driver: Fix up -freport-bug for ASLR [PR119727]

With --enable-host-pie -freport-bug almost never prepares preprocessed
source and instead emits
The bug is not reproducible, so it is likely a hardware or OS problem.
message even for bogus which are 100% reproducible.
The way -freport-bug works is that it reruns it 3 times, capturing stdout
and stderr from each and then tries to compare the outputs in between
different runs.
The libbacktrace emitted hexadecimal addresses at the start of the lines
can differ between runs due to ASLR, either of the PIE executable, or
even if not PIE if there is some frame with e.g. libc function (say
crash in strlen/memcpy etc.).

The following patch fixes it by ignoring such differences at the start of
the lines.

2025-04-12  Jakub Jelinek  <jakub@redhat.com>

	PR driver/119727
	* gcc.cc (files_equal_p): Rewritten using fopen/fgets/fclose instead
	of open/fstat/read/close.  At the start of lines, ignore lowercase
	hexadecimal addresses followed by space.

1 files changed, 38 insertions, 35 deletions

diff --git a/gcc/gcc.cc b/gcc/gcc.cc
index aac33e9..9064671 100644
--- a/gcc/gcc.cc
+++ b/gcc/gcc.cc
@@ -7744,55 +7744,58 @@ print_configuration (FILE *file)
 
 #define RETRY_ICE_ATTEMPTS 3
 
-/* Returns true if FILE1 and FILE2 contain equivalent data, 0 otherwise.  */
+/* Returns true if FILE1 and FILE2 contain equivalent data, 0 otherwise.
+   If lines start with 0x followed by 1-16 lowercase hexadecimal digits
+   followed by a space, ignore anything before that space.  These are
+   typically function addresses from libbacktrace and those can differ
+   due to ASLR.  */
 
 static bool
 files_equal_p (char *file1, char *file2)
 {
-  struct stat st1, st2;
-  off_t n, len;
-  int fd1, fd2;
-  const int bufsize = 8192;
-  char *buf = XNEWVEC (char, bufsize);
+  FILE *f1 = fopen (file1, "rb");
+  FILE *f2 = fopen (file2, "rb");
+  char line1[256], line2[256];
 
-  fd1 = open (file1, O_RDONLY);
-  fd2 = open (file2, O_RDONLY);
-
-  if (fd1 < 0 || fd2 < 0)
-    goto error;
-
-  if (fstat (fd1, &st1) < 0 || fstat (fd2, &st2) < 0)
-    goto error;
-
-  if (st1.st_size != st2.st_size)
-    goto error;
-
-  for (n = st1.st_size; n; n -= len)
+  bool line_start = true;
+  while (fgets (line1, sizeof (line1), f1))
     {
-      len = n;
-      if ((int) len > bufsize / 2)
-	len = bufsize / 2;
-
-      if (read (fd1, buf, len) != (int) len
-	  || read (fd2, buf + bufsize / 2, len) != (int) len)
+      if (!fgets (line2, sizeof (line2), f2))
+	goto error;
+      char *p1 = line1, *p2 = line2;
+      if (line_start
+	  && line1[0] == '0'
+	  && line1[1] == 'x'
+	  && line2[0] == '0'
+	  && line2[1] == 'x')
 	{
-	  goto error;
+	  int i, j;
+	  for (i = 0; i < 16; ++i)
+	    if (!ISXDIGIT (line1[2 + i]) || ISUPPER (line1[2 + i]))
+	      break;
+	  for (j = 0; j < 16; ++j)
+	    if (!ISXDIGIT (line2[2 + j]) || ISUPPER (line2[2 + j]))
+	      break;
+	  if (i && line1[2 + i] == ' ' && j && line2[2 + j] == ' ')
+	    {
+	      p1 = line1 + i + 3;
+	      p2 = line2 + j + 3;
+	    }
 	}
-
-      if (memcmp (buf, buf + bufsize / 2, len) != 0)
+      if (strcmp (p1, p2) != 0)
 	goto error;
+      line_start = strchr (line1, '\n') != NULL;
     }
+  if (fgets (line2, sizeof (line2), f2))
+    goto error;
 
-  free (buf);
-  close (fd1);
-  close (fd2);
-
+  fclose (f1);
+  fclose (f2);
   return 1;
 
 error:
-  free (buf);
-  close (fd1);
-  close (fd2);
+  fclose (f1);
+  fclose (f2);
   return 0;
 }