lib/profile/InstrProfilingPlatformLinux.c - llvm-project/compiler-rt - Git at Google

 /*===- InstrProfilingPlatformLinux.c - Profile data Linux platform ------===*\
 |*
 |* Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 |* See https://llvm.org/LICENSE.txt for license information.
 |* SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 |*
 \*===----------------------------------------------------------------------===*/

 #if defined(__linux__) || defined(__FreeBSD__) || defined(__Fuchsia__) || \
     (defined(__sun__) && defined(__svr4__)) || defined(__NetBSD__) || \
     defined(_AIX)

 #if !defined(_AIX)
 #include <elf.h>
 #include <link.h>
 #endif
 #include <stdlib.h>
 #include <string.h>

 #include "InstrProfiling.h"
 #include "InstrProfilingInternal.h"

 #if defined(__FreeBSD__) && !defined(ElfW)
 /*
  * FreeBSD's elf.h and link.h headers do not define the ElfW(type) macro yet.
  * If this is added to all supported FreeBSD versions in the future, this
  * compatibility macro can be removed.
  */
 #define ElfW(type) __ElfN(type)
 #endif

 #define PROF_DATA_START INSTR_PROF_SECT_START(INSTR_PROF_DATA_COMMON)
 #define PROF_DATA_STOP INSTR_PROF_SECT_STOP(INSTR_PROF_DATA_COMMON)
 #define PROF_NAME_START INSTR_PROF_SECT_START(INSTR_PROF_NAME_COMMON)
 #define PROF_NAME_STOP INSTR_PROF_SECT_STOP(INSTR_PROF_NAME_COMMON)
 #define PROF_CNTS_START INSTR_PROF_SECT_START(INSTR_PROF_CNTS_COMMON)
 #define PROF_CNTS_STOP INSTR_PROF_SECT_STOP(INSTR_PROF_CNTS_COMMON)
 #define PROF_ORDERFILE_START INSTR_PROF_SECT_START(INSTR_PROF_ORDERFILE_COMMON)
 #define PROF_VNODES_START INSTR_PROF_SECT_START(INSTR_PROF_VNODES_COMMON)
 #define PROF_VNODES_STOP INSTR_PROF_SECT_STOP(INSTR_PROF_VNODES_COMMON)

 /* Declare section start and stop symbols for various sections
  * generated by compiler instrumentation.
  */
 extern __llvm_profile_data PROF_DATA_START COMPILER_RT_VISIBILITY
     COMPILER_RT_WEAK;
 extern __llvm_profile_data PROF_DATA_STOP COMPILER_RT_VISIBILITY
     COMPILER_RT_WEAK;
 extern char PROF_CNTS_START COMPILER_RT_VISIBILITY COMPILER_RT_WEAK;
 extern char PROF_CNTS_STOP COMPILER_RT_VISIBILITY COMPILER_RT_WEAK;
 extern uint32_t PROF_ORDERFILE_START COMPILER_RT_VISIBILITY COMPILER_RT_WEAK;
 extern char PROF_NAME_START COMPILER_RT_VISIBILITY COMPILER_RT_WEAK;
 extern char PROF_NAME_STOP COMPILER_RT_VISIBILITY COMPILER_RT_WEAK;
 extern ValueProfNode PROF_VNODES_START COMPILER_RT_VISIBILITY COMPILER_RT_WEAK;
 extern ValueProfNode PROF_VNODES_STOP COMPILER_RT_VISIBILITY COMPILER_RT_WEAK;

