runtime: size arena to fit in virtual address space limit

For Brad.
Now FreeBSD/386 binaries run on nearlyfreespeech.net.

Fixes #2302.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/5700060

1 files changed, 28 insertions, 0 deletions

diff --git a/src/pkg/runtime/thread_linux.c b/src/pkg/runtime/thread_linux.c
index 005fb1df6a..d406a71240 100644
--- a/src/pkg/runtime/thread_linux.c
+++ b/src/pkg/runtime/thread_linux.c
@@ -221,3 +221,31 @@ runtime·sigpanic(void)
 	}
 	runtime·panicstring(runtime·sigtab[g->sig].name);
 }
+
+uintptr
+runtime·memlimit(void)
+{
+	Rlimit rl;
+	extern byte text[], end[];
+	uintptr used;
+	
+	if(runtime·getrlimit(RLIMIT_AS, &rl) != 0)
+		return 0;
+	if(rl.rlim_cur >= 0x7fffffff)
+		return 0;
+
+	// Estimate our VM footprint excluding the heap.
+	// Not an exact science: use size of binary plus
+	// some room for thread stacks.
+	used = end - text + (64<<20);
+	if(used >= rl.rlim_cur)
+		return 0;
+
+	// If there's not at least 16 MB left, we're probably
+	// not going to be able to do much.  Treat as no limit.
+	rl.rlim_cur -= used;
+	if(rl.rlim_cur < (16<<20))
+		return 0;
+
+	return rl.rlim_cur - used;
+}