This change adds an API to allow setting the flag to indicate that the profile data has been dumped to the file.

[liaoyuke]

Summary

The main use is for users to disable dumping profile data to the file
for certain processes in case the processes don't have permission to
write to the disks, and trying to do so would result in side effects
such as crashes.

Patch by Yuke Liao (@liaoyuke).

Additional context (Chromium use case):

• https://bugs.chromium.org/p/chromium/issues/detail?id=842424
• https://bugs.chromium.org/p/chromium/issues/detail?id=957655
• https://chromium-review.googlesource.com/c/chromium/src/+/1610093

[liaoyuke]

Please take a look. Thank you very much!

[Dor1s]

The change looks good to me, with one minor edit requested.

compiler-rt/lib/profile/InstrProfiling.c

39

I think it's better to call lprofSetProfileDumped here, just to make sure we keep the implementation at one place, i.e. inside internal lprofSetProfileDumped function (even though it's exported as well).

[liaoyuke]

• Use lprofSetProfileDumped

[davidxl]

lgtm

[Dor1s]

Getting ready to commit

compiler-rt/lib/profile/InstrProfiling.h

  * or if that's not set,  \c "default.profraw".
  */
 int __llvm_profile_write_file(void);
 
 int __llvm_orderfile_write_file(void);
 /*!
  * \brief this is a wrapper interface to \c __llvm_profile_write_file.
  * After this interface is invoked, a arleady dumped flag will be set
- * so that profile won't be dumped again during program exit. 
+ * so that profile won't be dumped again during program exit.
  * Invocation of interface __llvm_profile_reset_counters will clear
  * the flag. This interface is designed to be used to collect profile
  * data from user selected hot regions. The use model is
  *      __llvm_profile_reset_counters();
  *      ... hot region 1
  *      __llvm_profile_dump();
  *      .. some other code
  *      __llvm_profile_reset_counters();

 /*! \brief Get the version of the file format. */
 uint64_t __llvm_profile_get_version(void);
 
 /*! \brief Get the number of entries in the profile data section. */
 uint64_t __llvm_profile_get_data_size(const __llvm_profile_data *Begin,
                                       const __llvm_profile_data *End);
 
 /*!
+ * \brief Set the flag that profile data has been dumped to the file.
+ * This is useful for users to disable dumping profile data to the file for
+ * certain processes in case the processes don't have permission to write to
+ * the disks, and trying to do so would result in side effects such as crashes.
+ */
+void __llvm_profile_set_dumped();
+
+/*!
  * This variable is defined in InstrProfilingRuntime.cc as a hidden
  * symbol. Its main purpose is to enable profile runtime user to
  * bypass runtime initialization code -- if the client code explicitly
  * define this variable, then InstProfileRuntime.o won't be linked in.
  * Note that this variable's visibility needs to be hidden so that the
  * definition of this variable in an instrumented shared library won't
  * affect runtime initialization decision of the main program.
  *  __llvm_profile_profile_runtime. */

compiler-rt/lib/profile/InstrProfiling.c

 COMPILER_RT_VISIBILITY unsigned lprofProfileDumped() {
   return ProfileDumped;
 }
 
 COMPILER_RT_VISIBILITY void lprofSetProfileDumped() {
   ProfileDumped = 1;
 }
 
+COMPILER_RT_VISIBILITY void __llvm_profile_set_dumped() {
+  lprofSetProfileDumped();
+}
+
 /* Return the number of bytes needed to add to SizeInBytes to make it
  *   the result a multiple of 8.
  */
 COMPILER_RT_VISIBILITY uint8_t
 __llvm_profile_get_num_padding_bytes(uint64_t SizeInBytes) {
   return 7 & (sizeof(uint64_t) - SizeInBytes % sizeof(uint64_t));
 }