 COMPILER_RT_VISIBILITY const __llvm_profile_data *
 __llvm_profile_begin_data(void) {
   return &PROF_DATA_START;
 }
 COMPILER_RT_VISIBILITY const __llvm_profile_data *
 __llvm_profile_end_data(void) {
   return &PROF_DATA_STOP;
 }
 COMPILER_RT_VISIBILITY const char *__llvm_profile_begin_names(void) {
   return &PROF_NAME_START;
 }
 COMPILER_RT_VISIBILITY const char *__llvm_profile_end_names(void) {
   return &PROF_NAME_STOP;
 }
 COMPILER_RT_VISIBILITY char *__llvm_profile_begin_counters(void) {
   return &PROF_CNTS_START;
 }
 COMPILER_RT_VISIBILITY char *__llvm_profile_end_counters(void) {
   return &PROF_CNTS_STOP;
 }
 COMPILER_RT_VISIBILITY uint32_t *__llvm_profile_begin_orderfile(void) {
   return &PROF_ORDERFILE_START;
 }

 COMPILER_RT_VISIBILITY ValueProfNode *
 __llvm_profile_begin_vnodes(void) {
   return &PROF_VNODES_START;
 }
 COMPILER_RT_VISIBILITY ValueProfNode *__llvm_profile_end_vnodes(void) {
   return &PROF_VNODES_STOP;
 }
 COMPILER_RT_VISIBILITY ValueProfNode *CurrentVNode = &PROF_VNODES_START;
 COMPILER_RT_VISIBILITY ValueProfNode *EndVNode = &PROF_VNODES_STOP;

 #ifdef NT_GNU_BUILD_ID
 static size_t RoundUp(size_t size, size_t align) {
   return (size + align - 1) & ~(align - 1);
 }

 /*
  * Write binary id length and then its data, because binary id does not
  * have a fixed length.
  */
 static int WriteOneBinaryId(ProfDataWriter *Writer, uint64_t BinaryIdLen,
                             const uint8_t *BinaryIdData,
                             uint64_t BinaryIdPadding) {
   ProfDataIOVec BinaryIdIOVec[] = {
       {&BinaryIdLen, sizeof(uint64_t), 1, 0},
       {BinaryIdData, sizeof(uint8_t), BinaryIdLen, 0},
       {NULL, sizeof(uint8_t), BinaryIdPadding, 1},
   };
   if (Writer->Write(Writer, BinaryIdIOVec,
                     sizeof(BinaryIdIOVec) / sizeof(*BinaryIdIOVec)))
     return -1;

   /* Successfully wrote binary id, report success. */
   return 0;
 }

 /*
  * Look for the note that has the name "GNU\0" and type NT_GNU_BUILD_ID
  * that contains build id. If build id exists, write binary id.
  *
  * Each note in notes section starts with a struct which includes
  * n_namesz, n_descsz, and n_type members. It is followed by the name
  * (whose length is defined in n_namesz) and then by the descriptor
  * (whose length is defined in n_descsz).
  *
  * Note sections like .note.ABI-tag and .note.gnu.build-id are aligned
  * to 4 bytes, so round n_namesz and n_descsz to the nearest 4 bytes.
  */
 static int WriteBinaryIdForNote(ProfDataWriter *Writer,
                                 const ElfW(Nhdr) * Note) {
   int BinaryIdSize = 0;
   const char *NoteName = (const char *)Note + sizeof(ElfW(Nhdr));
   if (Note->n_type == NT_GNU_BUILD_ID && Note->n_namesz == 4 &&
       memcmp(NoteName, "GNU\0", 4) == 0) {
     uint64_t BinaryIdLen = Note->n_descsz;
     const uint8_t *BinaryIdData =
         (const uint8_t *)(NoteName + RoundUp(Note->n_namesz, 4));
     uint8_t BinaryIdPadding = __llvm_profile_get_num_padding_bytes(BinaryIdLen);
     if (Writer != NULL && WriteOneBinaryId(Writer, BinaryIdLen, BinaryIdData,
                                            BinaryIdPadding) == -1)
       return -1;

