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[profile] Don't dump counters when forking and don't reset when calling exec** functions 

Summary:
There is no need to write out gcdas when forking because we can just reset the counters in the parent process.
Let say a counter is N before the fork, then fork and this counter is set to 0 in the child process.
In the parent process, the counter is incremented by P and in the child process it's incremented by C.
When dump is ran at exit, parent process will dump N+P for the given counter and the child process will dump 0+C, so when the gcdas are merged the resulting counter will be N+P+C.
About exec** functions, since the current process is replaced by an another one there is no need to reset the counters but just write out the gcdas since the counters are definitely lost.
To avoid to have lists in a bad state, we just lock them during the fork and the flush (if called explicitely) and lock them when an element is added.

Reviewers: marco-c

Reviewed By: marco-c

Subscribers: hiraditya, cfe-commits, #sanitizers, llvm-commits, sylvestre.ledru

Tags: #clang, #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D74953
This commit is contained in:
Calixte Denizet 2020-02-10 18:46:37 +01:00
parent 9b23024c8b
commit 8f46269f0c
3 changed files with 182 additions and 57 deletions
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2
clang/lib/Driver/ToolChains/Darwin.cpp
View File

@ -1144,8 +1144,10 @@ void Darwin::addProfileRTLibs(const ArgList &Args,
if (hasExportSymbolDirective(Args)) {
if (ForGCOV) {
addExportedSymbol(CmdArgs, "___gcov_flush");
addExportedSymbol(CmdArgs, "___gcov_fork");
addExportedSymbol(CmdArgs, "_flush_fn_list");
addExportedSymbol(CmdArgs, "_writeout_fn_list");
addExportedSymbol(CmdArgs, "_reset_fn_list");
} else {
addExportedSymbol(CmdArgs, "___llvm_profile_filename");
addExportedSymbol(CmdArgs, "___llvm_profile_raw_version");

