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

Pedro Alves
2014-07-15T13:01:36Z

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