all: remove 'extern register M *m' from runtime
The runtime has historically held two dedicated values g (current goroutine)
and m (current thread) in 'extern register' slots (TLS on x86, real registers
backed by TLS on ARM).
This CL removes the extern register m; code now uses g->m.
On ARM, this frees up the register that formerly held m (R9).
This is important for NaCl, because NaCl ARM code cannot use R9 at all.
The Go 1 macrobenchmarks (those with per-op times >= 10 µs) are unaffected:
BenchmarkBinaryTree17 5491374955 5471024381 -0.37%
BenchmarkFannkuch11 4357101311 4275174828 -1.88%
BenchmarkGobDecode 11029957 11364184 +3.03%
BenchmarkGobEncode 6852205 6784822 -0.98%
BenchmarkGzip 650795967 650152275 -0.10%
BenchmarkGunzip 140962363 141041670 +0.06%
BenchmarkHTTPClientServer 71581 73081 +2.10%
BenchmarkJSONEncode 31928079 31913356 -0.05%
BenchmarkJSONDecode 117470065 113689916 -3.22%
BenchmarkMandelbrot200 6008923 5998712 -0.17%
BenchmarkGoParse 6310917 6327487 +0.26%
BenchmarkRegexpMatchMedium_1K 114568 114763 +0.17%
BenchmarkRegexpMatchHard_1K 168977 169244 +0.16%
BenchmarkRevcomp 935294971 914060918 -2.27%
BenchmarkTemplate 145917123 148186096 +1.55%
Minux previous reported larger variations, but these were caused by
run-to-run noise, not repeatable slowdowns.
Actual code changes by Minux.
I only did the docs and the benchmarking.
LGTM=dvyukov, iant, minux
R=minux, josharian, iant, dave, bradfitz, dvyukov
CC=golang-codereviews
https://golang.org/cl/109050043
diff --git a/src/pkg/runtime/sys_netbsd_arm.s b/src/pkg/runtime/sys_netbsd_arm.s
index b2eb74e..acf01cf 100644
--- a/src/pkg/runtime/sys_netbsd_arm.s
+++ b/src/pkg/runtime/sys_netbsd_arm.s
@@ -80,7 +80,7 @@
RET
TEXT runtime·lwp_tramp(SB),NOSPLIT,$0
- MOVW R0, m
+ MOVW R0, g_m(R1)
MOVW R1, g
BL runtime·emptyfunc(SB) // fault if stack check is wrong
@@ -200,14 +200,14 @@
TEXT runtime·sigtramp(SB),NOSPLIT,$24
// this might be called in external code context,
- // where g and m are not set.
- // first save R0, because runtime·load_gm will clobber it
+ // where g is not set.
+ // first save R0, because runtime·load_g will clobber it
MOVW R0, 4(R13) // signum
MOVB runtime·iscgo(SB), R0
CMP $0, R0
- BL.NE runtime·load_gm(SB)
+ BL.NE runtime·load_g(SB)
- CMP $0, m
+ CMP $0, g
BNE 4(PC)
// signal number is already prepared in 4(R13)
MOVW $runtime·badsignal(SB), R11
@@ -219,7 +219,8 @@
MOVW g, 20(R13)
// g = m->signal
- MOVW m_gsignal(m), g
+ MOVW g_m(g), R8
+ MOVW m_gsignal(R8), g
// R0 is already saved
MOVW R1, 8(R13) // info
