GCC 7 libbacktrace patch committed: Ignore compressed debug sections

[Ian Lance Taylor]

This patch to the GCC 7 libbacktrace ignores compressed debug
sections.  If we don't, the DWARF reader reports an error.  Since the
GCC 7 libbacktrace does not support uncompressing the debug sections,
ignoring them is the best approach (on trunk, we uncompress).  This is
for PR 80914.  Bootstrapped and ran libbacktrace tests on
x86_64-pc-linux-gnu.  Committed to GCC 7 branch.

Ian

2017-10-10  Ian Lance Taylor  <i...@golang.org>

PR go/80914
* elf.c (SHF_COMPRESSED): Define.
(elf_add): Ignore debug sections with SHF_COMPRESSED set.

Index: elf.c
===================================================================
--- elf.c       (revision 253593)
+++ elf.c       (working copy)
@@ -103,6 +103,7 @@
 #undef SHT_SYMTAB
 #undef SHT_STRTAB
 #undef SHT_DYNSYM
+#undef SFH_COMPRESSED
 #undef STT_OBJECT
 #undef STT_FUNC
 
@@ -195,6 +196,8 @@
 #define SHT_STRTAB 3
 #define SHT_DYNSYM 11
 
+#define SHF_COMPRESSED 0x800
+
 #if BACKTRACE_ELF_SIZE == 32
 
 typedef struct
@@ -700,7 +703,8 @@
 
       for (j = 0; j < (int) DEBUG_MAX; ++j)
        {
-         if (strcmp (name, debug_section_names[j]) == 0)
+         if (strcmp (name, debug_section_names[j]) == 0
+              && (shdr->sh_flags & SHF_COMPRESSED) == 0)
            {
              sections[j].offset = shdr->sh_offset;
              sections[j].size = shdr->sh_size;