     BinaryIdSize = sizeof(BinaryIdLen) + BinaryIdLen + BinaryIdPadding;
   }

   return BinaryIdSize;
 }

 /*
  * Helper function that iterates through notes section and find build ids.
  * If writer is given, write binary ids into profiles.
  * If an error happens while writing, return -1.
  */
 static int WriteBinaryIds(ProfDataWriter *Writer, const ElfW(Nhdr) * Note,
                           const ElfW(Nhdr) * NotesEnd) {
   int BinaryIdsSize = 0;
   while (Note < NotesEnd) {
     int OneBinaryIdSize = WriteBinaryIdForNote(Writer, Note);
     if (OneBinaryIdSize == -1)
       return -1;
     BinaryIdsSize += OneBinaryIdSize;

     /* Calculate the offset of the next note in notes section. */
     size_t NoteOffset = sizeof(ElfW(Nhdr)) + RoundUp(Note->n_namesz, 4) +
                         RoundUp(Note->n_descsz, 4);
     Note = (const ElfW(Nhdr) *)((const char *)(Note) + NoteOffset);
   }

   return BinaryIdsSize;
 }

 /*
  * Write binary ids into profiles if writer is given.
  * Return the total size of binary ids.
  * If an error happens while writing, return -1.
  */
 COMPILER_RT_VISIBILITY int __llvm_write_binary_ids(ProfDataWriter *Writer) {
   extern const ElfW(Ehdr) __ehdr_start __attribute__((visibility("hidden")));
   const ElfW(Ehdr) *ElfHeader = &__ehdr_start;
   const ElfW(Phdr) *ProgramHeader =
       (const ElfW(Phdr) *)((uintptr_t)ElfHeader + ElfHeader->e_phoff);

   int TotalBinaryIdsSize = 0;
   uint32_t I;
   /* Iterate through entries in the program header. */
   for (I = 0; I < ElfHeader->e_phnum; I++) {
     /* Look for the notes segment in program header entries. */
     if (ProgramHeader[I].p_type != PT_NOTE)
       continue;

     /* There can be multiple notes segment, and examine each of them. */
     const ElfW(Nhdr) * Note;
     const ElfW(Nhdr) * NotesEnd;
     /*
      * When examining notes in file, use p_offset, which is the offset within
      * the elf file, to find the start of notes.
      */
     if (ProgramHeader[I].p_memsz == 0 ||
         ProgramHeader[I].p_memsz == ProgramHeader[I].p_filesz) {
       Note = (const ElfW(Nhdr) *)((uintptr_t)ElfHeader +
                                   ProgramHeader[I].p_offset);
       NotesEnd = (const ElfW(Nhdr) *)((const char *)(Note) +
                                       ProgramHeader[I].p_filesz);
     } else {
       /*
        * When examining notes in memory, use p_vaddr, which is the address of
        * section after loaded to memory, to find the start of notes.
        */
       Note =
           (const ElfW(Nhdr) *)((uintptr_t)ElfHeader + ProgramHeader[I].p_vaddr);
       NotesEnd =
           (const ElfW(Nhdr) *)((const char *)(Note) + ProgramHeader[I].p_memsz);
     }

     int BinaryIdsSize = WriteBinaryIds(Writer, Note, NotesEnd);
     if (TotalBinaryIdsSize == -1)
       return -1;

     TotalBinaryIdsSize += BinaryIdsSize;
   }

   return TotalBinaryIdsSize;
 }
 #else /* !NT_GNU_BUILD_ID */
 /*
  * Fallback implementation for targets that don't support the GNU
  * extensions NT_GNU_BUILD_ID and __ehdr_start.
  */
 COMPILER_RT_VISIBILITY int __llvm_write_binary_ids(ProfDataWriter *Writer) {
   return 0;
 }
 #endif

 #if defined(_AIX)
 // Empty stubs to allow linking object files using the registration-based scheme
 COMPILER_RT_VISIBILITY
 void __llvm_profile_register_function(void *Data_) {}

 COMPILER_RT_VISIBILITY
 void __llvm_profile_register_names_function(void *NamesStart,
                                             uint64_t NamesSize) {}

