Re: Prelinking on ARM with Debug Link

[Torsten Polle <Torsten.Polle@gmx.de>]

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Am 18.02.2016 um 17:21 schrieb Mark Wielaard <mjw@redhat.com>:
> 
> On Tue, 2016-02-16 at 21:46 +0100, Torsten Polle wrote:
>> The target architecture is 32bit ARM. The host architecture is 64bit
>> X86. That’s the reason why field .sec_load_offset is initialised with
>> a 64bit wide hexadecimal number. But as the field .sec_load_offset is
>> defined only as „unsigned long“, the compiler complains. As a work
>> around I tried to output decimal number instead for the initialisation
>> of .sec_load_offset. I can compile alright. But the resulting
>> backtrace calculations shown in my previous example produce strange
>> results.
> 
> OK, I don't have such a setup, but maybe all that is needed, if we
> assume negative values are ok, is to not write sec_load_offset out in
> hex, but simply in dec. Could you try the attached patch?
> 
> Thanks,
> 
> Mark

Hi Mark,

the principle idea of your patch works. But I had to rewrite it to really work in my environment. Could you please have a look at my proposal? Would something like that be acceptable?

I would like to double check in my environment if we could fall back to the hex notation again.

Thanks,
Torsten

[-- Attachment #2: 0001-Fix-Compilation-fails-for-prelinked-libraries.patch --]
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From c2854c6c8400ae3658e6037d2a0bc656ee550a33 Mon Sep 17 00:00:00 2001
Message-Id: <c2854c6c8400ae3658e6037d2a0bc656ee550a33.1456177234.git.Torsten.Polle@gmx.de>
From: Torsten Polle <Torsten.Polle@gmx.de>
Date: Mon, 22 Feb 2016 22:39:59 +0100
Subject: [PATCH] Fix: Compilation fails for prelinked libraries.

The offset to the section ".text" in a prelinked library might increase due to
changed relocations that need more space. If the prelinked library contains a
debug link and the linked file is not prelinked, the offset to the ".text"
section is different. If the difference between the offset of the ".text"
section in the prelinked library and non-prelinked library (with e.g. debug
information) becomes negative, the representation of this negative number has
to fit into an "unsigned int". If the width of the host is larger than the
width of the target, the compilation for the target fails.

Signed-off-by: Torsten Polle <Torsten.Polle@gmx.de>
---
 translate.cxx |   34 ++++++++++++++++++++++++++++++----
 1 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/translate.cxx b/translate.cxx
index f792343..f0364e9 100644
--- a/translate.cxx
+++ b/translate.cxx
@@ -6844,9 +6844,22 @@ dump_unwindsym_cxt (Dwfl_Module *m,
           c->output << ".debug_hdr_len = " << debug_frame_hdr_len << ", \n";
 
 	  Dwarf_Addr dwbias = 0;
+	  Dwarf_Addr elf_bias;
+	  GElf_Ehdr *ehdr, ehdr_mem;
+	  Elf *elf;
+	  elf = dwfl_module_getelf(m, &elf_bias);
+	  ehdr = gelf_getehdr(elf, &ehdr_mem);
 	  dwfl_module_getdwarf (m, &dwbias);
-	  c->output << ".sec_load_offset = 0x"
-		    << hex << debug_frame_off - dwbias << dec << "\n";
+	  if (ehdr->e_ident[EI_CLASS] == ELFCLASS32)
+	    {
+	      c->output << ".sec_load_offset = "
+			<< (uint32_t)debug_frame_off - (uint32_t)dwbias << "u\n";
+	    }
+	  else
+	    {
+	      c->output << ".sec_load_offset = 0x"
+			<< hex << debug_frame_off - dwbias << dec << "\n";
+	    }
 
 	  c->output << "#else\n";
 	  c->output << ".debug_hdr = NULL,\n";
@@ -6864,9 +6877,22 @@ dump_unwindsym_cxt (Dwfl_Module *m,
             {
               c->output << "#if defined(STP_NEED_LINE_DATA)\n";
               Dwarf_Addr dwbias = 0;
+	      Dwarf_Addr elf_bias;
+	      GElf_Ehdr *ehdr, ehdr_mem;
+	      Elf *elf;
+	      elf = dwfl_module_getelf(m, &elf_bias);
+	      ehdr = gelf_getehdr(elf, &ehdr_mem);
               dwfl_module_getdwarf (m, &dwbias);
-              c->output << ".sec_load_offset = 0x"
-                        << hex << debug_frame_off - dwbias << dec << "\n";
+	      if (ehdr->e_ident[EI_CLASS] == ELFCLASS32)
+		{
+		  c->output << ".sec_load_offset = "
+			    << (uint32_t)debug_frame_off - (uint32_t)dwbias << "u\n";
+		}
+	      else
+		{
+		  c->output << ".sec_load_offset = 0x"
+			    << hex << debug_frame_off - dwbias << dec << "\n";
+		}
               c->output << "#else\n";
             }
 	  c->output << ".sec_load_offset = 0\n";
-- 
1.7.4.1