Fix gdbserver crashes on SVE/SME-enabled systems

Commit 51e6b8cfd649013ae16a3d00f1451b2531ba6bc9 fixed a
regression for SVE/SME registers on gdb's side by using a <= comparison for
regcache's raw_compare assertion check. We seem to have failed to do the same
for gdbserver's raw_compare counterpart.

With the code as it is, I'm seeing a lot of crashes for gdbserver on a machine
with SVE enabled. For instance, with the following invocation:

make check-gdb RUNTESTFLAGS="--target_board=native-gdbserver" TESTS=gdb.base/break.exp

Running /work/builds/binutils-gdb/gdb/testsuite/../../../../repos/binutils-gdb/gdb/testsuite/gdb.base/break.exp ...
FAIL: gdb.base/break.exp: test_break: run until function breakpoint
FAIL: gdb.base/break.exp: test_break: run until breakpoint set at a line number (the program is no longer running)
FAIL: gdb.base/break.exp: test_break: run until file:function(6) breakpoint (the program is no longer running)
FAIL: gdb.base/break.exp: test_break: run until file:function(5) breakpoint (the program is no longer running)
FAIL: gdb.base/break.exp: test_break: run until file:function(4) breakpoint (the program is no longer running)
FAIL: gdb.base/break.exp: test_break: run until file:function(3) breakpoint (the program is no longer running)
FAIL: gdb.base/break.exp: test_break: run until file:function(2) breakpoint (the program is no longer running)
FAIL: gdb.base/break.exp: test_break: run until file:function(1) breakpoint (the program is no longer running)
FAIL: gdb.base/break.exp: test_break: run until quoted breakpoint (the program is no longer running)
FAIL: gdb.base/break.exp: test_break: run until file:linenum breakpoint (the program is no longer running)
FAIL: gdb.base/break.exp: test_break: breakpoint offset +1
FAIL: gdb.base/break.exp: test_break: step onto breakpoint (the program is no longer running)
FAIL: gdb.base/break.exp: test_break: setting breakpoint at }
FAIL: gdb.base/break.exp: test_break: continue to breakpoint at } (the program is no longer running)
FAIL: gdb.base/break.exp: test_no_break_on_catchpoint: runto: run to main
FAIL: gdb.base/break.exp: test_break_nonexistent_line: runto: run to main
FAIL: gdb.base/break.exp: test_break_default: runto: run to main
FAIL: gdb.base/break.exp: test_break_silent_and_more: runto: run to main
FAIL: gdb.base/break.exp: test_break_line_convenience_var: runto: run to main
FAIL: gdb.base/break.exp: test_break_user_call: runto: run to main
FAIL: gdb.base/break.exp: test_finish_arguments: runto: run to main
FAIL: gdb.base/break.exp: test_next_with_recursion: kill program
FAIL: gdb.base/break.exp: test_next_with_recursion: run to factorial(6)
FAIL: gdb.base/break.exp: test_next_with_recursion: continue to factorial(5) (the program is no longer running)
FAIL: gdb.base/break.exp: test_next_with_recursion: backtrace from factorial(5)
FAIL: gdb.base/break.exp: test_next_with_recursion: next to recursive call (the program is no longer running)
FAIL: gdb.base/break.exp: test_next_with_recursion: next over recursive call (the program is no longer running)
FAIL: gdb.base/break.exp: test_next_with_recursion: backtrace from factorial(5.1)
FAIL: gdb.base/break.exp: test_next_with_recursion: continue until exit at recursive next test (the program is no longer running)
FAIL: gdb.base/break.exp: test_break_optimized_prologue: run until function breakpoint, optimized file
FAIL: gdb.base/break.exp: test_break_optimized_prologue: run until breakpoint set at small function, optimized file (the program is no longer running)
FAIL: gdb.base/break.exp: test_rbreak_shlib: rbreak junk

Adjusting the regcache raw_compare assertion check to use <= fixes
the problem on aarch64-linux on a SVE-capable system.

This patch also adds a simple selftest to gdbserver that validates this
particular case by simulating a raw_compare operation.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=32775

Approved-By: Simon Marchi <simon.marchi@efficios.com>

2 files changed, 30 insertions, 1 deletions

diff --git a/gdbserver/regcache.cc b/gdbserver/regcache.cc
index ee0c1b3..c08c9ae 100644
--- a/gdbserver/regcache.cc
+++ b/gdbserver/regcache.cc
@@ -503,7 +503,7 @@ regcache::raw_compare (int regnum, const void *buf, int offset) const
   gdb_assert (buf != NULL);
 
   gdb::array_view<const gdb_byte> regbuf = register_data (this, regnum);
-  gdb_assert (offset < regbuf.size ());
+  gdb_assert (offset <= regbuf.size ());
   regbuf = regbuf.slice (offset);
 
   return memcmp (buf, regbuf.data (), regbuf.size ()) == 0;
diff --git a/gdbserver/server.cc b/gdbserver/server.cc
index def01c1..3172cd1 100644
--- a/gdbserver/server.cc
+++ b/gdbserver/server.cc
@@ -4071,6 +4071,33 @@ test_memory_tagging_functions (void)
 	      && tags.size () == 5);
 }
 
+/* Exercise the behavior of doing a 0-length comparison for a register in a
+   register buffer, which should return true.  */
+
+static void test_registers_raw_compare_zero_length ()
+{
+  /* Start off with a dummy target description.  */
+  target_desc dummy_tdesc;
+
+  /* Make it 8 bytes long.  */
+  dummy_tdesc.registers_size = 8;
+
+  /* Add a couple dummy 32-bit registers.  */
+  dummy_tdesc.reg_defs.emplace_back ("r0", 0, 32);
+  dummy_tdesc.reg_defs.emplace_back ("r1", 32, 32);
+
+  /* Create our dummy register cache so we can invoke the raw_compare method
+     we want to validate.  */
+  regcache dummy_regcache (&dummy_tdesc);
+
+  /* Create a dummy byte buffer we can pass to the raw_compare method.  */
+  gdb_byte dummy_buffer[8];
+
+  /* Validate the 0-length comparison (due to the comparison offset being
+     equal to the length of the register) returns true.  */
+  SELF_CHECK (dummy_regcache.raw_compare (0, dummy_buffer, 4));
+}
+
 } /* namespace selftests */
 #endif /* GDB_SELF_TEST */
 
@@ -4094,6 +4121,8 @@ captured_main (int argc, char *argv[])
 
   selftests::register_test ("remote_memory_tagging",
 			    selftests::test_memory_tagging_functions);
+  selftests::register_test ("test_registers_raw_compare_zero_length",
+			    selftests::test_registers_raw_compare_zero_length);
 #endif
 
   current_directory = getcwd (NULL, 0);