 // The __start_SECNAME and __stop_SECNAME symbols (for SECNAME \in
 // {"__llvm_prf_cnts", "__llvm_prf_data", "__llvm_prf_name", "__llvm_prf_vnds"})
 // are always live when linking on AIX, regardless if the .o's being linked
 // reference symbols from the profile library (for example when no files were
 // compiled with -fprofile-generate). That's because these symbols are kept
 // alive through references in constructor functions that are always live in the
 // default linking model on AIX (-bcdtors:all). The __start_SECNAME and
 // __stop_SECNAME symbols are only resolved by the linker when the SECNAME
 // section exists. So for the scenario where the user objects have no such
 // section (i.e. when they are compiled with -fno-profile-generate), we always
 // define these zero length variables in each of the above 4 sections.
 COMPILER_RT_VISIBILITY int dummy_cnts[0] COMPILER_RT_SECTION(
     COMPILER_RT_SEG INSTR_PROF_CNTS_SECT_NAME);
 COMPILER_RT_VISIBILITY int dummy_data[0] COMPILER_RT_SECTION(
     COMPILER_RT_SEG INSTR_PROF_DATA_SECT_NAME);
 COMPILER_RT_VISIBILITY const int dummy_name[0] COMPILER_RT_SECTION(
     COMPILER_RT_SEG INSTR_PROF_NAME_SECT_NAME);
 COMPILER_RT_VISIBILITY int dummy_vnds[0] COMPILER_RT_SECTION(
     COMPILER_RT_SEG INSTR_PROF_VNODES_SECT_NAME);

 // Create a fake reference to avoid GC'ing of the dummy variables by the linker.
 // Ideally, we create a ".ref" of each variable inside the function
 // __llvm_profile_begin_counters(), but there's no source level construct
 // that allows us to generate that.
 __attribute__((destructor)) void keep() {
   int volatile use = &dummy_cnts < &dummy_data && &dummy_name < &dummy_vnds;
   (void)use;
 }
 #endif

 #endif
	/===- InstrProfilingPlatformLinux.c - Profile data Linux platform ------===\
	\|*
	\|* Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
	\|* See https://llvm.org/LICENSE.txt for license information.
	\|* SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
	\|*
	\===----------------------------------------------------------------------===/

	#if defined(__linux__) \|\| defined(__FreeBSD__) \|\| defined(__Fuchsia__) \|\| \
	(defined(__sun__) && defined(__svr4__)) \|\| defined(__NetBSD__) \|\| \
	defined(_AIX)

	#if !defined(_AIX)
	#include <elf.h>
	#include <link.h>
	#endif
	#include <stdlib.h>
	#include <string.h>

	#include "InstrProfiling.h"
	#include "InstrProfilingInternal.h"

	#if defined(__FreeBSD__) && !defined(ElfW)
	/*
	* FreeBSD's elf.h and link.h headers do not define the ElfW(type) macro yet.
	* If this is added to all supported FreeBSD versions in the future, this
	* compatibility macro can be removed.
	*/
	#define ElfW(type) __ElfN(type)
	#endif

	#define PROF_DATA_START INSTR_PROF_SECT_START(INSTR_PROF_DATA_COMMON)
	#define PROF_DATA_STOP INSTR_PROF_SECT_STOP(INSTR_PROF_DATA_COMMON)
	#define PROF_NAME_START INSTR_PROF_SECT_START(INSTR_PROF_NAME_COMMON)
	#define PROF_NAME_STOP INSTR_PROF_SECT_STOP(INSTR_PROF_NAME_COMMON)
	#define PROF_CNTS_START INSTR_PROF_SECT_START(INSTR_PROF_CNTS_COMMON)
	#define PROF_CNTS_STOP INSTR_PROF_SECT_STOP(INSTR_PROF_CNTS_COMMON)
	#define PROF_ORDERFILE_START INSTR_PROF_SECT_START(INSTR_PROF_ORDERFILE_COMMON)
	#define PROF_VNODES_START INSTR_PROF_SECT_START(INSTR_PROF_VNODES_COMMON)
	#define PROF_VNODES_STOP INSTR_PROF_SECT_STOP(INSTR_PROF_VNODES_COMMON)

