[glibc] elf: Use nocancel pread64() instead of lseek()+read()

[glibc] elf: Use nocancel pread64() instead of lseek()+read()

[Carlos O'Donell]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=95c1056962a3f2297c94ce47f0eaf0c5b6563231

commit 95c1056962a3f2297c94ce47f0eaf0c5b6563231
Author: Leandro Pereira <leandro.pereira@microsoft.com>
Date:   Wed Oct 2 12:48:17 2019 -0400

    elf: Use nocancel pread64() instead of lseek()+read()
    
    Transforms this, when linking in a shared object:
    
      openat(AT_FDCWD, "/lib64/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
      read(3, "\177ELF\2\1\1\3"..., 832) = 832
      lseek(3, 792, SEEK_SET)           = 792
      read(3, "\4\0\0\0\24\0\0\0"..., 68) = 68
      fstat(3, {st_mode=S_IFREG|0755, st_size=6699224, ...}) = 0
      lseek(3, 792, SEEK_SET)           = 792
      read(3, "\4\0\0\0\24\0\0\0"..., 68) = 68
      lseek(3, 864, SEEK_SET)           = 864
      read(3, "\4\0\0\0\20\0\0\0"..., 32) = 32
    
    Into this:
    
      openat(AT_FDCWD, "/lib64/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
      read(3, "\177ELF\2\1\1\3"..., 832) = 832
      pread(3, "\4\0\0\0\24\0\0\0"..., 68, 792) = 68
      fstat(3, {st_mode=S_IFREG|0755, st_size=6699224, ...}) = 0
      pread(3, "\4\0\0\0\24\0\0\0"..., 68, 792) = 68
      pread(3, "\4\0\0\0\20\0\0\0"..., 32, 864) = 32
    
    Reviewed-by: Carlos O'Donell <carlos@redhat.com>

Diff:
---
 elf/dl-load.c         | 13 ++++++-------
 sysdeps/x86/dl-prop.h |  3 +--
 2 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/elf/dl-load.c b/elf/dl-load.c
index 1ed7a7b..c1bc8c2 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -1015,8 +1015,8 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
   else
     {
       phdr = alloca (maplength);
-      __lseek (fd, header->e_phoff, SEEK_SET);
-      if ((size_t) __read_nocancel (fd, (void *) phdr, maplength) != maplength)
+      if ((size_t) __pread64_nocancel (fd, (void *) phdr, maplength,
+				       header->e_phoff) != maplength)
 	{
 	  errstring = N_("cannot read file data");
 	  goto call_lose_errno;
@@ -1664,9 +1664,8 @@ open_verify (const char *name, int fd,
       else
 	{
 	  phdr = alloca (maplength);
-	  __lseek (fd, ehdr->e_phoff, SEEK_SET);
-	  if ((size_t) __read_nocancel (fd, (void *) phdr, maplength)
-	      != maplength)
+	  if ((size_t) __pread64_nocancel (fd, (void *) phdr, maplength,
+					   ehdr->e_phoff) != maplength)
 	    {
 	    read_error:
 	      errval = errno;
@@ -1704,8 +1703,8 @@ open_verify (const char *name, int fd,
 
 		    abi_note = abi_note_malloced;
 		  }
-		__lseek (fd, ph->p_offset, SEEK_SET);
-		if (__read_nocancel (fd, (void *) abi_note, size) != size)
+		if (__pread64_nocancel (fd, (void *) abi_note, size,
+					ph->p_offset) != size)
 		  {
 		    free (abi_note_malloced);
 		    goto read_error;
diff --git a/sysdeps/x86/dl-prop.h b/sysdeps/x86/dl-prop.h
index a99eec1..fa5bd98 100644
--- a/sysdeps/x86/dl-prop.h
+++ b/sysdeps/x86/dl-prop.h
@@ -167,8 +167,7 @@ _dl_process_pt_note (struct link_map *l, const ElfW(Phdr) *ph,
 	  note_malloced = malloc (size);
 	  note = note_malloced;
 	}
-      __lseek (fd, ph->p_offset, SEEK_SET);
-      if (__read_nocancel (fd, (void *) note, size) != size)
+      if (__pread64_nocancel (fd, (void *) note, size, ph->p_offset) != size)
 	{
 	  if (note_malloced)
 	    free (note_malloced);