Re: [PATCH] readelf: Show set_loc argument as hexadecimal

[Mark Wielaard <mark at klomp dot org>]

On Wed, Jan 20, 2016 at 03:14:16PM -0800, Roland McGrath wrote:
> > Other addresses in this code are printed with ("%#" PRIx64).
> > (AFAIK '#' here will always give "0x", but lets keep it consistent).
> 
> %#x prints "0" for zero (not "0x0").  Indeed it is the right thing to use here.
> 
> > It's also curious that nothing is done with op1 after printing it.
> > Shouldn't this set pc, at least?
> 
> I think it should, but that is unrelated to this change.
> Arguably, it should be:
> 
> 	  get_uleb128 (op1, readp, endp);
> 	  op1 *= code_align;
> 	  printf ("     set_loc %#" PRIx64 " to %#" PRIx64 "\n",
> 		  op1, pc = vma_base + op1);
> 
> so that it displays the literal value (like the other cases do) as well as
> the final value (which in this case is just with VMA_BASE added in).

I agree with using %# for printing the address and setting the pc using
vma_base and op1. But the argument of a DW_CFA_set_loc is an address, not
a uleb128 and it should not be adjusted by code_align, which is only used
for CFA_advance operations as far as I understand it. To read an address
we need to know the FDE address encoding and use read_encoded (which
isn't defined till a bit later, so we need to move it up).

So I believe the full change should be:

diff --git a/src/readelf.c b/src/readelf.c
index 0db192e..a25e4ac 100644
--- a/src/readelf.c
+++ b/src/readelf.c
@@ -5044,11 +5044,68 @@ register_info (Ebl *ebl, unsigned int regno, const Ebl_Register_Location *loc,
   return set;
 }
 
+static const unsigned char *
+read_encoded (unsigned int encoding, const unsigned char *readp,
+	      const unsigned char *const endp, uint64_t *res, Dwarf *dbg)
+{
+  if ((encoding & 0xf) == DW_EH_PE_absptr)
+    encoding = gelf_getclass (dbg->elf) == ELFCLASS32
+      ? DW_EH_PE_udata4 : DW_EH_PE_udata8;
+
+  switch (encoding & 0xf)
+    {
+    case DW_EH_PE_uleb128:
+      get_uleb128 (*res, readp, endp);
+      break;
+    case DW_EH_PE_sleb128:
+      get_sleb128 (*res, readp, endp);
+      break;
+    case DW_EH_PE_udata2:
+      if (readp + 2 > endp)
+	goto invalid;
+      *res = read_2ubyte_unaligned_inc (dbg, readp);
+      break;
+    case DW_EH_PE_udata4:
+      if (readp + 4 > endp)
+	goto invalid;
+      *res = read_4ubyte_unaligned_inc (dbg, readp);
+      break;
+    case DW_EH_PE_udata8:
+      if (readp + 8 > endp)
+	goto invalid;
+      *res = read_8ubyte_unaligned_inc (dbg, readp);
+      break;
+    case DW_EH_PE_sdata2:
+      if (readp + 2 > endp)
+	goto invalid;
+      *res = read_2sbyte_unaligned_inc (dbg, readp);
+      break;
+    case DW_EH_PE_sdata4:
+      if (readp + 4 > endp)
+	goto invalid;
+      *res = read_4sbyte_unaligned_inc (dbg, readp);
+      break;
+    case DW_EH_PE_sdata8:
+      if (readp + 8 > endp)
+	goto invalid;
+      *res = read_8sbyte_unaligned_inc (dbg, readp);
+      break;
+    default:
+    invalid:
+      error (1, 0,
+	     gettext ("invalid encoding"));
+    }
+
+  return readp;
+}
+
+
 static void
 print_cfa_program (const unsigned char *readp, const unsigned char *const endp,
 		   Dwarf_Word vma_base, unsigned int code_align,
 		   int data_align,
 		   unsigned int version, unsigned int ptr_size,
+		   unsigned int encoding,
 		   Dwfl_Module *dwflmod, Ebl *ebl, Dwarf *dbg)
 {
   char regnamebuf[REGNAMESZ];
@@ -5079,9 +5136,9 @@ print_cfa_program (const unsigned char *readp, const unsigned char *const endp,
 	  case DW_CFA_set_loc:
 	    if ((uint64_t) (endp - readp) < 1)
 	      goto invalid;
-	    get_uleb128 (op1, readp, endp);
-	    op1 += vma_base;
-	    printf ("     set_loc %" PRIu64 "\n", op1 * code_align);
+	    readp = read_encoded (encoding, readp, endp, &op1, dbg);
+	    printf ("     set_loc %#" PRIx64 " to %#" PRIx64 "\n",
+		    op1, pc = vma_base + op1);
 	    break;
 	  case DW_CFA_advance_loc1:
 	    if ((uint64_t) (endp - readp) < 1)
@@ -5421,62 +5478,6 @@ print_encoding_base (const char *pfx, unsigned int fde_encoding)
 }
 