	/* Declare section start and stop symbols for various sections
	* generated by compiler instrumentation.
	*/
	extern __llvm_profile_data PROF_DATA_START COMPILER_RT_VISIBILITY
	COMPILER_RT_WEAK;
	extern __llvm_profile_data PROF_DATA_STOP COMPILER_RT_VISIBILITY
	COMPILER_RT_WEAK;
	extern char PROF_CNTS_START COMPILER_RT_VISIBILITY COMPILER_RT_WEAK;
	extern char PROF_CNTS_STOP COMPILER_RT_VISIBILITY COMPILER_RT_WEAK;
	extern uint32_t PROF_ORDERFILE_START COMPILER_RT_VISIBILITY COMPILER_RT_WEAK;
	extern char PROF_NAME_START COMPILER_RT_VISIBILITY COMPILER_RT_WEAK;
	extern char PROF_NAME_STOP COMPILER_RT_VISIBILITY COMPILER_RT_WEAK;
	extern ValueProfNode PROF_VNODES_START COMPILER_RT_VISIBILITY COMPILER_RT_WEAK;
	extern ValueProfNode PROF_VNODES_STOP COMPILER_RT_VISIBILITY COMPILER_RT_WEAK;

	COMPILER_RT_VISIBILITY const __llvm_profile_data *
	__llvm_profile_begin_data(void) {
	return &PROF_DATA_START;
	}
	COMPILER_RT_VISIBILITY const __llvm_profile_data *
	__llvm_profile_end_data(void) {
	return &PROF_DATA_STOP;
	}
	COMPILER_RT_VISIBILITY const char *__llvm_profile_begin_names(void) {
	return &PROF_NAME_START;
	}
	COMPILER_RT_VISIBILITY const char *__llvm_profile_end_names(void) {
	return &PROF_NAME_STOP;
	}
	COMPILER_RT_VISIBILITY char *__llvm_profile_begin_counters(void) {
	return &PROF_CNTS_START;
	}
	COMPILER_RT_VISIBILITY char *__llvm_profile_end_counters(void) {
	return &PROF_CNTS_STOP;
	}
	COMPILER_RT_VISIBILITY uint32_t *__llvm_profile_begin_orderfile(void) {
	return &PROF_ORDERFILE_START;
	}

	COMPILER_RT_VISIBILITY ValueProfNode *
	__llvm_profile_begin_vnodes(void) {
	return &PROF_VNODES_START;
	}
	COMPILER_RT_VISIBILITY ValueProfNode *__llvm_profile_end_vnodes(void) {
	return &PROF_VNODES_STOP;
	}
	COMPILER_RT_VISIBILITY ValueProfNode *CurrentVNode = &PROF_VNODES_START;
	COMPILER_RT_VISIBILITY ValueProfNode *EndVNode = &PROF_VNODES_STOP;

	#ifdef NT_GNU_BUILD_ID
	static size_t RoundUp(size_t size, size_t align) {
	return (size + align - 1) & ~(align - 1);
	}

	/*
	* Write binary id length and then its data, because binary id does not
	* have a fixed length.
	*/
	static int WriteOneBinaryId(ProfDataWriter *Writer, uint64_t BinaryIdLen,
	const uint8_t *BinaryIdData,
	uint64_t BinaryIdPadding) {
	ProfDataIOVec BinaryIdIOVec[] = {
	{&BinaryIdLen, sizeof(uint64_t), 1, 0},
	{BinaryIdData, sizeof(uint8_t), BinaryIdLen, 0},
	{NULL, sizeof(uint8_t), BinaryIdPadding, 1},
	};
	if (Writer->Write(Writer, BinaryIdIOVec,
	sizeof(BinaryIdIOVec) / sizeof(*BinaryIdIOVec)))
	return -1;

