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authorPedro Alves <pedro@palves.net>2022-03-31 22:04:42 +0100
committerPedro Alves <pedro@palves.net>2022-04-14 20:22:42 +0100
commit366e3746c572c2c78454761e62fa9181cba413ca (patch)
tree732c601e940cd5b648b4e1ccf2f0b38443ee0c1d /gdbserver/target.cc
parent330d63093c562a4b221835832c5e4f767dc623c3 (diff)
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gdbserver: special case target_write_memory len==0
The next patch in this series adds a common helper routine for both memory reads and writes, like this: static int proc_xfer_memory (CORE_ADDR memaddr, unsigned char *readbuf, const gdb_byte *writebuf, int len) { gdb_assert ((readbuf == nullptr) != (writebuf == nullptr)); ... } int linux_process_target::read_memory (CORE_ADDR memaddr, unsigned char *myaddr, int len) { return proc_xfer_memory (memaddr, myaddr, nullptr, len); } linux_process_target::write_memory (CORE_ADDR memaddr, const unsigned char *myaddr, int len) { return proc_xfer_memory (memaddr, nullptr, myaddr, len); } Surprisingly, the assertion fails. That happens because it can happen that target_write_memory is called with LEN==0, due to this in gdb/remote.c: /* Determine whether the remote target supports binary downloading. This is accomplished by sending a no-op memory write of zero length to the target at the specified address. (...) */ void remote_target::check_binary_download (CORE_ADDR addr) { ... p = rs->buf.data (); *p++ = 'X'; p += hexnumstr (p, (ULONGEST) addr); *p++ = ','; p += hexnumstr (p, (ULONGEST) 0); *p++ = ':'; *p = '\0'; In this scenario, in gdbserver's target_write_memory, the "myaddr" argument of the_target->write_memory is passed the data() of a local gdb::byte_vector (which is a specialized std::vector). It's valid for std::vector::data() to return NULL when the vector is empty. This commit adds an early return to target_write_memory to avoid target backends having to care about this. For good measure, do the same on the read side, in read_inferior_memory. Change-Id: Iac8f04fcf99014c624ef4036bd318ca1771ad491
Diffstat (limited to 'gdbserver/target.cc')
-rw-r--r--gdbserver/target.cc17
1 files changed, 15 insertions, 2 deletions
diff --git a/gdbserver/target.cc b/gdbserver/target.cc
index 5009146..e9d1e1a 100644
--- a/gdbserver/target.cc
+++ b/gdbserver/target.cc
@@ -124,8 +124,14 @@ done_accessing_memory (void)
int
read_inferior_memory (CORE_ADDR memaddr, unsigned char *myaddr, int len)
{
- int res;
- res = the_target->read_memory (memaddr, myaddr, len);
+ /* At the time of writing, GDB only sends write packets with LEN==0,
+ not read packets (see comment in target_write_memory), but it
+ doesn't hurt to prevent problems if it ever does, or we're
+ connected to some client other than GDB that does. */
+ if (len == 0)
+ return 0;
+
+ int res = the_target->read_memory (memaddr, myaddr, len);
check_mem_read (memaddr, myaddr, len);
return res;
}
@@ -152,6 +158,13 @@ int
target_write_memory (CORE_ADDR memaddr, const unsigned char *myaddr,
ssize_t len)
{
+ /* GDB may send X packets with LEN==0, for probing packet support.
+ If we let such a request go through, then buffer.data() below may
+ return NULL, which may confuse target implementations. Handle it
+ here to avoid lower levels having to care about this case. */
+ if (len == 0)
+ return 0;
+
/* Make a copy of the data because check_mem_write may need to
update it. */
gdb::byte_vector buffer (myaddr, myaddr + len);