[PATCH] D49132: Fix gcov profiling on big-endian machines

[Ulrich Weigand via Phabricator via llvm-commits]

uweigand created this revision.
uweigand added reviewers: marco-c, syzaara, sfertile, davidxl.
Herald added a subscriber: llvm-commits.

The compiler-rt library support for gcov is currently only working correctly on little-endian systems.

Two separate fixes are required to handle big-endian systems as well:

- 64-bit counter values are stored in a mixed-endian format in the gcov files: a 32-bit low-part followed by a 32-bit high part.  Note that this is already implemented correctly on the LLVM side, see GCOVBuffer::readInt64.
- The tag values (e.g. arcs tag, object summary tag, ...) are aways written as the same sequence of bytes independent of byte order.  But when *reading* them back in, the code reads them as 32-bit values in host byte order.  For the comparisons to work correctly, this should instead always read them as little-endian values.


Repository:
  rL LLVM

https://reviews.llvm.org/D49132

Files:
  lib/profile/GCDAProfiling.c


Index: lib/profile/GCDAProfiling.c
===================================================================
--- lib/profile/GCDAProfiling.c
+++ lib/profile/GCDAProfiling.c
@@ -178,7 +178,12 @@
 }
 
 static void write_64bit_value(uint64_t i) {
-  write_bytes((char*)&i, 8);
+  // GCOV uses a lo-/hi-word format even on big-endian systems.
+  // See also GCOVBuffer::readInt64 in LLVM.
+  uint32_t lo = (uint32_t) i;
+  uint32_t hi = (uint32_t) (i >> 32);
+  write_32bit_value(lo);
+  write_32bit_value(hi);
 }
 
 static uint32_t length_of_string(const char *s) {
@@ -203,17 +208,25 @@
   return val;
 }
 
-static uint64_t read_64bit_value() {
-  uint64_t val;
+static uint32_t read_le_32bit_value() {
+  uint32_t val = 0;
 
   if (new_file)
-    return (uint64_t)-1;
+    return (uint32_t)-1;
 
-  val = *(uint64_t*)&write_buffer[cur_pos];
-  cur_pos += 8;
+  for (int i = 0; i < 4; i++)
+    val |= write_buffer[cur_pos++] << (8*i);
   return val;
 }
 
+static uint64_t read_64bit_value() {
+  // GCOV uses a lo-/hi-word format even on big-endian systems.
+  // See also GCOVBuffer::readInt64 in LLVM.
+  uint32_t lo = read_32bit_value();
+  uint32_t hi = read_32bit_value();
+  return ((uint64_t)hi << 32) | ((uint64_t)lo);
+}
+
 static char *mangle_filename(const char *orig_filename) {
   char *new_filename;
   size_t prefix_len;
@@ -400,7 +413,7 @@
 
   if (!output_file) return;
 
-  val = read_32bit_value();
+  val = read_le_32bit_value();
 
   if (val != (uint32_t)-1) {
     /* There are counters present in the file. Merge them. */
@@ -454,7 +467,7 @@
 
   if (!output_file) return;
 
-  val = read_32bit_value();
+  val = read_le_32bit_value();
 
   if (val != (uint32_t)-1) {
     /* There are counters present in the file. Merge them. */


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