sim: eBPF simulator

This patch introduces the basics of an instruction-simulator for eBPF.
The simulator is based on CGEN.

gdb/ChangeLog:

2020-08-04  Jose E. Marchesi  <jose.marchesi@oracle.com>

	* configure.tgt: Set gdb_sim for bpf-*-* targets.

sim/ChangeLog:

2020-08-04  Jose E. Marchesi  <jose.marchesi@oracle.com>
	    David Faust <david.faust@oracle.com>

	* configure.tgt (sim_arch): Add entry for bpf-*-*.
	* configure: Regenerate.
	* MAINTAINERS: Add maintainer for the BPF simulator.
	* bpf/Makefile.in: New file.
	* bpf/bpf-helpers.c: Likewise.
	* bpf/bpf-helpers.def: Likewise.
	* bpf/bpf-helpers.h: Likewise.
	* bpf/bpf-sim.h: Likewise.
	* bpf/bpf.c: Likewise.
	* bpf/config.in: Likewise.
	* bpf/configure.ac: Likewise.
	* bpf/decode.h: Likewise.
	* bpf/eng.h: Likewise.
	* bpf/mloop.in: Likewise.
	* bpf/sim-if.c: Likewise.
	* bpf/sim-main.h: Likewise.
	* bpf/traps.c: Likewise.
	* bpf/configure: Generate.
	* bpf/aclocal.m4: Likewise.

sim/testsuite/ChangeLog:

2020-08-04  David Faust  <david.faust@oracle.com>
	    Jose E. Marchesi  <jose.marchesi@oracle.com>

	* configure: Regenerate.
	* sim/bpf/allinsn.exp: New file.
	* sim/bpf/alu.s: Likewise.
	* sim/bpf/alu32.s: Likewise.
	* sim/bpf/endbe.s: Likewise.
	* sim/bpf/endle.s: Likewise.
	* sim/bpf/jmp.s: Likewise.
	* sim/bpf/jmp32.s: Likewise.
	* sim/bpf/ldabs.s: Likewise.
	* sim/bpf/mem.s: Likewise.
	* sim/bpf/mov.s: Likewise.
	* sim/bpf/testutils.inc: Likewise.
	* sim/bpf/xadd.s: Likewise.

1 files changed, 175 insertions, 0 deletions

diff --git a/sim/bpf/bpf-helpers.c b/sim/bpf/bpf-helpers.c
new file mode 100644
index 0000000..cec5645
--- /dev/null
+++ b/sim/bpf/bpf-helpers.c
@@ -0,0 +1,175 @@
+/* Emulation of eBPF helpers.
+   Copyright (C) 2020 Free Software Foundation, Inc.
+
+   This file is part of GDB, the GNU debugger.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* BPF programs rely on the existence of several helper functions,
+   which are provided by the kernel.  This simulator provides an
+   implementation of the helpers, which can be customized by the
+   user.  */
+
+#define WANT_CPU_BPFBF
+#define WANT_CPU bpfbf
+
+#include "sim-main.h"
+#include "cgen-mem.h"
+#include "cgen-ops.h"
+#include "cpu.h"
+
+/* bpf_trace_printk is a printk-like facility for debugging.
+
+   In the kernel, it appends a line to the Linux's tracing debugging
+   interface.
+
+   In this simulator, it uses the simulator's tracing interface
+   instead.
+
+   The format tags recognized by this helper are:
+   %d, %i, %u, %x, %ld, %li, %lu, %lx, %lld, %lli, %llu, %llx,
+   %p, %s
+
+   A maximum of three tags are supported.
+
+   This helper returns the number of bytes written, or a negative
+   value in case of failure.  */
+
+int
+bpf_trace_printk (SIM_CPU *current_cpu)
+{
+  va_list ap;
+  SIM_DESC sd = CPU_STATE (current_cpu);
+
+  DI fmt_address;
+  uint32_t size, tags_processed;
+  size_t i, bytes_written = 0;
+
+  /* The first argument is the format string, which is passed as a
+     pointer in %r1.  */
+  fmt_address = GET_H_GPR (1);
+
+  /* The second argument is the length of the format string, as an
+     unsigned 32-bit number in %r2.  */
+  size = GET_H_GPR (2);
+
+  /* Read the format string from the memory pointed by %r2, printing
+     out the stuff as we go.  There is a maximum of three format tags
+     supported, which are read from %r3, %r4 and %r5 respectively.  */
+  for (i = 0, tags_processed = 0; i < size;)
+    {
+      QI c = GETMEMUQI (current_cpu, CPU_PC_GET (current_cpu),
+                        fmt_address + i);
+
+      switch (c)
+        {
+        case '%':
+          /* Check we are not exceeding the limit of three format
+             tags.  */
+          if (tags_processed > 2)
+            return -1; /* XXX look for kernel error code.  */
+
+          /* Depending on the kind of tag, extract the value from the
+             proper argument.  */
+          if (i++ >= size)
+            return -1; /* XXX look for kernel error code.  */
+
+          UDI value = GET_H_GPR (3 + tags_processed);
+
+          switch ((GETMEMUQI (current_cpu, CPU_PC_GET (current_cpu),
+                             fmt_address + i)))
+            {
+            case 'd':
+              trace_printf (sd, current_cpu, "%d", value);
+              break;
+            case 'i':
+              trace_printf (sd, current_cpu, "%i", value);
+              break;
+            case 'u':
+              trace_printf (sd, current_cpu, "%u", value);
+              break;
+            case 'x':
+              trace_printf (sd, current_cpu, "%x", value);
+              break;
+            case 'l':
+              {
+                if (i++ >= size)
+                  return -1;
+                switch (GETMEMUQI (current_cpu, CPU_PC_GET (current_cpu),
+                             fmt_address + i))
+                  {
+                  case 'd':
+                    trace_printf (sd, current_cpu, "%ld", value);
+                    break;
+                  case 'i':
+                    trace_printf (sd, current_cpu, "%li", value);
+                    break;
+                  case 'u':
+                    trace_printf (sd, current_cpu, "%lu", value);
+                    break;
+                  case 'x':
+                    trace_printf (sd, current_cpu, "%lx", value);
+                    break;
+                  case 'l':
+                    {
+                      if (i++ >= size)
+                        return -1;
+                      switch (GETMEMUQI (current_cpu, CPU_PC_GET (current_cpu),
+                                fmt_address + i)) {
+                        case 'd':
+                          trace_printf (sd, current_cpu, "%lld", value);
+                          break;
+                        case 'i':
+                          trace_printf (sd, current_cpu, "%lli", value);
+                          break;
+                        case 'u':
+                          trace_printf (sd, current_cpu, "%llu", value);
+                          break;
+                        case 'x':
+                          trace_printf (sd, current_cpu, "%llx", value);
+                          break;
+                        default:
+                          assert (0);
+                          break;
+                      }
+                      break;
+                    }
+                  default:
+                    assert (0);
+                    break;
+                }
+                break;
+              }
+            default:
+              /* XXX completeme */
+              assert (0);
+              break;
+            }
+
+          tags_processed++;
+          i++;
+          break;
+        case '\0':
+          i = size;
+          break;
+        default:
+          trace_printf (sd, current_cpu, "%c", c);
+          bytes_written++;
+          i++;
+          break;
+        }
+    }
+
+  return bytes_written;
+}