Non-SFI Mode: Add nonsfi_loader and plumbing to test it

src/nonsfi/loader/elf_loader.c

+/*
+ * Copyright (c) 2014 The Native Client 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 <elf.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <link.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+#include "native_client/src/nonsfi/irt/irt_interfaces.h"
+#include "native_client/src/shared/platform/nacl_log.h"
+#include "native_client/src/trusted/service_runtime/nacl_config.h"
+
+
+#define PAGE_SIZE 0x1000

[bradn, 2014/05/02 17:39:11]

There's an odd irony in baking this in given it wouldn't have applied to nacl.
:-)

[Mark Seaborn, 2014/05/02 18:18:50]

Since you mention it, I've added a comment.

+#define PAGE_MASK (PAGE_SIZE - 1)
+#define MAX_PHNUM 128
+
+static uintptr_t PageSizeRoundDown(uintptr_t addr) {
+  return addr & ~PAGE_MASK;
+}
+
+static uintptr_t PageSizeRoundUp(uintptr_t addr) {
+  return PageSizeRoundDown(addr + PAGE_SIZE - 1);
+}
+
+static int ElfFlagsToMmapFlags(int pflags) {
+  return ((pflags & PF_X) != 0 ? PROT_EXEC : 0) |
+         ((pflags & PF_R) != 0 ? PROT_READ : 0) |
+         ((pflags & PF_W) != 0 ? PROT_WRITE : 0);
+}
+
+static void CheckElfHeaders(ElfW(Ehdr) *ehdr) {
+  if (memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0) {
+    NaClLog(LOG_FATAL, "Not an ELF file: no ELF header\n");
+  }
+  if (ehdr->e_ident[EI_CLASS] != ELFCLASS32) {
+    NaClLog(LOG_FATAL, "Unexpected ELF class: not ELFCLASS32\n");
+  }
+  if (ehdr->e_ident[EI_DATA] != ELFDATA2LSB) {
+    NaClLog(LOG_FATAL, "Not a little-endian ELF file\n");
+  }
+  if (ehdr->e_type != ET_DYN) {
+    NaClLog(LOG_FATAL, "Not a relocatable ELF object (not ET_DYN)\n");
+  }
+  if (ehdr->e_machine != NACL_ELF_E_MACHINE) {
+    NaClLog(LOG_FATAL, "Unexpected ELF e_machine field\n");
+  }
+  if (ehdr->e_version != EV_CURRENT) {
+    NaClLog(LOG_FATAL, "Unexpected ELF e_version field\n");
+  }
+  if (ehdr->e_ehsize != sizeof(*ehdr)) {
+    NaClLog(LOG_FATAL, "Unexpected ELF e_ehsize field\n");
+  }
+  if (ehdr->e_phentsize != sizeof(ElfW(Phdr))) {
+    NaClLog(LOG_FATAL, "Unexpected ELF e_phentsize field\n");
+  }
+}
+
+static uintptr_t LoadElfFile(const char *filename) {
+  int fd = open(filename, O_RDONLY);
+  if (fd < 0) {
+    NaClLog(LOG_FATAL, "Failed to open %s: %s\n", filename, strerror(errno));
+  }
+
+  /* Read ELF file headers. */
+  ElfW(Ehdr) ehdr;
+  ssize_t bytes_read = pread(fd, &ehdr, sizeof(ehdr), 0);
+  if (bytes_read != sizeof(ehdr)) {
+    NaClLog(LOG_FATAL, "Failed to read ELF file headers\n");
+  }
+  CheckElfHeaders(&ehdr);
+
+  /* Read ELF program headers. */
+  if (ehdr.e_phnum > MAX_PHNUM) {
+    NaClLog(LOG_FATAL, "ELF file has too many program headers\n");
+  }
+  ElfW(Phdr) phdr[MAX_PHNUM];
+  ssize_t phdrs_size = sizeof(phdr[0]) * ehdr.e_phnum;
+  bytes_read = pread(fd, phdr, phdrs_size, ehdr.e_phoff);
+  if (bytes_read != phdrs_size) {
+    NaClLog(LOG_FATAL, "Failed to read ELF program headers\n");
+  }
+
+  /* Find the first PT_LOAD segment. */
+  size_t i = 0;

[bradn, 2014/05/02 17:39:11]

Given you're using i beyond the loop, maybe a more descriptive variable (or put
it in one later)?

[Mark Seaborn, 2014/05/02 18:18:50]

Done.

