Partially port the crashpad_client library to Linux/Android

This defines the global (per-module) CrashpadInfo structure properly on
Linux/Android, located via the “crashpad_info” section name.

Per the ELF specification, section names with a leading dot are reserved
for the system. Reading that, I realized that the same is true of Mach-O
sections with leading underscores, so this renames the section as used
on Mach-O from __DATA,__crashpad_info to __DATA,crashpad_info.

This change is sufficient to successfully build crashpad_client as a
static library on Linux/Android, but the library is incomplete. There’s
no platform-specific database implementation, no CaptureContext() or
CRASHPAD_SIMULATE_CRASH() implementation, and most notably, no
CrashpadClient implementation.

BUG=crashpad:30

Change-Id: I29df7b0f8ee1c79bf8a19502812f59d4b1577b85
Reviewed-on: https://chromium-review.googlesource.com/406427
Reviewed-by: Robert Sesek <rsesek@chromium.org>

client/crashpad_info.cc

@@ -59,33 +59,47 @@ union Compile_Assert {
 // This may result in a static module initializer in debug-mode builds, but
 // because it’s POD, no code should need to run to initialize this under
 // release-mode optimization.
-#if defined(OS_MACOSX)
+#if defined(OS_POSIX)
+__attribute__((
+
+    // Put the structure in a well-known section name where it can be easily
+    // found without having to consult the symbol table.
+#if defined(OS_MACOSX)
+    section(SEG_DATA ",crashpad_info"),
+#elif defined(OS_LINUX) || defined(OS_ANDROID)
+    section("crashpad_info"),
+#else  // !defined(OS_MACOSX) && !defined(OS_LINUX) && !defined(OS_ANDROID)
+#error Port
+#endif  // !defined(OS_MACOSX) && !defined(OS_LINUX) && !defined(OS_ANDROID)
 
-// Put the structure in __DATA,__crashpad_info where it can be easily found
-// without having to consult the symbol table. The “used” attribute prevents it
-// from being dead-stripped.
-__attribute__((section(SEG_DATA ",__crashpad_info"),
-               used,
-               visibility("hidden")
 #if __has_feature(address_sanitizer)
-// AddressSanitizer would add a trailing red zone of at least 32 bytes, which
+    // AddressSanitizer would add a trailing red zone of at least 32 bytes,
-// would be reflected in the size of the custom section. This confuses
+    // which would be reflected in the size of the custom section. This confuses
     // MachOImageReader::GetCrashpadInfo(), which finds that the section’s size
     // disagrees with the structure’s size_ field. By specifying an alignment
     // greater than the red zone size, the red zone will be suppressed.
-               ,
+    aligned(64),
-               aligned(64)
+#endif  // __has_feature(address_sanitizer)
-#endif
+
-             )) CrashpadInfo g_crashpad_info;
+    // The “used” attribute prevents the structure from being dead-stripped.
+    used,
+
+    // There’s no need to expose this as a public symbol from the symbol table.
+    // All accesses from the outside can locate the well-known section name.
+    visibility("hidden")))
 
 #elif defined(OS_WIN)
 
 // Put the struct in a section name CPADinfo where it can be found without the
 // symbol table.
 #pragma section("CPADinfo", read, write)
-__declspec(allocate("CPADinfo")) CrashpadInfo g_crashpad_info;
+__declspec(allocate("CPADinfo"))
 
-#endif
+#else  // !defined(OS_POSIX) && !defined(OS_WIN)
+#error Port
+#endif  // !defined(OS_POSIX) && !defined(OS_WIN)
+
+CrashpadInfo g_crashpad_info;
 
 // static
 CrashpadInfo* CrashpadInfo::GetCrashpadInfo() {

snapshot/mac/mach_o_image_reader.cc

@@ -477,7 +477,7 @@ bool MachOImageReader::GetCrashpadInfo(
 
   mach_vm_address_t crashpad_info_address;
   const process_types::section* crashpad_info_section =
-      GetSectionByName(SEG_DATA, "__crashpad_info", &crashpad_info_address);
+      GetSectionByName(SEG_DATA, "crashpad_info", &crashpad_info_address);
   if (!crashpad_info_section) {
     return false;
   }

snapshot/mac/mach_o_image_reader.h

@@ -270,8 +270,9 @@ class MachOImageReader {
   //! \brief Obtains the module’s CrashpadInfo structure.
   //!
   //! \return `true` on success, `false` on failure. If the module does not have
-  //!     a `__crashpad_info` section, this will return `false` without logging
+  //!     a `__DATA,crashpad_info` section, this will return `false` without
-  //!     any messages. Other failures will result in messages being logged.
+  //!     logging any messages. Other failures will result in messages being
+  //!     logged.
   bool GetCrashpadInfo(process_types::CrashpadInfo* crashpad_info) const;
 
  private:

snapshot/mac/process_types/crashpad_info.proctype

@@ -21,7 +21,7 @@
 // snapshot/mac/process_types.cc to produce process type struct definitions and
 // accessors.
 
-// Client Mach-O images will contain a __DATA,__crashpad_info section formatted
+// Client Mach-O images will contain a __DATA,crashpad_info section formatted
 // according to this structure.
 PROCESS_TYPE_STRUCT_BEGIN(CrashpadInfo)
   PROCESS_TYPE_STRUCT_MEMBER(uint32_t, signature)

snapshot/module_snapshot.h

@@ -184,7 +184,7 @@ class ModuleSnapshot {
   //! keys.”
   //!
   //! For Mac OS X snapshots, these annotations are found by interpreting the
-  //! `__DATA, __crashpad_info` section as `CrashpadInfo`. Clients can use the
+  //! `__DATA,crashpad_info` section as `CrashpadInfo`. Clients can use the
   //! Crashpad client interface to store annotations in this structure. Most
   //! annotations under the client’s direct control will be retrievable by this
   //! method. For clients such as Chrome, this includes the process type.