Port the util library to Android

With this change, it is possible to build crashpad_util for Android with
clang. I built with NDK 13b (clang 3.8) at API 24 (current), API 21
(used by Chrome in 64-bit builds), and API 16 (used by Chrome in 32-bit
builds).

 - In WeakFileHandleFileWriter::WriteIoVec(): Android does not expose
   the IOV_MAX macro, but its value can be obtained by calling
   sysconf(_SC_IOV_MAX).
 - In CloseMultipleNowOrOnExec(): API 21 removes getdtablesize(). Skip
   it, because it returned the same thing as sysconf(_SC_OPEN_MAX),
   which is already consulted.
 - Throughout: Various #ifdefs checking for OS_LINUX have been extended
   to also check for OS_ANDROID. In Chrome’s build_config.h (and thus
   mini_chromium’s), OS_LINUX is not defined when OS_ANDROID is.

This has not been tested beyond building the crashpad_util target.

BUG=crashpad:30

Change-Id: Ieb0bed736029d2d776c534e30e534f186e6fb663
Reviewed-on: https://chromium-review.googlesource.com/405267
Reviewed-by: Robert Sesek <rsesek@chromium.org>

util/file/file_writer.cc

@@ -73,9 +73,19 @@ bool WeakFileHandleFileWriter::WriteIoVec(std::vector<WritableIoVec>* iovecs) {
   iovec* iov = reinterpret_cast<iovec*>(&(*iovecs)[0]);
   size_t remaining_iovecs = iovecs->size();
 
+#if defined(OS_ANDROID)
+  // Android does not expose the IOV_MAX macro, but makes its value available
+  // via sysconf(). See Android 7.0.0 bionic/libc/bionic/sysconf.cpp sysconf().
+  // Bionic defines IOV_MAX at bionic/libc/include/limits.h, but does not ship
+  // this file to the NDK as <limits.h>, substituting
+  // bionic/libc/include/bits/posix_limits.h.
+  const size_t kIovMax = sysconf(_SC_IOV_MAX);
+#else
+  const size_t kIovMax = IOV_MAX;
+#endif
+
   while (size > 0) {
-    size_t writev_iovec_count =
-        std::min(remaining_iovecs, implicit_cast<size_t>(IOV_MAX));
+    size_t writev_iovec_count = std::min(remaining_iovecs, kIovMax);
     ssize_t written =
         HANDLE_EINTR(writev(file_handle_, iov, writev_iovec_count));
     if (written < 0) {

util/misc/uuid.cc

@@ -111,7 +111,7 @@ bool UUID::InitializeWithNew() {
   }
   InitializeFromSystemUUID(&system_uuid);
   return true;
-#elif defined(OS_LINUX)
+#elif defined(OS_LINUX) || defined(OS_ANDROID)
   // Linux does not provide a UUID generator in a widely-available system
   // library. uuid_generate() from libuuid is not available everywhere.
   base::RandBytes(this, sizeof(*this));

util/posix/close_multiple.cc

@@ -88,7 +88,7 @@ using ScopedDIR = std::unique_ptr<DIR, ScopedDIRCloser>;
 bool CloseMultipleNowOrOnExecUsingFDDir(int fd, int preserve_fd) {
 #if defined(OS_MACOSX)
   const char kFDDir[] = "/dev/fd";
-#elif defined(OS_LINUX)
+#elif defined(OS_LINUX) || defined(OS_ANDROID)
   const char kFDDir[] = "/proc/self/fd";
 #endif
 
