Make abort messages available to debuggerd.

This adds __libc_fatal, cleans up the internal logging code a bit more,
and switches suitable callers over to __libc_fatal. In addition to logging,
__libc_fatal stashes the message somewhere that the debuggerd signal handler
can find it before calling abort.

In the debuggerd signal handler, we pass this address to debuggerd so that
it can come back with ptrace to read the message and present it to the user.

Bug: 8531731
Change-Id: I416ec1da38a8a1b0d0a582ccd7c8aaa681ed4a29
diff --git a/linker/linker.cpp b/linker/linker.cpp
index 3afd314..47c45eb 100644
--- a/linker/linker.cpp
+++ b/linker/linker.cpp
@@ -105,6 +105,8 @@
 
 __LIBC_HIDDEN__ int gLdDebugVerbosity;
 
+__LIBC_HIDDEN__ abort_msg_t* gAbortMessage = NULL; // For debuggerd.
+
 enum RelocationKind {
     kRelocAbsolute = 0,
     kRelocRelative,
@@ -171,8 +173,7 @@
  */
 extern "C" void __attribute__((noinline)) __attribute__((visibility("default"))) rtld_db_dlactivity();
 
-static r_debug _r_debug = {1, NULL, &rtld_db_dlactivity,
-                                  RT_CONSISTENT, 0};
+static r_debug _r_debug = {1, NULL, &rtld_db_dlactivity, RT_CONSISTENT, 0};
 static link_map_t* r_debug_tail = 0;
 
 static pthread_mutex_t gDebugMutex = PTHREAD_MUTEX_INITIALIZER;
@@ -1815,8 +1816,8 @@
 
   Elf32_Addr linker_addr = args.getauxval(AT_BASE);
 
-  Elf32_Ehdr *elf_hdr = (Elf32_Ehdr*) linker_addr;
-  Elf32_Phdr *phdr = (Elf32_Phdr*)((unsigned char*) linker_addr + elf_hdr->e_phoff);
+  Elf32_Ehdr* elf_hdr = (Elf32_Ehdr*) linker_addr;
+  Elf32_Phdr* phdr = (Elf32_Phdr*)((unsigned char*) linker_addr + elf_hdr->e_phoff);
 
   soinfo linker_so;
   memset(&linker_so, 0, sizeof(soinfo));
@@ -1841,6 +1842,7 @@
 
   // We have successfully fixed our own relocations. It's safe to run
   // the main part of the linker now.
+  args.abort_message_ptr = &gAbortMessage;
   Elf32_Addr start_address = __linker_init_post_relocation(args, linker_addr);
 
   set_soinfo_pool_protection(PROT_READ);