	/* Successfully wrote binary id, report success. */
	return 0;
	}

	/*
	* Look for the note that has the name "GNU\0" and type NT_GNU_BUILD_ID
	* that contains build id. If build id exists, write binary id.
	*
	* Each note in notes section starts with a struct which includes
	* n_namesz, n_descsz, and n_type members. It is followed by the name
	* (whose length is defined in n_namesz) and then by the descriptor
	* (whose length is defined in n_descsz).
	*
	* Note sections like .note.ABI-tag and .note.gnu.build-id are aligned
	* to 4 bytes, so round n_namesz and n_descsz to the nearest 4 bytes.
	*/
	static int WriteBinaryIdForNote(ProfDataWriter *Writer,
	const ElfW(Nhdr) * Note) {
	int BinaryIdSize = 0;
	const char NoteName = (const char )Note + sizeof(ElfW(Nhdr));
	if (Note->n_type == NT_GNU_BUILD_ID && Note->n_namesz == 4 &&
	memcmp(NoteName, "GNU\0", 4) == 0) {
	uint64_t BinaryIdLen = Note->n_descsz;
	const uint8_t *BinaryIdData =
	(const uint8_t *)(NoteName + RoundUp(Note->n_namesz, 4));
	uint8_t BinaryIdPadding = __llvm_profile_get_num_padding_bytes(BinaryIdLen);
	if (Writer != NULL && WriteOneBinaryId(Writer, BinaryIdLen, BinaryIdData,
	BinaryIdPadding) == -1)
	return -1;

	BinaryIdSize = sizeof(BinaryIdLen) + BinaryIdLen + BinaryIdPadding;
	}

	return BinaryIdSize;
	}

	/*
	* Helper function that iterates through notes section and find build ids.
	* If writer is given, write binary ids into profiles.
	* If an error happens while writing, return -1.
	*/
	static int WriteBinaryIds(ProfDataWriter Writer, const ElfW(Nhdr) Note,
	const ElfW(Nhdr) * NotesEnd) {
	int BinaryIdsSize = 0;
	while (Note < NotesEnd) {
	int OneBinaryIdSize = WriteBinaryIdForNote(Writer, Note);
	if (OneBinaryIdSize == -1)
	return -1;
	BinaryIdsSize += OneBinaryIdSize;

	/* Calculate the offset of the next note in notes section. */
	size_t NoteOffset = sizeof(ElfW(Nhdr)) + RoundUp(Note->n_namesz, 4) +
	RoundUp(Note->n_descsz, 4);
	Note = (const ElfW(Nhdr) )((const char )(Note) + NoteOffset);
	}

	return BinaryIdsSize;
	}

	/*
	* Write binary ids into profiles if writer is given.
	* Return the total size of binary ids.
	* If an error happens while writing, return -1.
	*/
	COMPILER_RT_VISIBILITY int __llvm_write_binary_ids(ProfDataWriter *Writer) {
	extern const ElfW(Ehdr) __ehdr_start __attribute__((visibility("hidden")));
	const ElfW(Ehdr) *ElfHeader = &__ehdr_start;
	const ElfW(Phdr) *ProgramHeader =
	(const ElfW(Phdr) *)((uintptr_t)ElfHeader + ElfHeader->e_phoff);

	int TotalBinaryIdsSize = 0;
	uint32_t I;
	/* Iterate through entries in the program header. */
	for (I = 0; I < ElfHeader->e_phnum; I++) {
	/* Look for the notes segment in program header entries. */
	if (ProgramHeader[I].p_type != PT_NOTE)
	continue;

