make dynamic linker work around MAP_FAILED mmap failure on nommu kernels

previously, loading of additional libraries beyond libc/ldso did not
work on nommu kernels, nor did loading programs via invocation of the
dynamic linker as a command.

diff --git a/src/ldso/dynlink.c b/src/ldso/dynlink.c
index 7e566933d6ad97b83daf25a12fafecc9d0629247..b77c6f6b9c8c1dcce7acea8d5bee7128f501ef6d 100644 (file)
--- a/src/ldso/dynlink.c
+++ b/src/ldso/dynlink.c
@@ -423,6 +423,28 @@ static void reclaim_gaps(struct dso *dso)
        }
 }
 
+static void *mmap_fixed(void *p, size_t n, int prot, int flags, int fd, off_t off)
+{
+       char *q = mmap(p, n, prot, flags, fd, off);
+       if (q != MAP_FAILED || errno != EINVAL) return q;
+       /* Fallbacks for MAP_FIXED failure on NOMMU kernels. */
+       if (flags & MAP_ANONYMOUS) {
+               memset(p, 0, n);
+               return p;
+       }
+       ssize_t r;
+       if (lseek(fd, off, SEEK_SET) < 0) return MAP_FAILED;
+       for (q=p; n; q+=r, off+=r, n-=r) {
+               r = read(fd, q, n);
+               if (r < 0 && errno != EINTR) return MAP_FAILED;
+               if (!r) {
+                       memset(q, 0, n);
+                       break;
+               }
+       }
+       return p;
+}
+
 static void *map_library(int fd, struct dso *dso)
 {
        Ehdr buf[(896+sizeof(Ehdr))/sizeof(Ehdr)];
@@ -524,13 +546,13 @@ static void *map_library(int fd, struct dso *dso)
                prot = (((ph->p_flags&PF_R) ? PROT_READ : 0) |
                        ((ph->p_flags&PF_W) ? PROT_WRITE: 0) |
                        ((ph->p_flags&PF_X) ? PROT_EXEC : 0));
-               if (mmap(base+this_min, this_max-this_min, prot, MAP_PRIVATE|MAP_FIXED, fd, off_start) == MAP_FAILED)
+               if (mmap_fixed(base+this_min, this_max-this_min, prot, MAP_PRIVATE|MAP_FIXED, fd, off_start) == MAP_FAILED)
                        goto error;
                if (ph->p_memsz > ph->p_filesz) {
                        size_t brk = (size_t)base+ph->p_vaddr+ph->p_filesz;
                        size_t pgbrk = brk+PAGE_SIZE-1 & -PAGE_SIZE;
                        memset((void *)brk, 0, pgbrk-brk & PAGE_SIZE-1);
-                       if (pgbrk-(size_t)base < this_max && mmap((void *)pgbrk, (size_t)base+this_max-pgbrk, prot, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) == MAP_FAILED)
+                       if (pgbrk-(size_t)base < this_max && mmap_fixed((void *)pgbrk, (size_t)base+this_max-pgbrk, prot, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) == MAP_FAILED)
                                goto error;
                }
        }