Re: Failures with exelib.exp testcase (was Re: minutes 2010-08-19)

["K.Prasad" <prasad at linux dot vnet dot ibm dot com>]

On Mon, Feb 14, 2011 at 09:33:26PM +0100, Mark Wielaard wrote:
> On Mon, 2011-02-14 at 22:19 +0530, K.Prasad wrote:
> > On Tue, Feb 08, 2011 at 02:13:35PM +0100, Mark Wielaard wrote:
> > > On Thu, 2011-02-03 at 10:59 -0800, Roland McGrath wrote:
> > > > What you need to do is:
> > > > 
> > > > 	Elf64_Addr opd_addr;
> > > > 	Dwarf_Addr bias;
> > > > 	Elf_Scn *opd = dwfl_module_address_section (mod, &sym_addr, &bias);
> > > > 	if (opd == NULL) ...;
> > > > 	Elf_Data *data = elf_rawdata (opd, NULL);
> > > > 	if (data == NULL) ...;
> > > > 	Elf_Data in, out;
> > > > 	out.d_buf = &final_addr;
> > > > 	in.d_buf = (char *) data->d_buf + sym_addr;
> > > > 	out.d_size = in.d_size = sizeof (Elf64_Addr);
> > > > 	out.d_type = in.d_type = ELF_T_ADDR;
> > > > 	if (elf64_xlatetom (elf, &out, &in, e_ident[EI_DATA]) == NULL) ...;
> > > > 	sym_addr = opd_addr + bias;
> > > 

So I made an attempt at turning the above piece of pseudocode into a patch
for systemtap/translate.cxx and here's what it turned out to be.

Upon execution the runtime experiences "Segmentation fault" at the line
if (elf64_xlatetom (&out, &in, elf_getident (elf, NULL)[EI_DATA]) != NULL)
and I'm trying to understand why.

Any suggestions or pointers to mistakes in creation of the patch are
welcome.

---
 translate.cxx |   25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

Index: systemtap/translate.cxx
===================================================================
--- systemtap.orig/translate.cxx
+++ systemtap/translate.cxx
@@ -5018,7 +5018,30 @@
 		    || sym.st_value >= end	// beyond current module,
 		    || sym.st_value < base))	// before first section.
             {
-              Dwarf_Addr sym_addr = sym.st_value;
+              Dwarf_Addr sym_addr;
+#ifdef __powerpc__
+//              Elf64_Addr opd_addr;
+              Dwarf_Addr bias;
+              Elf_Data *data = NULL;
+              Elf_Data in, out;
+              Elf_Scn *opd = dwfl_module_address_section (m, &sym_addr, &bias);
+              Elf* elf = (dwfl_module_getelf (m, &bias));
+
+              if (opd != NULL)
+                {
+                  data = elf_rawdata (opd, NULL);
+                  if (data == NULL)
+                      return DWARF_CB_ABORT;
+                }
+              out.d_buf = *userdata;
+              in.d_buf = (char *) data->d_buf + sym_addr;
+              out.d_size = in.d_size = sizeof (Elf64_Addr);
+              out.d_type = in.d_type = ELF_T_ADDR;
+              if (elf64_xlatetom (&out, &in, elf_getident (elf, NULL)[EI_DATA]) != NULL)
+                  sym_addr = sym.st_value + bias;
+#else
+              sym_addr = sym.st_value;
+#endif /* __powerpc__ */
               Dwarf_Addr save_addr = sym_addr;
               const char *secname = NULL;
 
Thanks,
K.Prasad