gdbserver: fix memory leak when handling qsupported packet

When building gdbserver with AddressSanitizer, I get this annoying
little leak when gdbserver exits:

==307817==ERROR: LeakSanitizer: detected memory leaks

    Direct leak of 14 byte(s) in 1 object(s) allocated from:
        #0 0x7f7fd4256459 in __interceptor_malloc /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cpp:145
        #1 0x563bef981b80 in xmalloc /home/simark/src/binutils-gdb/gdbserver/../gdb/alloc.c:60
        #2 0x563befb53301 in xstrdup /home/simark/src/binutils-gdb/libiberty/xstrdup.c:34
        #3 0x563bef9d742b in handle_query /home/simark/src/binutils-gdb/gdbserver/server.cc:2286
        #4 0x563bef9ed0b7 in process_serial_event /home/simark/src/binutils-gdb/gdbserver/server.cc:4061
        #5 0x563bef9f1d9e in handle_serial_event(int, void*) /home/simark/src/binutils-gdb/gdbserver/server.cc:4402
        #6 0x563befb0ec65 in handle_file_event /home/simark/src/binutils-gdb/gdbsupport/event-loop.cc:548
        #7 0x563befb0f49f in gdb_wait_for_event /home/simark/src/binutils-gdb/gdbsupport/event-loop.cc:673
        #8 0x563befb0d4a1 in gdb_do_one_event() /home/simark/src/binutils-gdb/gdbsupport/event-loop.cc:215
        #9 0x563bef9e721a in start_event_loop /home/simark/src/binutils-gdb/gdbserver/server.cc:3484
        #10 0x563bef9eb90a in captured_main /home/simark/src/binutils-gdb/gdbserver/server.cc:3875
        #11 0x563bef9ec2c7 in main /home/simark/src/binutils-gdb/gdbserver/server.cc:3961
        #12 0x7f7fd3330001 in __libc_start_main (/usr/lib/libc.so.6+0x27001)

    SUMMARY: AddressSanitizer: 14 byte(s) leaked in 1 allocation(s).

This is due to the handling of unknown qsupported features in
handle_query.  The `qsupported` vector is built, containing all the
feature names received from GDB.  As we iterate on them, when we
encounter unknown ones, we move them at the beginning of the vector, in
preparation of passing this vector of unknown features down to the
target (which may know about them).

When moving these unknown features to other slots in the vector, we
overwrite other pointers without freeing them, which therefore leak.

An easy fix would be to add a `free` when doing the move.  However, I
think this is a good opportunity to sprinkle a bit of automatic memory
management in this code.

So, use a vector of std::string which owns all the entries.  And use a
separate vector (that doesn't own the entries) for the unknown ones,
which is then passed to target_process_qsupported.

Given that the `c_str` method of std::string returns a `const char *`,
it follows that process_stratum_target::process_qsupported must accept a
`const char **` instead of a `char **`.  And while at it, change the
pointer + size paramters to use an array_view instead.

gdbserver/ChangeLog:

	* server.cc (handle_query): Use std::vector of
	std::string for `qsupported` vector.  Use separate
	vector for unknowns.
	* target.h (class process_stratum_target) <process_qsupported>:
	Change parameters to array_view of const char *.
	(target_process_qsupported): Remove `count` parameter.
	* target.cc (process_stratum_target::process_qsupported): Change
	parameters to array_view of const char *.
	* linux-x86-low.cc (class x86_target) <process_qsupported>:
	Likewise.

Change-Id: I97f133825faa6d7abbf83a58504eb0ba77462812

diff --git a/gdbserver/ChangeLog b/gdbserver/ChangeLog
index 4ed5d6101612a086fd3d1bf9ac9efcd5db67a4a7..1ee716f52d7eda530b860e503c6623e3799812fc 100644 (file)
--- a/gdbserver/ChangeLog
+++ b/gdbserver/ChangeLog
@@ -1,3 +1,16 @@
+2020-07-13  Simon Marchi  <simon.marchi@polymtl.ca>
+
+       * server.cc (handle_query): Use std::vector of
+       std::string for `qsupported` vector.  Use separate
+       vector for unknowns.
+       * target.h (class process_stratum_target) <process_qsupported>:
+       Change parameters to array_view of const char *.
+       (target_process_qsupported): Remove `count` parameter.
+       * target.cc (process_stratum_target::process_qsupported): Change
+       parameters to array_view of const char *.
+       * linux-x86-low.cc (class x86_target) <process_qsupported>:
+       Likewise.
+
 2020-06-29  Tom de Vries  <tdevries@suse.de>
 
