Avoid ubsan complaint in BFD

I built gdb with ubsan and ran the test suite.

One complaint was due to bfd_get_elf_phdrs passing NULL to memcpy.
This patch avoids the complaint.

bfd/ChangeLog
2018-07-23  Tom Tromey  <tom@tromey.com>

	* elf.c (bfd_get_elf_phdrs): Don't call memcpy with size 0.

2 files changed, 7 insertions, 2 deletions

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index 5b79a25..19fd9df 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,7 @@
+2018-07-23  Tom Tromey  <tom@tromey.com>
+
+	* elf.c (bfd_get_elf_phdrs): Don't call memcpy with size 0.
+
 2018-07-21  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* elf32-arm.c (elf32_arm_final_link_relocate) <R_ARM_GOT32>: Small
diff --git a/bfd/elf.c b/bfd/elf.c
index 874629d..f721827 100644
--- a/bfd/elf.c
+++ b/bfd/elf.c
@@ -11629,8 +11629,9 @@ bfd_get_elf_phdrs (bfd *abfd, void *phdrs)
     }
 
   num_phdrs = elf_elfheader (abfd)->e_phnum;
-  memcpy (phdrs, elf_tdata (abfd)->phdr,
-	  num_phdrs * sizeof (Elf_Internal_Phdr));
+  if (num_phdrs != 0)
+    memcpy (phdrs, elf_tdata (abfd)->phdr,
+	    num_phdrs * sizeof (Elf_Internal_Phdr));
 
   return num_phdrs;
 }