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runtime: update comment for the "extern register" variables g and m.

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R=rsc, minux.ma, ality
CC=dave, golang-dev
https://golang.org/cl/6620050
This commit is contained in:
Nigel Tao 2012-10-19 11:02:32 +11:00
parent 5abf4bdc27
commit 90ad6a2d11
1 changed files with 10 additions and 11 deletions
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21
src/pkg/runtime/runtime.h
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@ -82,19 +82,18 @@ typedef struct ParFor ParFor;
typedef struct ParForThread ParForThread;
/*
* per-cpu declaration.
* Per-CPU declaration.
*
* "extern register" is a special storage class implemented by 6c, 8c, etc.
* on machines with lots of registers, it allocates a register that will not be
* used in generated code. on the x86, it allocates a slot indexed by a
* segment register.
* On the ARM, it is an actual register; elsewhere it is a slot in thread-
* local storage indexed by a segment register. See zasmhdr in
* src/cmd/dist/buildruntime.c for details, and be aware that the linker may
* make further OS-specific changes to the compiler's output. For example,
* 6l/linux rewrites 0(GS) as -16(FS).
*
* amd64: allocated downwards from R15
* x86: allocated upwards from 0(GS)
* arm: allocated downwards from R10
*
* every C file linked into a Go program must include runtime.h
* so that the C compiler knows to avoid other uses of these registers.
* the Go compilers know to avoid them.
* Every C file linked into a Go program must include runtime.h so that the
* C compiler (6c, 8c, etc.) knows to avoid other uses of these dedicated
* registers. The Go compiler (6g, 8g, etc.) knows to avoid them.
*/
extern register G* g;
extern register M* m;