Fix logic of get_binary_load_address

The value of the of the pointer to program header returned by
gelf_getphdr is always the same, assuming the value of the last
parameter to gelf_getphdr stays the same.  What changes is what is
pointed to by that pointer.  So rather than storing the the program
header (to determine the lowest load address among several program
headers returned by gelf_getphdr) we need to store the load address
pointed to by the pointer to the program header.

Thanks to Matthias Männich for spotting this and discussing it at
https://sourceware.org/ml/libabigail/2019-q2/msg00064.html.

Testing this is a bit annoying as we'd need to consider a prelinked binary which has
split debuginfo.  I should probably add such a binary to the regression
test suite at some point.

	* src/abg-dwarf-reader.cc (get_binary_load_address): Consider the
	load address pointed to by the program header pointer returned by
	gelf_getphdr rather than the program header itself.

Signed-off-by: Dodji Seketeli <dodji@redhat.com>

diff --git a/src/abg-dwarf-reader.cc b/src/abg-dwarf-reader.cc
index cd39fc3..7661819 100644 (file)
--- a/src/abg-dwarf-reader.cc
+++ b/src/abg-dwarf-reader.cc
@@ -1116,24 +1116,32 @@ get_binary_load_address(Elf *elf_handle,
   GElf_Ehdr eh_mem;
   GElf_Ehdr *elf_header = gelf_getehdr(elf_handle, &eh_mem);
   size_t num_segments = elf_header->e_phnum;
-  GElf_Phdr *lowest_program_header = 0, *program_header = 0;
+  GElf_Phdr *program_header = 0;
+  GElf_Addr result;
+  bool found_loaded_segment = false;
   GElf_Phdr ph_mem;
 
   for (unsigned i = 0; i < num_segments; ++i)
     {
       program_header = gelf_getphdr(elf_handle, i, &ph_mem);
-      if (program_header->p_type == PT_LOAD
-         && (!lowest_program_header
-             || program_header->p_vaddr < lowest_program_header->p_vaddr))
-       lowest_program_header = program_header;
+      if (program_header && program_header->p_type == PT_LOAD)
+       {
+         if (!found_loaded_segment)
+           {
+             result = program_header->p_vaddr;
+             found_loaded_segment = true;
+           }
+
+         if (program_header->p_vaddr < result)
+           // The resulting load address we want is the lowest
+           // load address of all the loaded segments.
+           result = program_header->p_vaddr;
+       }
     }
 
-  if (lowest_program_header)
+  if (found_loaded_segment)
     {
-      // This program header represent the segment containing the
-      // first byte of this binary.  We want to return the address
-      // at which the segment is loaded in memory.
-      load_address = lowest_program_header->p_vaddr;
+      load_address = result;
       return true;
     }
   return false;
@@ -7703,12 +7711,12 @@ public:
       {
        Dwarf_Addr dwarf_elf_load_address = 0, elf_load_address = 0;
        ABG_ASSERT(get_binary_load_address(dwarf_elf_handle(),
-                                      dwarf_elf_load_address));
+                                          dwarf_elf_load_address));
        ABG_ASSERT(get_binary_load_address(elf_handle(),
-                                      elf_load_address));
+                                          elf_load_address));
        if (dwarf_is_splitted()
            && (dwarf_elf_load_address != elf_load_address))
-         // This means that in theory the DWARF an the executable are
+         // This means that in theory the DWARF and the executable are
          // not loaded at the same address.  And addr is meaningful
          // only in the context of the DWARF.
          //