        * ax.h: Include gdbsupport/debug_agent.h.

diff --git a/gdbserver/linux-x86-low.cc b/gdbserver/linux-x86-low.cc
index 7a65c1d079f86e96d1b0ee3f816e358a0bbdb6f4..37d3626e1f73671f8852ecf4cef1f933823377d0 100644 (file)
--- a/gdbserver/linux-x86-low.cc
+++ b/gdbserver/linux-x86-low.cc
@@ -106,7 +106,7 @@ public:
 
   bool supports_z_point_type (char z_type) override;
 
-  void process_qsupported (char **features, int count) override;
+  void process_qsupported (gdb::array_view<const char * const> features) override;
 
   bool supports_tracepoints () override;
 
@@ -1003,18 +1003,15 @@ x86_target::update_xmltarget ()
    PTRACE_GETREGSET.  */
 
 void
-x86_target::process_qsupported (char **features, int count)
+x86_target::process_qsupported (gdb::array_view<const char * const> features)
 {
-  int i;
-
   /* Return if gdb doesn't support XML.  If gdb sends "xmlRegisters="
      with "i386" in qSupported query, it supports x86 XML target
      descriptions.  */
   use_xml = 0;
-  for (i = 0; i < count; i++)
-    {
-      const char *feature = features[i];
 
+  for (const char *feature : features)
+    {
       if (startswith (feature, "xmlRegisters="))
        {
          char *copy = xstrdup (feature + 13);
@@ -1034,6 +1031,7 @@ x86_target::process_qsupported (char **features, int count)
          free (copy);
        }
     }
+
   update_xmltarget ();
 }
 

diff --git a/gdbserver/server.cc b/gdbserver/server.cc
index 0313d18bb24720c2f8c07046715f19a988540f8e..ab5363eb03286347c3453ece6f0165be3599c034 100644 (file)
--- a/gdbserver/server.cc
+++ b/gdbserver/server.cc
@@ -2269,10 +2269,8 @@ handle_query (char *own_buf, int packet_len, int *new_packet_len_p)
         ';'.  */
       if (*p == ':')
        {
-         char **qsupported = NULL;
-         int count = 0;
-         int unknown = 0;
-         int i;
+         std::vector<std::string> qsupported;
+         std::vector<const char *> unknowns;
 
          /* Two passes, to avoid nested strtok calls in
             target_process_qsupported.  */
@@ -2280,28 +2278,23 @@ handle_query (char *own_buf, int packet_len, int *new_packet_len_p)
          for (p = strtok_r (p + 1, ";", &saveptr);
               p != NULL;
               p = strtok_r (NULL, ";", &saveptr))
-           {
-             count++;
-             qsupported = XRESIZEVEC (char *, qsupported, count);
-             qsupported[count - 1] = xstrdup (p);
-           }
+           qsupported.emplace_back (p);
 
