Question

我想学习如何创建更高效的malloc，我找到了这个项目。我可以运行make来编译它：

$ make tstmalloc
make: `tstmalloc' is up to date.

但我该如何运行并测试呢？我阅读了自述文件，但不够详细。我想编译所有程序，测试所有程序并了解程序的功能。但是，如果我只是运行，那么它会以我不理解的方式抱怨：

$ make
gcc  -g -Wall -ansi -DSTRATEGY=2   -c -o malloc.o malloc.c
malloc.c: In function ‘morecore’:
malloc.c:77:3: warning: implicit declaration of function ‘getpagesize’ [-Wimplicit-function-declaration]
   noPages = ((nu*sizeof(Header))-1)/getpagesize() + 1;
   ^
malloc.c:78:84: error: ‘MAP_ANONYMOUS’ undeclared (first use in this function)
   cp = mmap(__endHeap, noPages*getpagesize(), PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
                                                                                    ^
malloc.c:78:84: note: each undeclared identifier is reported only once for each function it appears in
malloc.c:85:5: warning: implicit declaration of function ‘perror’ [-Wimplicit-function-declaration]
     perror("failed to get more memory");
     ^
make: *** [malloc.o] Error 1

如果我尝试单独编译程序，我会收到另一个错误消息，我不明白：

$ gcc malloc.c 
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 0 has invalid symbol index 11

我malloc.c的内容是：

#include "brk.h"
#include <unistd.h>
#include <string.h> 
#include <errno.h> 
#include <sys/mman.h>

#define NALLOC 1024                                     /* minimum #units to request */

typedef long Align;                                     /* for alignment to long boundary */

union header {                                          /* block header */
  struct {
    union header *ptr;                                  /* next block if on free list */
    unsigned size;                                      /* size of this block  - what unit? */ 
  } s;
  Align x;                                              /* force alignment of blocks */
};

typedef union header Header;

static Header base;                                     /* empty list to get started */
static Header *freep = NULL;                            /* start of free list */

/* free: put block ap in the free list */

void free(void * ap)
{
  Header *bp, *p;

  if(ap == NULL) return;                                /* Nothing to do */

  bp = (Header *) ap - 1;                               /* point to block header */
  for(p = freep; !(bp > p && bp < p->s.ptr); p = p->s.ptr)
    if(p >= p->s.ptr && (bp > p || bp < p->s.ptr))
      break;                                            /* freed block at atrt or end of arena */

  if(bp + bp->s.size == p->s.ptr) {                     /* join to upper nb */
    bp->s.size += p->s.ptr->s.size;
    bp->s.ptr = p->s.ptr->s.ptr;
  }
  else
    bp->s.ptr = p->s.ptr;
  if(p + p->s.size == bp) {                             /* join to lower nbr */
    p->s.size += bp->s.size;
    p->s.ptr = bp->s.ptr;
  } else
    p->s.ptr = bp;
  freep = p;
}

/* morecore: ask system for more memory */

#ifdef MMAP

static void * __endHeap = 0;

void * endHeap(void)
{
  if(__endHeap == 0) __endHeap = sbrk(0);
  return __endHeap;
}
#endif


static Header *morecore(unsigned nu)
{
  void *cp;
  Header *up;
#ifdef MMAP
  unsigned noPages;
  if(__endHeap == 0) __endHeap = sbrk(0);
#endif

  if(nu < NALLOC)
    nu = NALLOC;
#ifdef MMAP
  noPages = ((nu*sizeof(Header))-1)/getpagesize() + 1;
  cp = mmap(__endHeap, noPages*getpagesize(), PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
  nu = (noPages*getpagesize())/sizeof(Header);
  __endHeap += noPages*getpagesize();
#else
  cp = sbrk(nu*sizeof(Header));
#endif
  if(cp == (void *) -1){                                 /* no space at all */
    perror("failed to get more memory");
    return NULL;
  }
  up = (Header *) cp;
  up->s.size = nu;
  free((void *)(up+1));
  return freep;
}

void * malloc(size_t nbytes)
{
  Header *p, *prevp;
  Header * morecore(unsigned);
  unsigned nunits;

  if(nbytes == 0) return NULL;

  nunits = (nbytes+sizeof(Header)-1)/sizeof(Header) +1;

  if((prevp = freep) == NULL) {
    base.s.ptr = freep = prevp = &base;
    base.s.size = 0;
  }
  for(p= prevp->s.ptr;  ; prevp = p, p = p->s.ptr) {
    if(p->s.size >= nunits) {                           /* big enough */
      if (p->s.size == nunits)                          /* exactly */
    prevp->s.ptr = p->s.ptr;
      else {                                            /* allocate tail end */
    p->s.size -= nunits;
    p += p->s.size;
    p->s.size = nunits;
      }
      freep = prevp;
      return (void *)(p+1);
    }
    if(p == freep)                                      /* wrapped around free list */
      if((p = morecore(nunits)) == NULL)
    return NULL;                                    /* none left */
  }
}

Answer 1

66 static Header *morecore(
67     unsigned nu) /* the amount of memory to ask for (in Header-sized units) */
68 {
69     char *cp;
70     Header *up;
71     if (nu < NALLOC)
72         nu = NALLOC;
73     cp = sbrk(nu * sizeof(Header));
74     if (cp == (char *) -1) /* no space at all */
75         return NULL;
76     up = (Header *) cp;
77     up->s.size = nu;
78     free((void *)(up+1));
79     return freep;
80 }

您的错误是指malloc.c的第77行为no_pages = ...，但GitHub上的当前代码不是<div ng-app="routerApp" ng-controller="ctrl"> <div class="form-group" ng-style="{'background-color': color}"> <label>Background color for views</label> <input type="color" name="background_color" id="background_color" ng-model="color" class="form-control" /> </div> </div>。所以在malloc.c中发布你的内容，或者从GitHub获取最新的代码。

我该如何编译和运行这个项目？

1 个答案: