `clang` also uses this function to decide whether or not to wrap it's job arguments in response files. See: https://github.com/llvm-mirror/clang/blob/master/lib/Driver/Driver.cpp#L1341. Clang will also fail for response files who's size falls within a certain range. I wrote a script that should find a failure point for `clang++`. All that is needed to run it is Python 2.7, and a simple "hello world" program for `test.cc`. It should run on Linux and on macOS. The script is available here: https://gist.github.com/dabelknap/71bd083cd06b91c5b3cef6a7f4d3d427. When it hits a failure point, you should see a `clang: error: unable to execute command: posix_spawn failed: Argument list too long`. The proposed solution is to mirror the behavior of `xargs` in `commandLinefitsWithinSystemLimits`. `xargs` defaults to 128k for the command line length size (See: https://fossies.org/dox/findutils-4.6.0/buildcmd_8c_source.html#l00551). It adjusts this depending on the value of `ARG_MAX`. Reviewers: alexfh Reviewed By: alexfh Subscribers: llvm-commits Tags: #clang Patch by Austin Belknap! Differential Revision: https://reviews.llvm.org/D47795 llvm-svn: 334295
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