Re: [PATCH] Tweak gdb.trace/tfile.c for thumb mode

[Pedro Alves <palves at redhat dot com>]

On 07/10/2014 02:26 AM, Yao Qi wrote:
> On 07/09/2014 10:52 PM, Pedro Alves wrote:
>> #if defined(__thumb__) || defined(__thumb2__)
>>   /* Although Thumb functions are two-byte aligned, function
>>      pointers have the Thumb bit set.  Clear it.  */
>>   func_addr &= ~1;
>> #endif
>>
>> (This bit is widely known as the "Thumb bit", so call it that,
>> and remove a few "the"'s that sound odd to me, and say
>> "two-byte aligned".)
> 
> I often associate "Thumb bit" with the bit in CPSR.  Look into
> arm-tdep.c and arm-linux-tdep.c, "Thumb bit" is used for both cases
> (LSB of function address and the bit in CPSR).  It shouldn't cause any
> confusion.
> 
> Patch is updated as you suggested and pushed in.
> 

Thanks.  The use of 'long' for holding an address made me take
another look.  I thought the test must be failing to build on
Win64 due to warnings, but it turns out warnings are being
suppressed currently.  I took a stab at fixing it.  While doing
that I noticed that write_error_trace_file needs the Thumb
treatment too?

WDYT of the patch below?  I don't think we need to worry about
targets that don't have stdint.h in this test and at this
day and age.

8<-------------------------------

>From fbd5a81a0cb775c3bc7798a0d2510321c41bcc53 Mon Sep 17 00:00:00 2001
From: Pedro Alves <palves@redhat.com>
Date: Tue, 15 Jul 2014 13:44:16 +0100
Subject: [PATCH] gdb.trace/tfile.c: Remove Thumb bit in one more more, general
 cleanup

I noticed that the existing code casts a function's address to 'long',
but that doesn't work correctly on some ABIs, like Win64, where long
is 32-bit and while pointers are 64-bit:

  func_addr = (long) &write_basic_trace_file;

Fixing that showed there's actually another place in the file that
writes a function address to file, and therefore should clear the
Thumb bit.  This commit adds a macro+function pair to centralize the
Thumb bit handling, and uses it in both places.

The rest is just enough changes to make the file build without
warnings with "-Wall -Wextra" with x86_64-w64-mingw32-gcc and
i686-w64-mingw32-gcc cross compilers, and with -m32/-m64 on x86_64
GNU/Linux.  Currently with x86_64-w64-mingw32-gcc we get:

  $ x86_64-w64-mingw32-gcc tfile.c  -Wall -DTFILE_DIR=\"\"
  tfile.c: In function 'start_trace_file':
  tfile.c:51:23: error: 'S_IRGRP' undeclared (first use in this function)
	 S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH);
			 ^
  tfile.c:51:23: note: each undeclared identifier is reported only once for each function it appears in
  tfile.c:51:31: error: 'S_IROTH' undeclared (first use in this function)
	 S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH);
				 ^
  tfile.c: In function 'add_memory_block':
  tfile.c:79:10: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
     ll_x = (unsigned long) addr;
	    ^
  tfile.c: In function 'write_basic_trace_file':
  tfile.c:113:15: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
     func_addr = (long) &write_basic_trace_file;
		 ^
  tfile.c:137:3: warning: passing argument 1 of 'add_memory_block' from incompatible pointer type [enabled by default]
     add_memory_block (&testglob, sizeof (testglob));
     ^
  tfile.c:72:1: note: expected 'char *' but argument is of type 'int *'
   add_memory_block (char *addr, int size)
   ^
  tfile.c:139:3: warning: passing argument 1 of 'add_memory_block' from incompatible pointer type [enabled by default]
     add_memory_block (&testglob2, 1);
     ^
  tfile.c:72:1: note: expected 'char *' but argument is of type 'int *'
   add_memory_block (char *addr, int size)
   ^
  tfile.c: In function 'write_error_trace_file':
  tfile.c:185:3: warning: implicit declaration of function 'alloca' [-Wimplicit-function-declaration]
     char *hex = alloca (len * 2 + 1);
     ^
  tfile.c:185:15: warning: incompatible implicit declaration of built-in function 'alloca' [enabled by default]
     char *hex = alloca (len * 2 + 1);
		 ^
  tfile.c:211:6: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
	(long) &write_basic_trace_file);
      ^

