421a8ed412
While testing a patch on Solaris, which does not support split-stack, I
ran across a bug in the handling of caller-saved registers for the
garbage collector. For non-split-stack systems, runtime_mcall is
responsible for saving all caller-saved registers on the stack so that
the GC stack scan will see them. It does this by calling
__builtin_unwind_init and setting the g's gcnextsp field to point to the
current stack. The garbage collector then scans the stack from gcnextsp
to the top of stack.
Unfortunately, the code was setting gcnextsp to point to runtime_mcall's
argument, which meant that even though runtime_mcall was careful to
store all caller-saved registers on the stack, the GC never saw them.
This is, of course, only a problem if a value lives only in a
caller-saved register, and not anywhere else on the stack or heap. And
it is only a problem if that caller-saved register manages to make it
all the way down to runtime_mcall without being saved by any function on
the way. This is moderately unlikely but it turns out that the recent
changes to keep values on the stack when compiling the runtime package
caused it to happen for the local variable `s` in `notifyListWait` in
runtime/sema.go. That function calls goparkunlock which is simple
enough to not require all registers, and itself calls runtime_mcall. So
it was possible for `s` to be released by the GC before the goroutine
returned from goparkunlock, which eventually caused a dangling pointer
to be passed to releaseSudog.
This is not a problem on split-stack systems, which use
__splitstack_get_context, which saves a stack pointer low enough on the
stack to scan the registers saved by runtime_mcall.
Reviewed-on: https://go-review.googlesource.com/31323
From-SVN: r241304
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| .. | ||
| config | ||
| go | ||
| runtime | ||
| testsuite | ||
| aclocal.m4 | ||
| config.h.in | ||
| configure | ||
| configure.ac | ||
| godeps.sh | ||
| LICENSE | ||
| Makefile.am | ||
| Makefile.in | ||
| match.sh | ||
| MERGE | ||
| merge.sh | ||
| mkrsysinfo.sh | ||
| mksysinfo.sh | ||
| mvifdiff.sh | ||
| PATENTS | ||
| README | ||
| README.gcc | ||
| sysinfo.c | ||
| VERSION | ||
See ../README. This is the runtime support library for the Go programming language. This library is intended for use with the Go frontend. This library should not be stripped when it is installed. Go code relies on being able to look up file/line information, which comes from the debugging info using the libbacktrace library. The library has only been tested on GNU/Linux using glibc, and on Solaris. It should not be difficult to port to other operating systems. Directories: go A copy of the Go library from http://golang.org/, with several changes for gccgo. runtime Runtime functions, written in C, which are called directly by the compiler or by the library. Contributing ============ To contribute patches to the files in this directory, please see http://golang.org/doc/gccgo_contribute.html . The master copy of these files is hosted at http://code.google.com/p/gofrontend . Changes to these files require signing a Google contributor license agreement. If you are the copyright holder, you will need to agree to the individual contributor license agreement at http://code.google.com/legal/individual-cla-v1.0.html. This agreement can be completed online. If your organization is the copyright holder, the organization will need to agree to the corporate contributor license agreement at http://code.google.com/legal/corporate-cla-v1.0.html. If the copyright holder for your code has already completed the agreement in connection with another Google open source project, it does not need to be completed again.