94
compiler-rt/lib/profile/GCDAProfiling.c
View File

@ -32,8 +32,9 @@
#include <windows.h>
#include "WindowsMMap.h"
#else
#include <sys/mman.h>
#include <sys/file.h>
#include <sys/mman.h>
#include <unistd.h>
#endif
#if defined(__FreeBSD__) && defined(__i386__)
@ -62,27 +63,20 @@ typedef unsigned long long uint64_t;
#include "InstrProfiling.h"
#include "InstrProfilingUtil.h"
/* #define DEBUG_GCDAPROFILING */
#ifndef _WIN32
#include <pthread.h>
static pthread_mutex_t gcov_flush_mutex = PTHREAD_MUTEX_INITIALIZER;
static __inline void gcov_flush_lock() {
pthread_mutex_lock(&gcov_flush_mutex);
}
static __inline void gcov_flush_unlock() {
pthread_mutex_unlock(&gcov_flush_mutex);
}
pthread_mutex_t gcov_mutex = PTHREAD_MUTEX_INITIALIZER;
static __inline void gcov_lock() { pthread_mutex_lock(&gcov_mutex); }
static __inline void gcov_unlock() { pthread_mutex_unlock(&gcov_mutex); }
#else
#include <windows.h>
static SRWLOCK gcov_flush_mutex = SRWLOCK_INIT;
static __inline void gcov_flush_lock() {
AcquireSRWLockExclusive(&gcov_flush_mutex);
}
static __inline void gcov_flush_unlock() {
ReleaseSRWLockExclusive(&gcov_flush_mutex);
}
SRWLOCK gcov_mutex = SRWLOCK_INIT;
static __inline void gcov_lock() { AcquireSRWLockExclusive(&gcov_mutex); }
static __inline void gcov_unlock() { ReleaseSRWLockExclusive(&gcov_mutex); }
#endif
/* #define DEBUG_GCDAPROFILING */
/*
* --- GCOV file format I/O primitives ---
*/
@ -138,6 +132,12 @@ struct fn_list writeout_fn_list;
*/
struct fn_list flush_fn_list;
/*
* A list of reset functions that our __gcov_reset() function should call,
* shared between all dynamic objects.
*/
struct fn_list reset_fn_list;
static void fn_list_insert(struct fn_list* list, fn_ptr fn) {
struct fn_node* new_node = malloc(sizeof(struct fn_node));
new_node->fn = fn;
@ -638,8 +638,25 @@ void llvm_register_flush_function(fn_ptr fn) {
fn_list_insert(&flush_fn_list, fn);
}
COMPILER_RT_VISIBILITY
void llvm_register_reset_function(fn_ptr fn) {
fn_list_insert(&reset_fn_list, fn);
}
COMPILER_RT_VISIBILITY
void llvm_reset_counters(void) {
struct fn_node *curr = reset_fn_list.head;
while (curr) {
if (curr->id == CURRENT_ID) {
curr->fn();
}
curr = curr->next;
}
}
void __gcov_flush() {
gcov_flush_lock();
gcov_lock();
struct fn_node* curr = flush_fn_list.head;
@ -648,30 +665,69 @@ void __gcov_flush() {
curr = curr->next;
}
gcov_flush_unlock();
gcov_unlock();
}
#if !defined(_WIN32)
pid_t __gcov_fork() {
pid_t parent_pid = getpid();
pid_t pid;
gcov_lock();
// Avoid a concurrent modification of the lists during the fork.
// For example, a thread is making a fork while another one is
// loading a CU and so executing global initializer in this case
// the child process could inherit a bad list (e.g. bad tail)
// or could have the malloc in a wrong state.
pid = fork();
gcov_unlock();
if (pid == 0) {
pid_t child_pid = getpid();
if (child_pid != parent_pid) {
// The pid changed so we've a fork (one could have its own fork function)
// Just reset the counters for this child process
// No need to lock here since we just forked and cannot have any other
// threads.
llvm_reset_counters();
}
}
return pid;
}
#endif
COMPILER_RT_VISIBILITY
void llvm_delete_flush_function_list(void) {
fn_list_remove(&flush_fn_list);
}
COMPILER_RT_VISIBILITY
void llvm_gcov_init(fn_ptr wfn, fn_ptr ffn) {
void llvm_delete_reset_function_list(void) { fn_list_remove(&reset_fn_list); }
COMPILER_RT_VISIBILITY
void llvm_gcov_init(fn_ptr wfn, fn_ptr ffn, fn_ptr rfn) {
static int atexit_ran = 0;
gcov_lock();
if (wfn)
llvm_register_writeout_function(wfn);
if (ffn)
llvm_register_flush_function(ffn);
if (rfn)
llvm_register_reset_function(rfn);
gcov_unlock();
if (atexit_ran == 0) {
atexit_ran = 1;
/* Make sure we write out the data and delete the data structures. */
atexit(llvm_delete_flush_function_list);
atexit(llvm_delete_writeout_function_list);
atexit(llvm_delete_reset_function_list);
atexit(llvm_writeout_files);
}
}