+  while (i < ehdr.e_phnum && phdr[i].p_type != PT_LOAD)
+    ++i;
+  if (i == ehdr.e_phnum) {
+    NaClLog(LOG_FATAL, "ELF file has no PT_LOAD header\n");
+  }
+
+  /*
+   * ELF requires that PT_LOAD segments be in ascending order of p_vaddr.
+   * Find the last one to calculate the whole address span of the image.
+   */
+  ElfW(Phdr) *first_load = &phdr[i];
+  ElfW(Phdr) *last_load = &phdr[ehdr.e_phnum - 1];
+  while (last_load > first_load && last_load->p_type != PT_LOAD)
+    --last_load;
+
+  if (first_load->p_vaddr != 0) {
+    NaClLog(LOG_FATAL, "First PT_LOAD segment's load address is not 0\n");
+  }
+  size_t span = last_load->p_vaddr + last_load->p_memsz;
+
+  /* Reserve address space. */
+  void *mapping = mmap(NULL, span, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE,
+                       -1, 0);
+  if (mapping == MAP_FAILED) {
+    NaClLog(LOG_FATAL, "Failed to reserve address space for executable\n");
+  }
+  uintptr_t load_bias = (uintptr_t) mapping;
+
+  uintptr_t prev_segment_end = 0;
+  ElfW(Phdr) *ph;
+  for (ph = first_load; ph <= last_load; ++ph) {
+    if (ph->p_type == PT_LOAD) {

[bradn, 2014/05/02 17:39:11]

might be more readable with continue, to avoid the indent.

[Mark Seaborn, 2014/05/02 18:18:50]

Done.

+      int prot = ElfFlagsToMmapFlags(ph->p_flags);
+      uintptr_t segment_start = PageSizeRoundDown(ph->p_vaddr);
+      uintptr_t segment_end = PageSizeRoundUp(ph->p_vaddr + ph->p_memsz);
+      if (segment_start < prev_segment_end) {
+        NaClLog(LOG_FATAL, "PT_LOAD segments overlap or are not sorted\n");
+      }
+      prev_segment_end = segment_end;
+      void *segment_addr = (void *) (load_bias + segment_start);
+      void *map_result = mmap((void *) segment_addr,
+                              segment_end - segment_start,
+                              prot, MAP_PRIVATE | MAP_FIXED, fd,
+                              PageSizeRoundDown(ph->p_offset));
+      if (map_result != segment_addr) {
+        NaClLog(LOG_FATAL, "Failed to map ELF segment\n");
+      }
+
+      /* Handle the BSS. */
+      if (ph->p_memsz < ph->p_filesz) {
+        NaClLog(LOG_FATAL, "Bad ELF segment: p_memsz < p_filesz\n");
+      }
+      if (ph->p_memsz > ph->p_filesz) {
+        if ((ph->p_flags & PF_W) == 0) {
+          NaClLog(LOG_FATAL,
+                  "Bad ELF segment: non-writable segment with BSS\n");
+        }
+
+        uintptr_t bss_start = ph->p_vaddr + ph->p_filesz;
+        uintptr_t bss_map_start = PageSizeRoundUp(bss_start);
+        /*
+         * Zero the BSS to the end of the page.
+         *
+         * Zeroing beyond p_memsz might be more than is necessary for
+         * Non-SFI NaCl.  On Linux, programs such as ld.so use the rest of
+         * the page, after p_memsz, as part of the brk() heap and assume
+         * that it has been zeroed.  Non-SFI NaCl does not provide a brk()
+         * heap, though.  However, zeroing to the end of the page is simple
+         * enough, and it's consistent with the case in additional pages
+         * must be mapped, which will all be fully zeroed.
+         */
+        memset((void *) (load_bias + bss_start), 0, bss_map_start - bss_start);
+
+        if (bss_map_start < segment_end) {
+          void *map_addr = (void *) (load_bias + bss_map_start);
+          map_result = mmap(map_addr, segment_end - bss_map_start,
+                            prot, MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED,
+                            -1, 0);
+          if (map_result != map_addr) {
+            NaClLog(LOG_FATAL, "Failed to map BSS for ELF segment\n");
+          }
+        }
+      }
+    }
+  }
+
+  if (close(fd) != 0) {
+    NaClLog(LOG_FATAL, "close() failed\n");
+  }
+
+  return load_bias + ehdr.e_entry;

[bradn, 2014/05/02 17:39:11]

Check it's in one of the sections?

[Mark Seaborn, 2014/05/02 18:18:50]

OK.  I've even checked that it's in an executable segment's pre-page-alignment
range.

+}
+
+int main(int argc, char **argv, char **environ) {
+  if (argc < 2) {
+    fprintf(stderr, "Usage: %s <executable> <args...>\n", argv[0]);
+    return 1;
+  }
+  const char *nexe_filename = argv[1];
+  uintptr_t entry = LoadElfFile(nexe_filename);
+  return nacl_irt_nonsfi_entry(argc, argv, environ, (nacl_entry_func_t) entry);
+}