From 65b036c38107ef805edc7734b705157a8d9d43bd Mon Sep 17 00:00:00 2001 From: Gustavo Niemeyer Date: Fri, 24 Jun 2011 00:29:59 -0300 Subject: [PATCH] runtime: don't use twice the memory with grsec-like kernels grsec needs the FIXED flag to be provided to mmap, which works now. That said, when the allocation fails to be made in the specific address, we're still given back a writable page. This change will unmap that page to avoid using twice the amount of memory needed. It'd also be pretty easy to avoid the extra system calls once we detected that the flag is needed, but I'm not sure if that edge case is worth the effort. R=golang-dev, rsc CC=golang-dev https://golang.org/cl/4634086 --- src/pkg/runtime/linux/mem.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/src/pkg/runtime/linux/mem.c b/src/pkg/runtime/linux/mem.c index 38ca7e4a0f9..ad0fac6d3f4 100644 --- a/src/pkg/runtime/linux/mem.c +++ b/src/pkg/runtime/linux/mem.c @@ -91,6 +91,9 @@ runtime·SysMap(void *v, uintptr n) if(p != v && addrspace_free(v, n)) { // On some systems, mmap ignores v without // MAP_FIXED, so retry if the address space is free. + if(p > (void*)4096) { + runtime·munmap(p, n); + } p = runtime·mmap(v, n, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_ANON|MAP_FIXED|MAP_PRIVATE, -1, 0); } if(p == (void*)ENOMEM)