The test still passes for me on x86_64 Fedora 20.

gdb/testsuite/
2014-07-15  Pedro Alves  <palves@redhat.com>

	* gdb.trace/tfile.c: Include unistd.h and stdint.h.
	(start_trace_file): Guard S_IRGRP and S_IROTH uses behind #ifdef.
	(tfile_write_64, tfile_write_16, tfile_write_8, tfile_write_addr)
	(tfile_write_buf): New functions.
	(add_memory_block): Rewrite using the above.
	(adjust_function_address): New function.
	(FUNCTION_ADDRESS): New macro.
	(write_basic_trace_file): Remove short_x local, and use
	tfile_write_16. Change type of func_addr local to unsigned long
	long.  Use FUNCTION_ADDRESS instead of handling the Thumb bit
	here.  Cast argument of add_memory_block to char pointer.
	(write_error_trace_file): Avoid alloca.  Use FUNCTION_ADDRESS.
	(main): Remove parameters.
	* gdb.trace/tfile.exp: Remove nowarnings.
---
 gdb/testsuite/gdb.trace/tfile.c   | 113 ++++++++++++++++++++++++++------------
 gdb/testsuite/gdb.trace/tfile.exp |   2 +-
 2 files changed, 80 insertions(+), 35 deletions(-)

diff --git a/gdb/testsuite/gdb.trace/tfile.c b/gdb/testsuite/gdb.trace/tfile.c
index bc25b80..9702afa 100644
--- a/gdb/testsuite/gdb.trace/tfile.c
+++ b/gdb/testsuite/gdb.trace/tfile.c
@@ -20,9 +20,11 @@
    GDB.  */
 
 #include <stdio.h>
+#include <unistd.h>
 #include <string.h>
 #include <fcntl.h>
 #include <sys/stat.h>
+#include <stdint.h>
 
 char spbuf[200];
 
@@ -46,9 +48,17 @@ int
 start_trace_file (char *filename)
 {
   int fd;
+  mode_t mode = S_IRUSR | S_IWUSR;
 
-  fd = open (filename, O_WRONLY|O_CREAT|O_APPEND,
-	     S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH);
+#ifdef S_IRGRP
+  mode |= S_IRGRP;
+#endif
+
+#ifdef S_IROTH
+  mode |= S_IROTH;
+#endif
+
+  fd = open (filename, O_WRONLY|O_CREAT|O_APPEND, mode);
 
   if (fd < 0)
     return fd;
@@ -67,31 +77,73 @@ finish_trace_file (int fd)
   close (fd);
 }
 
+static void
+tfile_write_64 (uint64_t value)
+{
+  memcpy (trptr, &value, sizeof (uint64_t));
+  trptr += sizeof (uint64_t);
+}
 
-void
-add_memory_block (char *addr, int size)
+static void
+tfile_write_16 (uint16_t value)
+{
+  memcpy (trptr, &value, sizeof (uint16_t));
+  trptr += sizeof (uint16_t);
+}
+
+static void
+tfile_write_8 (uint8_t value)
+{
+  memcpy (trptr, &value, sizeof (uint8_t));
+  trptr += sizeof (uint8_t);
+}
+
+static void
+tfile_write_addr (char *addr)
+{
+  tfile_write_64 ((uint64_t) (uintptr_t) addr);
+}
+
+static void
+tfile_write_buf (const void *addr, size_t size)
 {
-  short short_x;
-  unsigned long long ll_x;
-
-  *((char *) trptr) = 'M';
-  trptr += 1;
-  ll_x = (unsigned long) addr;
-  memcpy (trptr, &ll_x, sizeof (unsigned long long));
-  trptr += sizeof (unsigned long long);
-  short_x = size;
-  memcpy (trptr, &short_x, 2);
-  trptr += 2;
   memcpy (trptr, addr, size);
   trptr += size;
 }
 
 void
+add_memory_block (char *addr, int size)
+{
+  tfile_write_8 ('M');
+  tfile_write_addr (addr);
+  tfile_write_16 (size);
+  tfile_write_buf (addr, size);
+}
+
+/* Adjust a function's address to account for architectural
+   particularities.  */
+
+static uintptr_t
+adjust_function_address (uintptr_t func_addr)
+{
+#if defined(__thumb__) || defined(__thumb2__)
+  /* Although Thumb functions are two-byte aligned, function
+     pointers have the Thumb bit set.  Clear it.  */
+  return func_addr & ~1;
+#else
+  return func_addr;
+#endif
+}
+
+/* Get a function's address as an integer.  */
+
+#define FUNCTION_ADDRESS(FUN) adjust_function_address ((uintptr_t) &FUN)
+
+void
 write_basic_trace_file (void)
 {
   int fd, int_x;
-  short short_x;
-  long func_addr;
+  unsigned long long func_addr;
 
   fd = start_trace_file (TFILE_DIR "tfile-basic.tf");
 
