root/src/pkg/runtime/mem_linux.c

DEFINITIONS

1. addrspace_free
2. mmap_fixed
3. runtime·SysAlloc
4. runtime·SysUnused
5. runtime·SysUsed
6. runtime·SysFree
7. runtime·SysFault
8. runtime·SysReserve
9. runtime·SysMap

// Copyright 2010 The Go Authors.  All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

#include "runtime.h"
#include "arch_GOARCH.h"
#include "defs_GOOS_GOARCH.h"
#include "os_GOOS.h"
#include "malloc.h"

enum
{
        _PAGE_SIZE = 4096,
        EACCES = 13,
};

static int32
addrspace_free(void *v, uintptr n)
{
        int32 errval;
        uintptr chunk;
        uintptr off;
        
        // NOTE: vec must be just 1 byte long here.
        // Mincore returns ENOMEM if any of the pages are unmapped,
        // but we want to know that all of the pages are unmapped.
        // To make these the same, we can only ask about one page
        // at a time. See golang.org/issue/7476.
        static byte vec[1];

        for(off = 0; off < n; off += chunk) {
                chunk = _PAGE_SIZE * sizeof vec;
                if(chunk > (n - off))
                        chunk = n - off;
                errval = runtime·mincore((int8*)v + off, chunk, vec);
                // ENOMEM means unmapped, which is what we want.
                // Anything else we assume means the pages are mapped.
                if (errval != -ENOMEM)
                        return 0;
        }
        return 1;
}

static void *
mmap_fixed(byte *v, uintptr n, int32 prot, int32 flags, int32 fd, uint32 offset)
{
        void *p;

        p = runtime·mmap(v, n, prot, flags, fd, offset);
        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, flags|MAP_FIXED, fd, offset);
        }
        return p;
}

void*
runtime·SysAlloc(uintptr n, uint64 *stat)
{
        void *p;

        p = runtime·mmap(nil, n, PROT_READ|PROT_WRITE, MAP_ANON|MAP_PRIVATE, -1, 0);
        if(p < (void*)4096) {
                if(p == (void*)EACCES) {
                        runtime·printf("runtime: mmap: access denied\n");
                        runtime·printf("if you're running SELinux, enable execmem for this process.\n");
                        runtime·exit(2);
                }
                if(p == (void*)EAGAIN) {
                        runtime·printf("runtime: mmap: too much locked memory (check 'ulimit -l').\n");
                        runtime·exit(2);
                }
                return nil;
        }
        runtime·xadd64(stat, n);
        return p;
}

void
runtime·SysUnused(void *v, uintptr n)
{
        runtime·madvise(v, n, MADV_DONTNEED);
}

void
runtime·SysUsed(void *v, uintptr n)
{
        USED(v);
        USED(n);
}

void
runtime·SysFree(void *v, uintptr n, uint64 *stat)
{
        runtime·xadd64(stat, -(uint64)n);
        runtime·munmap(v, n);
}

void
runtime·SysFault(void *v, uintptr n)
{
        runtime·mmap(v, n, PROT_NONE, MAP_ANON|MAP_PRIVATE|MAP_FIXED, -1, 0);
}

void*
runtime·SysReserve(void *v, uintptr n, bool *reserved)
{
        void *p;

        // On 64-bit, people with ulimit -v set complain if we reserve too
        // much address space.  Instead, assume that the reservation is okay
        // if we can reserve at least 64K and check the assumption in SysMap.
        // Only user-mode Linux (UML) rejects these requests.
        if(sizeof(void*) == 8 && n > 1LL<<32) {
                p = mmap_fixed(v, 64<<10, PROT_NONE, MAP_ANON|MAP_PRIVATE, -1, 0);
                if (p != v) {
                        if(p >= (void*)4096)
                                runtime·munmap(p, 64<<10);
                        return nil;
                }
                runtime·munmap(p, 64<<10);
                *reserved = false;
                return v;
        }

        p = runtime·mmap(v, n, PROT_NONE, MAP_ANON|MAP_PRIVATE, -1, 0);
        if((uintptr)p < 4096)
                return nil;
        *reserved = true;
        return p;
}

void
runtime·SysMap(void *v, uintptr n, bool reserved, uint64 *stat)
{
        void *p;
        
        runtime·xadd64(stat, n);

        // On 64-bit, we don't actually have v reserved, so tread carefully.
        if(!reserved) {
                p = mmap_fixed(v, n, PROT_READ|PROT_WRITE, MAP_ANON|MAP_PRIVATE, -1, 0);
                if(p == (void*)ENOMEM)
                        runtime·throw("runtime: out of memory");
                if(p != v) {
                        runtime·printf("runtime: address space conflict: map(%p) = %p\n", v, p);
                        runtime·throw("runtime: address space conflict");
                }
                return;
        }

        p = runtime·mmap(v, n, PROT_READ|PROT_WRITE, MAP_ANON|MAP_FIXED|MAP_PRIVATE, -1, 0);
        if(p == (void*)ENOMEM)
                runtime·throw("runtime: out of memory");
        if(p != v)
                runtime·throw("runtime: cannot map pages in arena address space");
}