143
llvm/lib/Transforms/Instrumentation/GCOVProfiling.cpp
View File

@ -115,7 +115,8 @@ private:
// list.
Function *
insertCounterWriteout(ArrayRef<std::pair<GlobalVariable *, MDNode *>>);
Function *insertFlush(ArrayRef<std::pair<GlobalVariable *, MDNode *>>);
Function *insertReset(ArrayRef<std::pair<GlobalVariable *, MDNode *>>);
Function *insertFlush(Function *ResetF);
void AddFlushBeforeForkAndExec();
@ -631,35 +632,74 @@ static bool shouldKeepInEntry(BasicBlock::iterator It) {
}
void GCOVProfiler::AddFlushBeforeForkAndExec() {
SmallVector<Instruction *, 2> ForkAndExecs;
SmallVector<std::pair<bool, CallInst *>, 2> ForkAndExecs;
for (auto &F : M->functions()) {
auto *TLI = &GetTLI(F);
for (auto &I : instructions(F)) {
if (CallInst *CI = dyn_cast<CallInst>(&I)) {
if (Function *Callee = CI->getCalledFunction()) {
LibFunc LF;
if (TLI->getLibFunc(*Callee, LF) &&
(LF == LibFunc_fork || LF == LibFunc_execl ||
LF == LibFunc_execle || LF == LibFunc_execlp ||
LF == LibFunc_execv || LF == LibFunc_execvp ||
LF == LibFunc_execve || LF == LibFunc_execvpe ||
LF == LibFunc_execvP)) {
ForkAndExecs.push_back(&I);
if (TLI->getLibFunc(*Callee, LF)) {
if (LF == LibFunc_fork) {
#if !defined(_WIN32)
ForkAndExecs.push_back({true, CI});
#endif
} else if (LF == LibFunc_execl || LF == LibFunc_execle ||
LF == LibFunc_execlp || LF == LibFunc_execv ||
LF == LibFunc_execvp || LF == LibFunc_execve ||
LF == LibFunc_execvpe || LF == LibFunc_execvP) {
ForkAndExecs.push_back({false, CI});
}
}
}
}
}
}
// We need to split the block after the fork/exec call
// because else the counters for the lines after will be
// the same as before the call.
for (auto I : ForkAndExecs) {
IRBuilder<> Builder(I);
FunctionType *FTy = FunctionType::get(Builder.getVoidTy(), {}, false);
FunctionCallee GCOVFlush = M->getOrInsertFunction("__gcov_flush", FTy);
Builder.CreateCall(GCOVFlush);
I->getParent()->splitBasicBlock(I);
for (auto F : ForkAndExecs) {
IRBuilder<> Builder(F.second);
BasicBlock *Parent = F.second->getParent();
auto NextInst = ++F.second->getIterator();
if (F.first) {
// We've a fork so just reset the counters in the child process
FunctionType *FTy = FunctionType::get(Builder.getInt32Ty(), {}, false);
FunctionCallee GCOVFork = M->getOrInsertFunction("__gcov_fork", FTy);
F.second->setCalledFunction(GCOVFork);
if (NextInst != Parent->end()) {
// We split just after the fork to have a counter for the lines after
// Anyway there's a bug:
// void foo() { fork(); }
// void bar() { foo(); blah(); }
// then "blah();" will be called 2 times but showed as 1
// because "blah()" belongs to the same block as "foo();"
Parent->splitBasicBlock(NextInst);
// back() is a br instruction with a debug location
// equals to the one from NextAfterFork
// So to avoid to have two debug locs on two blocks just change it
DebugLoc Loc = F.second->getDebugLoc();
Parent->back().setDebugLoc(Loc);
}
} else {
// Since the process is replaced by a new one we need to write out gcdas
// No need to reset the counters since they'll be lost after the exec**
FunctionType *FTy = FunctionType::get(Builder.getVoidTy(), {}, false);
FunctionCallee WriteoutF =
M->getOrInsertFunction("llvm_writeout_files", FTy);
Builder.CreateCall(WriteoutF);
if (NextInst != Parent->end()) {
DebugLoc Loc = F.second->getDebugLoc();
Builder.SetInsertPoint(&*NextInst);
// If the exec** fails we must reset the counters since they've been
// dumped
FunctionCallee ResetF =
M->getOrInsertFunction("llvm_reset_counters", FTy);
Builder.CreateCall(ResetF)->setDebugLoc(Loc);
Parent->splitBasicBlock(NextInst);
