[profile] Add a mode to continuously sync counter updates to a file
Add support for continuously syncing profile counter updates to a file.
The motivation for this is that programs do not always exit cleanly. On
iOS, for example, programs are usually killed via a signal from the OS.
Running atexit() handlers after catching a signal is unreliable, so some
method for progressively writing out profile data is necessary.
The approach taken here is to mmap() the `__llvm_prf_cnts` section onto
a raw profile. To do this, the linker must page-align the counter and
data sections, and the runtime must ensure that counters are mapped to a
page-aligned offset within a raw profile.
Continuous mode is (for the moment) incompatible with the online merging
mode. This limitation is lifted in https://reviews.llvm.org/D69586.
Continuous mode is also (for the moment) incompatible with value
profiling, as I'm not sure whether there is interest in this and the
implementation may be tricky.
As I have not been able to test extensively on non-Darwin platforms,
only Darwin support is included for the moment. However, continuous mode
may "just work" without modification on Linux and some UNIX-likes. AIUI
the default value for the GNU linker's `--section-alignment` flag is set
to the page size on many systems. This appears to be true for LLD as
well, as its `no_nmagic` option is on by default. Continuous mode will
not "just work" on Fuchsia or Windows, as it's not possible to mmap() a
section on these platforms. There is a proposal to add a layer of
indirection to the profile instrumentation to support these platforms.
rdar://54210980
Differential Revision: https://reviews.llvm.org/D68351
diff --git a/compiler-rt/lib/profile/InstrProfilingFile.c b/compiler-rt/lib/profile/InstrProfilingFile.c
index 1b253c3..e2253de 100644
--- a/compiler-rt/lib/profile/InstrProfilingFile.c
+++ b/compiler-rt/lib/profile/InstrProfilingFile.c
@@ -32,6 +32,7 @@
#include "InstrProfiling.h"
#include "InstrProfilingInternal.h"
+#include "InstrProfilingPort.h"
#include "InstrProfilingUtil.h"
/* From where is profile name specified.
@@ -100,6 +101,12 @@
COMPILER_RT_VISIBILITY void __llvm_profile_set_file_object(FILE *File,
int EnableMerge) {
+ if (__llvm_profile_is_continuous_mode_enabled()) {
+ PROF_WARN("__llvm_profile_set_file_object(fd=%d) not supported, because "
+ "continuous sync mode (%%c) is enabled",
+ fileno(File));
+ return;
+ }
setProfileFile(File);
setProfileMergeRequested(EnableMerge);
}
@@ -347,6 +354,15 @@
if (lprofCurFilename.MergePoolSize)
return;
+ /* Only create the profile directory and truncate an existing profile once.
+ * In continuous mode, this is necessary, as the profile is written-to by the
+ * runtime initializer. */
+ const char *lprofInitOnceEnv = "__LLVM_PROFILE_RT_INIT_ONCE";
+ int initialized = getenv(lprofInitOnceEnv) != NULL;
+ if (initialized)
+ return;
+ setenv(lprofInitOnceEnv, lprofInitOnceEnv, 1);
+
createProfileDir(Filename);
/* Truncate the file. Later we'll reopen and append. */
@@ -356,6 +372,99 @@
fclose(File);
}
+static void initializeProfileForContinuousMode(void) {
+#if defined(__Fuchsia__) || defined(_WIN32)
+ PROF_ERR("%s\n", "Continuous mode not yet supported on Fuchsia or Windows.");
+#else // defined(__Fuchsia__) || defined(_WIN32)
+ if (!__llvm_profile_is_continuous_mode_enabled())
+ return;
+
+ /* Get the sizes of various profile data sections. Taken from
+ * __llvm_profile_get_size_for_buffer(). */
+ const __llvm_profile_data *DataBegin = __llvm_profile_begin_data();
+ const __llvm_profile_data *DataEnd = __llvm_profile_end_data();
+ const uint64_t *CountersBegin = __llvm_profile_begin_counters();
+ const uint64_t *CountersEnd = __llvm_profile_end_counters();
+ const char *NamesBegin = __llvm_profile_begin_names();
+ const char *NamesEnd = __llvm_profile_end_names();
+ const uint64_t NamesSize = (NamesEnd - NamesBegin) * sizeof(char);
+ uint64_t DataSize = __llvm_profile_get_data_size(DataBegin, DataEnd);
+ uint64_t CountersSize = CountersEnd - CountersBegin;
+
+ /* Check that the counter and data sections in this image are page-aligned. */
+ unsigned PageSize = getpagesize();
+ if ((intptr_t)CountersBegin % PageSize != 0) {
+ PROF_ERR("Counters section not page-aligned (start = %p, pagesz = %u).\n",
+ CountersBegin, PageSize);
+ return;
+ }
+ if ((intptr_t)DataBegin % PageSize != 0) {
+ PROF_ERR("Data section not page-aligned (start = %p, pagesz = %u).\n",