-         for (i = 0; i < count; i++)
+         for (const std::string &feature : qsupported)
            {
-             p = qsupported[i];
-             if (strcmp (p, "multiprocess+") == 0)
+             if (feature == "multiprocess+")
                {
                  /* GDB supports and wants multi-process support if
                     possible.  */
                  if (target_supports_multi_process ())
                    cs.multi_process = 1;
                }
-             else if (strcmp (p, "qRelocInsn+") == 0)
+             else if (feature == "qRelocInsn+")
                {
                  /* GDB supports relocate instruction requests.  */
                  gdb_supports_qRelocInsn = 1;
                }
-             else if (strcmp (p, "swbreak+") == 0)
+             else if (feature == "swbreak+")
                {
                  /* GDB wants us to report whether a trap is caused
                     by a software breakpoint and for us to handle PC
@@ -2309,36 +2302,36 @@ handle_query (char *own_buf, int packet_len, int *new_packet_len_p)
                  if (target_supports_stopped_by_sw_breakpoint ())
                    cs.swbreak_feature = 1;
                }
-             else if (strcmp (p, "hwbreak+") == 0)
+             else if (feature == "hwbreak+")
                {
                  /* GDB wants us to report whether a trap is caused
                     by a hardware breakpoint.  */
                  if (target_supports_stopped_by_hw_breakpoint ())
                    cs.hwbreak_feature = 1;
                }
-             else if (strcmp (p, "fork-events+") == 0)
+             else if (feature == "fork-events+")
                {
                  /* GDB supports and wants fork events if possible.  */
                  if (target_supports_fork_events ())
                    cs.report_fork_events = 1;
                }
-             else if (strcmp (p, "vfork-events+") == 0)
+             else if (feature == "vfork-events+")
                {
                  /* GDB supports and wants vfork events if possible.  */
                  if (target_supports_vfork_events ())
                    cs.report_vfork_events = 1;
                }
-             else if (strcmp (p, "exec-events+") == 0)
+             else if (feature == "exec-events+")
                {
                  /* GDB supports and wants exec events if possible.  */
                  if (target_supports_exec_events ())
                    cs.report_exec_events = 1;
                }
-             else if (strcmp (p, "vContSupported+") == 0)
+             else if (feature == "vContSupported+")
                cs.vCont_supported = 1;
-             else if (strcmp (p, "QThreadEvents+") == 0)
+             else if (feature == "QThreadEvents+")
                ;
-             else if (strcmp (p, "no-resumed+") == 0)
+             else if (feature == "no-resumed+")
                {
                  /* GDB supports and wants TARGET_WAITKIND_NO_RESUMED
                     events.  */
@@ -2347,19 +2340,13 @@ handle_query (char *own_buf, int packet_len, int *new_packet_len_p)
              else
                {
                  /* Move the unknown features all together.  */
-                 qsupported[i] = NULL;
-                 qsupported[unknown] = p;
-                 unknown++;
+                 unknowns.push_back (feature.c_str ());
                }
            }
 
          /* Give the target backend a chance to process the unknown
             features.  */
-         target_process_qsupported (qsupported, unknown);
-
-         for (i = 0; i < count; i++)
-           free (qsupported[i]);
-         free (qsupported);
+         target_process_qsupported (unknowns);
        }
 
       sprintf (own_buf,

diff --git a/gdbserver/target.cc b/gdbserver/target.cc
index b5190e1f52a28f09e9ac019b4d009dfb23bdb47f..87f62a0b5559dd3a12090c40c5846affa4f72e37 100644 (file)
--- a/gdbserver/target.cc
+++ b/gdbserver/target.cc
@@ -599,7 +599,8 @@ process_stratum_target::read_loadmap (const char *annex,
 }
 
 void
-process_stratum_target::process_qsupported (char **features, int count)
+process_stratum_target::process_qsupported
+  (gdb::array_view<const char * const> features)
 {
   /* Nop.  */
 }

diff --git a/gdbserver/target.h b/gdbserver/target.h
index 701c8ef87675fa05327f668d7156acde0982942c..13f069f7729f4c635ba5d562888336cbb91d1643 100644 (file)
--- a/gdbserver/target.h
+++ b/gdbserver/target.h
@@ -27,6 +27,7 @@
 #include "target/wait.h"
 #include "target/waitstatus.h"
 #include "mem-break.h"
+#include "gdbsupport/array-view.h"
 #include "gdbsupport/btrace-common.h"
 #include <vector>
 
@@ -315,8 +316,9 @@ public:
                            unsigned char *myaddr, unsigned int len);
 
   /* Target specific qSupported support.  FEATURES is an array of
-     features with COUNT elements.  */
-  virtual void process_qsupported (char **features, int count);
+     features unsupported by the core of GDBserver.  */
+  virtual void process_qsupported
+    (gdb::array_view<const char * const> features);
 
   /* Return true if the target supports tracepoints, false otherwise.  */
   virtual bool supports_tracepoints ();
@@ -547,8 +549,8 @@ int kill_inferior (process_info *proc);
 #define target_async(enable) \
   the_target->async (enable)
 
-#define target_process_qsupported(features, count)     \
-  the_target->process_qsupported (features, count)
+#define target_process_qsupported(features) \
+  the_target->process_qsupported (features)
 
 #define target_supports_catch_syscall()                \
   the_target->supports_catch_syscall ()