@@ -167,9 +167,17 @@ void CloseMultipleNowOrOnExec(int fd, int preserve_fd) {
   // Libc-1082.50.1/gen/FreeBSD/sysconf.c sysconf() and 10.11.6
   // xnu-3248.60.10/bsd/kern/kern_descrip.c getdtablesize(). For Linux glibc,
   // see glibc-2.24/sysdeps/posix/sysconf.c __sysconf() and
-  // glibc-2.24/sysdeps/posix/getdtsz.c __getdtablesize().
+  // glibc-2.24/sysdeps/posix/getdtsz.c __getdtablesize(). For Android, see
+  // 7.0.0 bionic/libc/bionic/sysconf.cpp sysconf() and
+  // bionic/libc/bionic/ndk_cruft.cpp getdtablesize().
   int max_fd = implicit_cast<int>(sysconf(_SC_OPEN_MAX));
+
+#if !defined(OS_ANDROID)
+  // getdtablesize() was removed effective Android 5.0.0 (API 21). Since it
+  // returns the same thing as the sysconf() above, just skip it. See
+  // https://android.googlesource.com/platform/bionic/+/462abab12b074c62c0999859e65d5a32ebb41951.
   max_fd = std::max(max_fd, getdtablesize());
+#endif
 
 #if !defined(OS_LINUX) || defined(OPEN_MAX)
   // Linux does not provide OPEN_MAX. See
@@ -198,7 +206,7 @@ void CloseMultipleNowOrOnExec(int fd, int preserve_fd) {
   } else {
     PLOG(WARNING) << "sysctl";
   }
-#elif defined(OS_LINUX)
+#elif defined(OS_LINUX) || defined(OS_ANDROID)
   // See linux-4.4.27/fs/file.c sysctl_nr_open, referenced by kernel/sys.c
   // do_prlimit() and kernel/sysctl.c fs_table. Inability to open this file is
   // not considered an error, because /proc may not be available or usable.

util/posix/drop_privileges.cc

@@ -71,7 +71,7 @@ void DropPrivileges() {
       CHECK_EQ(setegid(egid), -1);
     }
   }
-#elif defined(OS_LINUX)
+#elif defined(OS_LINUX) || defined(OS_ANDROID)
   PCHECK(setresgid(gid, gid, gid) == 0) << "setresgid";
   PCHECK(setresuid(uid, uid, uid) == 0) << "setresuid";
 

util/posix/symbolic_constants_posix.cc

@@ -14,9 +14,9 @@
 
 #include "util/posix/symbolic_constants_posix.h"
 
+#include <signal.h>
 #include <string.h>
 #include <sys/types.h>
-#include <sys/signal.h>
 
 #include "base/macros.h"
 #include "base/strings/stringprintf.h"
@@ -64,7 +64,7 @@ const char* kSignalNames[] = {
     "INFO",
     "USR1",
     "USR2",
-#elif defined(OS_LINUX)
+#elif defined(OS_LINUX) || defined(OS_ANDROID)
     // sed -Ene 's/^#define[[:space:]]SIG([[:alnum:]]+)[[:space:]]+[[:digit:]]{1,2}([[:space:]]|$).*/    "\1",/p'
     //     /usr/include/asm-generic/signal.h
     // and fix up by removing SIGIOT, SIGLOST, SIGUNUSED, and SIGRTMIN.
@@ -101,7 +101,7 @@ const char* kSignalNames[] = {
     "SYS",
 #endif
 };
-#if defined(OS_LINUX)
+#if defined(OS_LINUX) || defined(OS_ANDROID)
 // NSIG is 64 to account for real-time signals.
 static_assert(arraysize(kSignalNames) == 32, "kSignalNames length");
 #else

util/posix/symbolic_constants_posix_test.cc

@@ -65,7 +65,7 @@ const struct {
 #if defined(OS_MACOSX)
     {SIGEMT, "SIGEMT", "EMT"},
     {SIGINFO, "SIGINFO", "INFO"},
-#elif defined(OS_LINUX)
+#elif defined(OS_LINUX) || defined(OS_ANDROID)
     {SIGPWR, "SIGPWR", "PWR"},
     {SIGSTKFLT, "SIGSTKFLT", "STKFLT"},
 #endif
@@ -120,7 +120,7 @@ TEST(SymbolicConstantsPOSIX, SignalToString) {
                        kSignalTestData[index].short_name);
   }
 
-#if defined(OS_LINUX)
+#if defined(OS_LINUX) || defined(OS_ANDROID)
   // NSIG is 64 to account for real-time signals.
   const int kSignalCount = 32;
 #else