 
-static const unsigned char *
-read_encoded (unsigned int encoding, const unsigned char *readp,
-	      const unsigned char *const endp, uint64_t *res, Dwarf *dbg)
-{
-  if ((encoding & 0xf) == DW_EH_PE_absptr)
-    encoding = gelf_getclass (dbg->elf) == ELFCLASS32
-      ? DW_EH_PE_udata4 : DW_EH_PE_udata8;
-
-  switch (encoding & 0xf)
-    {
-    case DW_EH_PE_uleb128:
-      get_uleb128 (*res, readp, endp);
-      break;
-    case DW_EH_PE_sleb128:
-      get_sleb128 (*res, readp, endp);
-      break;
-    case DW_EH_PE_udata2:
-      if (readp + 2 > endp)
-	goto invalid;
-      *res = read_2ubyte_unaligned_inc (dbg, readp);
-      break;
-    case DW_EH_PE_udata4:
-      if (readp + 4 > endp)
-	goto invalid;
-      *res = read_4ubyte_unaligned_inc (dbg, readp);
-      break;
-    case DW_EH_PE_udata8:
-      if (readp + 8 > endp)
-	goto invalid;
-      *res = read_8ubyte_unaligned_inc (dbg, readp);
-      break;
-    case DW_EH_PE_sdata2:
-      if (readp + 2 > endp)
-	goto invalid;
-      *res = read_2sbyte_unaligned_inc (dbg, readp);
-      break;
-    case DW_EH_PE_sdata4:
-      if (readp + 4 > endp)
-	goto invalid;
-      *res = read_4sbyte_unaligned_inc (dbg, readp);
-      break;
-    case DW_EH_PE_sdata8:
-      if (readp + 8 > endp)
-	goto invalid;
-      *res = read_8sbyte_unaligned_inc (dbg, readp);
-      break;
-    default:
-    invalid:
-      error (1, 0,
-	     gettext ("invalid encoding"));
-    }
-
-  return readp;
-}
-
-
 static void
 print_debug_frame_section (Dwfl_Module *dwflmod, Ebl *ebl, GElf_Ehdr *ehdr,
 			   Elf_Scn *scn, GElf_Shdr *shdr, Dwarf *dbg)
@@ -5851,7 +5852,7 @@ print_debug_frame_section (Dwfl_Module *dwflmod, Ebl *ebl, GElf_Ehdr *ehdr,
       else
 	print_cfa_program (readp, cieend, vma_base, code_alignment_factor,
 			   data_alignment_factor, version, ptr_size,
-			   dwflmod, ebl, dbg);
+			   fde_encoding, dwflmod, ebl, dbg);
       readp = cieend;
     }
 }

Ben, do you happen to have a testcase around for this?

Thanks,

Mark