	/* There can be multiple notes segment, and examine each of them. */
	const ElfW(Nhdr) * Note;
	const ElfW(Nhdr) * NotesEnd;
	/*
	* When examining notes in file, use p_offset, which is the offset within
	* the elf file, to find the start of notes.
	*/
	if (ProgramHeader[I].p_memsz == 0 \|\|
	ProgramHeader[I].p_memsz == ProgramHeader[I].p_filesz) {
	Note = (const ElfW(Nhdr) *)((uintptr_t)ElfHeader +
	ProgramHeader[I].p_offset);
	NotesEnd = (const ElfW(Nhdr) )((const char )(Note) +
	ProgramHeader[I].p_filesz);
	} else {
	/*
	* When examining notes in memory, use p_vaddr, which is the address of
	* section after loaded to memory, to find the start of notes.
	*/
	Note =
	(const ElfW(Nhdr) *)((uintptr_t)ElfHeader + ProgramHeader[I].p_vaddr);
	NotesEnd =
	(const ElfW(Nhdr) )((const char )(Note) + ProgramHeader[I].p_memsz);
	}

	int BinaryIdsSize = WriteBinaryIds(Writer, Note, NotesEnd);
	if (TotalBinaryIdsSize == -1)
	return -1;

	TotalBinaryIdsSize += BinaryIdsSize;
	}

	return TotalBinaryIdsSize;
	}
	#else /* !NT_GNU_BUILD_ID */
	/*
	* Fallback implementation for targets that don't support the GNU
	* extensions NT_GNU_BUILD_ID and __ehdr_start.
	*/
	COMPILER_RT_VISIBILITY int __llvm_write_binary_ids(ProfDataWriter *Writer) {
	return 0;
	}
	#endif

	#if defined(_AIX)
	// Empty stubs to allow linking object files using the registration-based scheme
	COMPILER_RT_VISIBILITY
	void __llvm_profile_register_function(void *Data_) {}

	COMPILER_RT_VISIBILITY
	void __llvm_profile_register_names_function(void *NamesStart,
	uint64_t NamesSize) {}

	// The __start_SECNAME and __stop_SECNAME symbols (for SECNAME \in
	// {"__llvm_prf_cnts", "__llvm_prf_data", "__llvm_prf_name", "__llvm_prf_vnds"})
	// are always live when linking on AIX, regardless if the .o's being linked
	// reference symbols from the profile library (for example when no files were
	// compiled with -fprofile-generate). That's because these symbols are kept
	// alive through references in constructor functions that are always live in the
	// default linking model on AIX (-bcdtors:all). The __start_SECNAME and
	// __stop_SECNAME symbols are only resolved by the linker when the SECNAME
	// section exists. So for the scenario where the user objects have no such
	// section (i.e. when they are compiled with -fno-profile-generate), we always
	// define these zero length variables in each of the above 4 sections.
	COMPILER_RT_VISIBILITY int dummy_cnts[0] COMPILER_RT_SECTION(
	COMPILER_RT_SEG INSTR_PROF_CNTS_SECT_NAME);
	COMPILER_RT_VISIBILITY int dummy_data[0] COMPILER_RT_SECTION(
	COMPILER_RT_SEG INSTR_PROF_DATA_SECT_NAME);
	COMPILER_RT_VISIBILITY const int dummy_name[0] COMPILER_RT_SECTION(
	COMPILER_RT_SEG INSTR_PROF_NAME_SECT_NAME);
	COMPILER_RT_VISIBILITY int dummy_vnds[0] COMPILER_RT_SECTION(
	COMPILER_RT_SEG INSTR_PROF_VNODES_SECT_NAME);

	// Create a fake reference to avoid GC'ing of the dummy variables by the linker.
	// Ideally, we create a ".ref" of each variable inside the function
	// __llvm_profile_begin_counters(), but there's no source level construct
	// that allows us to generate that.
	__attribute__((destructor)) void keep() {
	int volatile use = &dummy_cnts < &dummy_data && &dummy_name < &dummy_vnds;
	(void)use;
	}
	#endif

	#endif