File systemtap-prioritize-symbol-table-lookup-for-pp... of Package systemtap-docs.2327

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File systemtap-prioritize-symbol-table-lookup-for-ppc64le.patch of Package systemtap-docs.2327

From: Hemant Kumar <hemant@linux.vnet.ibm.com>
Date: Mon Apr 20 15:59:24 2015 +0530
Subject: Prioritize symbol table lookup for ppc64le
Git-commit: b4c6a4b1cd00fd1681d76de6850a88aa516c4fef
References: FATE#319125
Signed-off-by: Tony Jones <tonyj@suse.de>

Prioritize symbol table lookup for ppc64le
    
    PPC64 ELF ABI v2 has a Global entry point and a local entry point
    for the functions. We need the Local entry point in order to probe
    these functions. However, the DIE for these functions in debuginfo
    return the function.entrypc which is same as the global entry point.
    The local entry point is not encoded in the debuginfo of the ELFs. The
    offset to local entry point is however encoded in the st_other field
    of these symbols in the symbol table.
    We need to use this field to adjust the sym.st_value to actually point
    to the local entry point instead of the global entry point.
    
    This patch is in relation to this bug :
    https://sourceware.org/bugzilla/show_bug.cgi?id=17638
    
    So, while adding symbols to the sym_table, we add an offset of
    PPC64_LOCAL_ENTRY_OFFSET(sym.st_other) to st_value.
    And when the function address is queried in query_dwarf_func(), we give
    priority to the cached sym_table, where we can retrieve the adjusted
    entry address of the function. If we don't get any address from the
    symbol table, then we proceed to get from the debuginfo.
    
    Macro definition PPC64_LOCAL_ENTRY_OFFSET has been picked up from glibc.
    It won't be defined if we are building systemtap on a machine having
    older elf.h and hence, won't recognize PPC64_LOCAL_ENTRY_OFFSET.
    
    Signed-off-by: Hemant Kumar <hemant@linux.vnet.ibm.com>

diff --git a/tapsets.cxx b/tapsets.cxx
index 639ac12..4633cb9 100644
--- a/tapsets.cxx
+++ b/tapsets.cxx
@@ -66,7 +66,17 @@ extern "C" {
 using namespace std;
 using namespace __gnu_cxx;
 
-
+// for elf.h where PPC64_LOCAL_ENTRY_OFFSET isn't defined
+#ifndef PPC64_LOCAL_ENTRY_OFFSET
+#define STO_PPC64_LOCAL_BIT    5
+#define STO_PPC64_LOCAL_MASK   (7 << STO_PPC64_LOCAL_BIT)
+#define PPC64_LOCAL_ENTRY_OFFSET(other)					\
+ (((1 << (((other) & STO_PPC64_LOCAL_MASK) >> STO_PPC64_LOCAL_BIT)) >> 2) << 2)
+#endif
+// for elf.h where EF_PPC64_ABI isn't defined
+#ifndef EF_PPC64_ABI
+#define EF_PPC64_ABI 3
+#endif
 
 // ------------------------------------------------------------------------
 
@@ -2050,6 +2060,18 @@ query_dwarf_inline_instance (Dwarf_Die * die, dwarf_query * q)
     }
 }
 
+static bool
+is_filtered_func_exists (func_info_map_t filtered, func_info *fi)
+{
+  for (unsigned i = 0; i < filtered.size(); i++)
+    {
+      if ((filtered[i].entrypc == fi->entrypc) && (filtered[i].name == fi->name))
+        return true;
+    }
+
+  return false;
+}
+
 static int
 query_dwarf_func (Dwarf_Die * func, dwarf_query * q)
 {
@@ -2100,7 +2122,35 @@ query_dwarf_func (Dwarf_Die * func, dwarf_query * q)
           q->dw.function_line (&func.decl_line);
 
           Dwarf_Addr entrypc;
-          if (q->dw.function_entrypc (&entrypc))
+
+          func.entrypc = 0;
+          Dwarf_Addr bias;
+          Dwfl_Module *mod = q->dw.module;
+          Elf* elf = (dwarf_getelf (dwfl_module_getdwarf (mod, &bias))
+                     ?: dwfl_module_getelf (mod, &bias));
+
+          GElf_Ehdr ehdr_mem;
+          GElf_Ehdr* em = gelf_getehdr (elf, &ehdr_mem);
+          if (em == NULL) throw SEMANTIC_ERROR (_("Couldn't get elf header"));
+
+          /* Giving priority to sym_table for ppc64*/
+          if ((em->e_machine == EM_PPC64) && ((em->e_flags & EF_PPC64_ABI) == 2)
+              && (q->dw.mod_info->sym_table))
+            {
+              set<func_info *> *fis;
+              fis = q->dw.mod_info->sym_table->lookup_symbol(func.name);
+              if (fis && !fis->empty())
+                {
+                  for (set<func_info*>::iterator it=fis->begin(); it!=fis->end() ; ++it)
+                    {
+                      func.entrypc = (*it)->addr;
+                      if (is_filtered_func_exists(q->filtered_functions, &func))
+                        continue;
+                      q->filtered_functions.push_back(func);
+                    }
+                }
+            }
+          else if (!func.entrypc && q->dw.function_entrypc (&entrypc))
             {
               func.entrypc = entrypc;
               q->filtered_functions.push_back (func);
@@ -8140,6 +8190,14 @@ symbol_table::get_from_elf()
   int syments = dwfl_module_getsymtab(mod);
   assert(syments);
   prepare_section_rejection(mod);
+  Dwarf_Addr bias;
+  Elf* elf = (dwarf_getelf (dwfl_module_getdwarf (mod, &bias))
+              ?: dwfl_module_getelf (mod, &bias));
+
+  GElf_Ehdr ehdr_mem;
+  GElf_Ehdr* em = gelf_getehdr (elf, &ehdr_mem);
+  if (em == NULL) throw SEMANTIC_ERROR (_("Couldn't get elf header"));
+
   for (int i = 1; i < syments; ++i)
     {
       GElf_Sym sym;
@@ -8168,6 +8226,16 @@ symbol_table::get_from_elf()
       addr = sym.st_value;
       reject = reject_section(section);
 #endif
+     /*
+      * For ELF ABI v2 on PPC64 LE, we need to adjust sym.st_value corresponding
+      * to the bits of sym.st_other. These bits will tell us what's the offset
+      * of the local entry point from the global entry point.
+      *
+      * st_other field is currently only used with ABIv2 on ppc64
+      */
+      if ((em->e_machine == EM_PPC64) && ((em->e_flags & EF_PPC64_ABI) == 2)
+          && (GELF_ST_TYPE(sym.st_info) == STT_FUNC) && sym.st_other)
+        addr += PPC64_LOCAL_ENTRY_OFFSET(sym.st_other);
 
       if (name && GELF_ST_TYPE(sym.st_info) == STT_FUNC)
         add_symbol(name, (GELF_ST_BIND(sym.st_info) == STB_WEAK),

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