@@ -110,14 +162,9 @@ write_basic_trace_file (void)
   /* Dump tracepoint definitions, in syntax similar to that used
      for reconnection uploads.  */
   /* FIXME need a portable way to print function address in hex */
-  func_addr = (long) &write_basic_trace_file;
-#if defined(__thumb__) || defined(__thumb2__)
-  /* Although Thumb functions are two-byte aligned, function
-     pointers have the Thumb bit set.  Clear it.  */
-  func_addr &= ~1;
-#endif
+  func_addr = FUNCTION_ADDRESS (write_basic_trace_file);
 
-  snprintf (spbuf, sizeof spbuf, "tp T1:%lx:E:0:0\n", func_addr);
+  snprintf (spbuf, sizeof spbuf, "tp T1:%llx:E:0:0\n", func_addr);
   write (fd, spbuf, strlen (spbuf));
   /* (Note that we would only need actions defined if we wanted to
      test tdump.) */
@@ -129,14 +176,13 @@ write_basic_trace_file (void)
   /* (Encapsulate better if we're going to do lots of this; note that
      buffer endianness is the target program's enddianness.) */
   trptr = trbuf;
-  short_x = 1;
-  memcpy (trptr, &short_x, 2);
-  trptr += 2;
+  tfile_write_16 (1);
+
   tfsizeptr = trptr;
   trptr += 4;
-  add_memory_block (&testglob, sizeof (testglob));
+  add_memory_block ((char *) &testglob, sizeof (testglob));
   /* Divide a variable between two separate memory blocks.  */
-  add_memory_block (&testglob2, 1);
+  add_memory_block ((char *) &testglob2, 1);
   add_memory_block (((char*) &testglob2) + 1, sizeof (testglob2) - 1);
   /* Go back and patch in the frame size.  */
   int_x = trptr - tfsizeptr - sizeof (int);
@@ -181,8 +227,8 @@ write_error_trace_file (void)
 {
   int fd;
   const char made_up[] = "made-up error";
+  char hex[(sizeof (made_up) - 1) * 2 + 1];
   int len = sizeof (made_up) - 1;
-  char *hex = alloca (len * 2 + 1);
 
   fd = start_trace_file (TFILE_DIR "tfile-error.tf");
 
@@ -206,9 +252,8 @@ write_error_trace_file (void)
 
   /* Dump tracepoint definitions, in syntax similar to that used
      for reconnection uploads.  */
-  /* FIXME need a portable way to print function address in hex */
-  snprintf (spbuf, sizeof spbuf, "tp T1:%lx:E:0:0\n",
-	    (long) &write_basic_trace_file);
+  snprintf (spbuf, sizeof spbuf, "tp T1:%llx:E:0:0\n",
+	    (unsigned long long) FUNCTION_ADDRESS (write_basic_trace_file));
   write (fd, spbuf, strlen (spbuf));
   /* (Note that we would only need actions defined if we wanted to
      test tdump.) */
@@ -233,7 +278,7 @@ done_making_trace_files (void)
 }
 
 int
-main (int argc, char **argv, char **envp)
+main (void)
 {
   write_basic_trace_file ();
 
diff --git a/gdb/testsuite/gdb.trace/tfile.exp b/gdb/testsuite/gdb.trace/tfile.exp
index d6a60e5..54648b8 100644
--- a/gdb/testsuite/gdb.trace/tfile.exp
+++ b/gdb/testsuite/gdb.trace/tfile.exp
@@ -37,7 +37,7 @@ if {![is_remote host] && ![is_remote target]} {
 standard_testfile
 if { [gdb_compile "$srcdir/$subdir/$srcfile" $binfile \
 	  executable \
-	  [list debug nowarnings \
+	  [list debug \
 	       "additional_flags=-DTFILE_DIR=\"$tfile_dir\""]] \
 	 != "" } {
     untested ${testfile}.exp
-- 
1.9.3