abd471378c
The spans array is allocated in runtime_mallocinit. On a 32-bit system the number of entries in the spans array is MaxArena32 / PageSize, which (2U << 30) / (1 << 12) == (1 << 19). So we are allocating an array that can hold 19 bits for an index that can hold 20 bits. According to the comment in the function, this is intentional: we only allocate enough spans (and bitmaps) for a 2G arena, because allocating more would probably be wasteful. But since the span index is simply the upper 20 bits of the memory address, this scheme only works if memory addresses are limited to the low 2G of memory. That would be OK if we were careful to enforce it, but we're not. What we are careful to enforce, in functions like runtime_MHeap_SysAlloc, is that we always return addresses between the heap's arena_start and arena_start + MaxArena32. We generally get away with it because we start allocating just after the program end, so we only run into trouble with programs that allocate a lot of memory, enough to get past address 0x80000000. This changes the code that computes a span index to subtract arena_start on 32-bit systems just as we currently do on 64-bit systems. From-SVN: r206501 |
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.. | ||
config | ||
go | ||
runtime | ||
testsuite | ||
aclocal.m4 | ||
config.h.in | ||
configure | ||
configure.ac | ||
godeps.sh | ||
LICENSE | ||
Makefile.am | ||
Makefile.in | ||
MERGE | ||
merge.sh | ||
mksysinfo.sh | ||
PATENTS | ||
README | ||
README.gcc |
See ../README. This is the runtime support library for the Go programming language. This library is intended for use with the Go frontend. The library has only been tested on GNU/Linux using glibc. It should not be difficult to port to other operating systems. The library has only been tested on x86/x86_64 systems. It should not be difficult to port to other architectures. Directories: go A copy of the Go library from http://golang.org/, with a few changes for gccgo. Notably, the reflection interface is different. runtime Runtime functions, written in C, which are called directly by the compiler or by the library. syscalls System call support. 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.