Parent->back().setDebugLoc(Loc);
}
}
}
}
@ -851,7 +891,8 @@ bool GCOVProfiler::emitProfileArcs() {
}
Function *WriteoutF = insertCounterWriteout(CountersBySP);
Function *FlushF = insertFlush(CountersBySP);
Function *ResetF = insertReset(CountersBySP);
Function *FlushF = insertFlush(ResetF);
// Create a small bit of code that registers the "__llvm_gcov_writeout" to
// be executed at exit and the "__llvm_gcov_flush" function to be executed
@ -869,16 +910,14 @@ bool GCOVProfiler::emitProfileArcs() {
IRBuilder<> Builder(BB);
FTy = FunctionType::get(Type::getVoidTy(*Ctx), false);
Type *Params[] = {
PointerType::get(FTy, 0),
PointerType::get(FTy, 0)
};
Type *Params[] = {PointerType::get(FTy, 0), PointerType::get(FTy, 0),
PointerType::get(FTy, 0)};
FTy = FunctionType::get(Builder.getVoidTy(), Params, false);
// Initialize the environment and register the local writeout and flush
// functions.
// Initialize the environment and register the local writeout, flush and
// reset functions.
FunctionCallee GCOVInit = M->getOrInsertFunction("llvm_gcov_init", FTy);
Builder.CreateCall(GCOVInit, {WriteoutF, FlushF});
Builder.CreateCall(GCOVInit, {WriteoutF, FlushF, ResetF});
Builder.CreateRetVoid();
appendToGlobalCtors(*M, F, 0);
@ -1191,8 +1230,43 @@ Function *GCOVProfiler::insertCounterWriteout(
return WriteoutF;
}
Function *GCOVProfiler::
insertFlush(ArrayRef<std::pair<GlobalVariable*, MDNode*> > CountersBySP) {
Function *GCOVProfiler::insertReset(
ArrayRef<std::pair<GlobalVariable *, MDNode *>> CountersBySP) {
FunctionType *FTy = FunctionType::get(Type::getVoidTy(*Ctx), false);
Function *ResetF = M->getFunction("__llvm_gcov_reset");
if (!ResetF)
ResetF = Function::Create(FTy, GlobalValue::InternalLinkage,
"__llvm_gcov_reset", M);
else
ResetF->setLinkage(GlobalValue::InternalLinkage);
ResetF->setUnnamedAddr(GlobalValue::UnnamedAddr::Global);
ResetF->addFnAttr(Attribute::NoInline);
if (Options.NoRedZone)
ResetF->addFnAttr(Attribute::NoRedZone);
BasicBlock *Entry = BasicBlock::Create(*Ctx, "entry", ResetF);
IRBuilder<> Builder(Entry);
// Zero out the counters.
for (const auto &I : CountersBySP) {
GlobalVariable *GV = I.first;
Constant *Null = Constant::getNullValue(GV->getValueType());
Builder.CreateStore(Null, GV);
}
Type *RetTy = ResetF->getReturnType();
if (RetTy == Type::getVoidTy(*Ctx))
Builder.CreateRetVoid();
else if (RetTy->isIntegerTy())
// Used if __llvm_gcov_reset was implicitly declared.
Builder.CreateRet(ConstantInt::get(RetTy, 0));
else
report_fatal_error("invalid return type for __llvm_gcov_reset");
return ResetF;
}
Function *GCOVProfiler::insertFlush(Function *ResetF) {
FunctionType *FTy = FunctionType::get(Type::getVoidTy(*Ctx), false);
Function *FlushF = M->getFunction("__llvm_gcov_flush");
if (!FlushF)
@ -1206,20 +1280,13 @@ insertFlush(ArrayRef<std::pair<GlobalVariable*, MDNode*> > CountersBySP) {
FlushF->addFnAttr(Attribute::NoRedZone);
BasicBlock *Entry = BasicBlock::Create(*Ctx, "entry", FlushF);
IRBuilder<> Builder(Entry);
// Write out the current counters.
Function *WriteoutF = M->getFunction("__llvm_gcov_writeout");
assert(WriteoutF && "Need to create the writeout function first!");
IRBuilder<> Builder(Entry);
Builder.CreateCall(WriteoutF, {});
// Zero out the counters.
for (const auto &I : CountersBySP) {
GlobalVariable *GV = I.first;
Constant *Null = Constant::getNullValue(GV->getValueType());
Builder.CreateStore(Null, GV);
}
Builder.CreateCall(WriteoutF);
Builder.CreateCall(ResetF);
Type *RetTy = FlushF->getReturnType();
if (RetTy == Type::getVoidTy(*Ctx))