+ DataBegin, PageSize);
+ return;
+ }
+
+ /* Open the raw profile in append mode. */
+ int Length = getCurFilenameLength();
+ char *FilenameBuf = (char *)COMPILER_RT_ALLOCA(Length + 1);
+ const char *Filename = getCurFilename(FilenameBuf, 0);
+ if (!Filename)
+ return;
+ FILE *File = fopen(Filename, "a+b");
+ if (!File)
+ return;
+
+ int Fileno = fileno(File);
+
+ /* Check that the offset within the file is page-aligned. */
+ off_t CurrentFileOffset = ftello(File);
+ off_t OffsetModPage = CurrentFileOffset % PageSize;
+ if (OffsetModPage != 0) {
+ PROF_ERR("Continuous counter sync mode is enabled, but raw profile is not"
+ "page-aligned. CurrentFileOffset = %lld, pagesz = %u.\n",
+ CurrentFileOffset, PageSize);
+ return;
+ }
+
+ /* Determine how much padding is needed before/after the counters and after
+ * the names. */
+ uint64_t PaddingBytesBeforeCounters, PaddingBytesAfterCounters,
+ PaddingBytesAfterNames;
+ __llvm_profile_get_padding_sizes_for_counters(
+ DataSize, CountersSize, NamesSize, &PaddingBytesBeforeCounters,
+ &PaddingBytesAfterCounters, &PaddingBytesAfterNames);
+
+ uint64_t PageAlignedCountersLength =
+ (CountersSize * sizeof(uint64_t)) + PaddingBytesAfterCounters;
+ uint64_t FileOffsetToCounters =
+ CurrentFileOffset + sizeof(__llvm_profile_header) +
+ (DataSize * sizeof(__llvm_profile_data)) + PaddingBytesBeforeCounters;
+
+ /* Write the partial profile. This grows the file to a point where the mmap()
+ * can succeed. Leak the file handle, as the file should stay open. */
+ setProfileFile(File);
+ int rc = writeFile(Filename);
+ if (rc)
+ PROF_ERR("Failed to write file \"%s\": %s\n", Filename, strerror(errno));
+ setProfileFile(NULL);
+
+ uint64_t *CounterMmap = (uint64_t *)mmap(
+ (void *)CountersBegin, PageAlignedCountersLength, PROT_READ | PROT_WRITE,
+ MAP_FIXED | MAP_SHARED, Fileno, FileOffsetToCounters);
+ if (CounterMmap != CountersBegin) {
+ PROF_ERR(
+ "Continuous counter sync mode is enabled, but mmap() failed (%s).\n"
+ " - CountersBegin: %p\n"
+ " - PageAlignedCountersLength: %llu\n"
+ " - Fileno: %d\n"
+ " - FileOffsetToCounters: %llu\n",
+ strerror(errno), CountersBegin, PageAlignedCountersLength, Fileno,
+ FileOffsetToCounters);
+ return;
+ }
+#endif // defined(__Fuchsia__) || defined(_WIN32)
+}
+
static const char *DefaultProfileName = "default.profraw";
static void resetFilenameToDefault(void) {
if (lprofCurFilename.FilenamePat && lprofCurFilename.OwnsFilenamePat) {
@@ -419,12 +528,33 @@
FilenamePat);
return -1;
}
+ } else if (FilenamePat[I] == 'c') {
+ if (__llvm_profile_is_continuous_mode_enabled()) {
+ PROF_WARN("%%c specifier can only be specified once in %s.\n",
+ FilenamePat);
+ return -1;
+ }
+ if (MergingEnabled) {
+ PROF_WARN("%%c specifier can not be used with profile merging (%%m) "
+ "in %s.\n",
+ FilenamePat);
+ return -1;
+ }
+
+ __llvm_profile_enable_continuous_mode();
+ I++; /* advance to 'c' */
} else if (containsMergeSpecifier(FilenamePat, I)) {
if (MergingEnabled) {
PROF_WARN("%%m specifier can only be specified once in %s.\n",
FilenamePat);
return -1;
}
+ if (__llvm_profile_is_continuous_mode_enabled()) {
+ PROF_WARN("%%c specifier can not be used with profile merging (%%m) "
+ "in %s.\n",
+ FilenamePat);
+ return -1;
+ }
MergingEnabled = 1;
if (FilenamePat[I] == 'm')
lprofCurFilename.MergePoolSize = 1;
@@ -447,6 +577,7 @@
const char *OldFilenamePat = lprofCurFilename.FilenamePat;
ProfileNameSpecifier OldPNS = lprofCurFilename.PNS;
+ /* The old profile name specifier takes precedence over the old one. */
if (PNS < OldPNS)
return;
@@ -475,6 +606,7 @@
}
truncateCurrentFile();
+ initializeProfileForContinuousMode();
}
/* Return buffer length that is required to store the current profile
@@ -511,7 +643,8 @@
return 0;
if (!(lprofCurFilename.NumPids || lprofCurFilename.NumHosts ||
- lprofCurFilename.MergePoolSize)) {
+ lprofCurFilename.MergePoolSize ||
+ __llvm_profile_is_continuous_mode_enabled())) {
if (!ForceUseBuf)
return lprofCurFilename.FilenamePat;
@@ -646,6 +779,8 @@
*/
COMPILER_RT_VISIBILITY
void __llvm_profile_set_filename(const char *FilenamePat) {
+ if (__llvm_profile_is_continuous_mode_enabled())
+ return;
parseAndSetFilename(FilenamePat, PNS_runtime_api, 1);
}
@@ -660,7 +795,7 @@
char *FilenameBuf;
int PDeathSig = 0;
- if (lprofProfileDumped()) {
+ if (lprofProfileDumped() || __llvm_profile_is_continuous_mode_enabled()) {
PROF_NOTE("Profile data not written to file: %s.\n", "already written");
return 0;
}