[PATCH 1/2] Fix write endianness/size problem for fast tracepoint enabled flag

Simon Marchi
2016-03-30T15:17:18Z

From: Par Olsson <par.olsson@windriver.com>

I am sending this fix on behalf of Par Olsson, as a follow-up of this
one:

https://www.sourceware.org/ml/gdb-patches/2015-10/msg00196.html

This problem is exposed when enabling/disabling fast tracepoints on big
endian machines. The flag is defined as an int8_t, but is written from
gdbserver as an integer (usually 32 bits). When the agent code reads it
as an int8_t, it only considers the most significant byte, which is
always 0.

Also, we were writing 32 bits in an 8 bits field, so the write would
overflow, but since the following bytes are padding (the next field is
an uint64_t), it luckily didn't cause any issue on little endian
systems.

The fix was originally tested on ARM big endian systems, but I don't
have access to such a system. However, thanks to Marcin's PowerPC fast
tracepoint patches and gcc110 (big endian Power7) on the gcc compile
farm, I was able to reproduce the problem, test the fix and write a
test (the following patch).

gdb/gdbserver/ChangeLog:

YYYY-MM-DD Par Olsson <par.olsson@windriver.com>

* tracepoint.c (write_inferior_int8): New function.
(cmd_qtenable_disable): Write enable flag using
write_inferior_int8.
---
gdb/gdbserver/tracepoint.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/gdb/gdbserver/tracepoint.c b/gdb/gdbserver/tracepoint.c
index 7c20612..3e0d57a 100644
--- a/gdb/gdbserver/tracepoint.c
+++ b/gdb/gdbserver/tracepoint.c
@@ -449,6 +449,12 @@ write_inferior_integer (CORE_ADDR symaddr, int val)
}

static int
+write_inferior_int8 (CORE_ADDR symaddr, int8_t val)
+{
+ return write_inferior_memory (symaddr, (unsigned char *) &val, sizeof (val));
+}
+
+static int
write_inferior_uinteger (CORE_ADDR symaddr, unsigned int val)
{
return write_inferior_memory (symaddr, (unsigned char *) &val, sizeof (val));
@@ -2784,7 +2790,7 @@ cmd_qtenable_disable (char *own_buf, int enable)
return;
}

- ret = write_inferior_integer (obj_addr, enable);
+ ret = write_inferior_int8 (obj_addr, enable);
done_accessing_memory ();

if (ret)
--
2.8.0