gdbstub: move syscall handling to new file

Our GDB syscall support is the last chunk of code that needs target
specific support so move it to a new file. We take the opportunity to
move the syscall state into its own singleton instance and add in a
few helpers for the main gdbstub to interact with the module.

I also moved the gdb_exit() declaration into syscalls.h as it feels
pretty related and most of the callers of it treat it as such.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

Message-Id: <20230302190846.2593720-22-alex.bennee@linaro.org>
Message-Id: <20230303025805.625589-22-richard.henderson@linaro.org>

1 files changed, 235 insertions, 0 deletions

diff --git a/gdbstub/syscalls.c b/gdbstub/syscalls.c
new file mode 100644
index 0000000000..46537938d5
--- /dev/null
+++ b/gdbstub/syscalls.c
@@ -0,0 +1,235 @@
+/*
+ * GDB Syscall Handling
+ *
+ * GDB can execute syscalls on the guests behalf, currently used by
+ * the various semihosting extensions. As this interfaces with a guest
+ * ABI we need to build it per-guest (although in reality its a 32 or
+ * 64 bit target_ulong that is the only difference).
+ *
+ * Copyright (c) 2003-2005 Fabrice Bellard
+ * Copyright (c) 2023 Linaro Ltd
+ *
+ * SPDX-License-Identifier: LGPL-2.0+
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/error-report.h"
+#include "cpu.h"
+#include "semihosting/semihost.h"
+#include "sysemu/runstate.h"
+#include "gdbstub/user.h"
+#include "gdbstub/syscalls.h"
+#include "trace.h"
+#include "internals.h"
+
+/* Syscall specific state */
+typedef struct {
+    char syscall_buf[256];
+    gdb_syscall_complete_cb current_syscall_cb;
+} GDBSyscallState;
+
+static GDBSyscallState gdbserver_syscall_state;
+
+/*
+ * Return true if there is a GDB currently connected to the stub
+ * and attached to a CPU
+ */
+static bool gdb_attached(void)
+{
+    return gdbserver_state.init && gdbserver_state.c_cpu;
+}
+
+static enum {
+    GDB_SYS_UNKNOWN,
+    GDB_SYS_ENABLED,
+    GDB_SYS_DISABLED,
+} gdb_syscall_mode;
+
+/* Decide if either remote gdb syscalls or native file IO should be used. */
+int use_gdb_syscalls(void)
+{
+    SemihostingTarget target = semihosting_get_target();
+    if (target == SEMIHOSTING_TARGET_NATIVE) {
+        /* -semihosting-config target=native */
+        return false;
+    } else if (target == SEMIHOSTING_TARGET_GDB) {
+        /* -semihosting-config target=gdb */
+        return true;
+    }
+
+    /* -semihosting-config target=auto */
+    /* On the first call check if gdb is connected and remember. */
+    if (gdb_syscall_mode == GDB_SYS_UNKNOWN) {
+        gdb_syscall_mode = gdb_attached() ? GDB_SYS_ENABLED : GDB_SYS_DISABLED;
+    }
+    return gdb_syscall_mode == GDB_SYS_ENABLED;
+}
+
+/* called when the stub detaches */
+void gdb_disable_syscalls(void)
+{
+    gdb_syscall_mode = GDB_SYS_DISABLED;
+}
+
+void gdb_syscall_reset(void)
+{
+    gdbserver_syscall_state.current_syscall_cb = NULL;
+}
+
+bool gdb_handled_syscall(void)
+{
+    if (gdbserver_syscall_state.current_syscall_cb) {
+        gdb_put_packet(gdbserver_syscall_state.syscall_buf);
+        return true;
+    }
+
+    return false;
+}
+
+/*
+ * Send a gdb syscall request.
+ *  This accepts limited printf-style format specifiers, specifically:
+ *   %x  - target_ulong argument printed in hex.
+ *   %lx - 64-bit argument printed in hex.
+ *   %s  - string pointer (target_ulong) and length (int) pair.
+ */
+void gdb_do_syscallv(gdb_syscall_complete_cb cb, const char *fmt, va_list va)
+{
+    char *p;
+    char *p_end;
+    target_ulong addr;
+    uint64_t i64;
+
+    if (!gdb_attached()) {
+        return;
+    }
+
+    gdbserver_syscall_state.current_syscall_cb = cb;
+#ifndef CONFIG_USER_ONLY
+    vm_stop(RUN_STATE_DEBUG);
+#endif
+    p = &gdbserver_syscall_state.syscall_buf[0];
+    p_end = &gdbserver_syscall_state.syscall_buf[sizeof(gdbserver_syscall_state.syscall_buf)];
+    *(p++) = 'F';
+    while (*fmt) {
+        if (*fmt == '%') {
+            fmt++;
+            switch (*fmt++) {
+            case 'x':
+                addr = va_arg(va, target_ulong);
+                p += snprintf(p, p_end - p, TARGET_FMT_lx, addr);
+                break;
+            case 'l':
+                if (*(fmt++) != 'x') {
+                    goto bad_format;
+                }
+                i64 = va_arg(va, uint64_t);
+                p += snprintf(p, p_end - p, "%" PRIx64, i64);
+                break;
+            case 's':
+                addr = va_arg(va, target_ulong);
+                p += snprintf(p, p_end - p, TARGET_FMT_lx "/%x",
+                              addr, va_arg(va, int));
+                break;
+            default:
+            bad_format:
+                error_report("gdbstub: Bad syscall format string '%s'",
+                             fmt - 1);
+                break;
+            }
+        } else {
+            *(p++) = *(fmt++);
+        }
+    }
+    *p = 0;
+#ifdef CONFIG_USER_ONLY
+    gdb_put_packet(gdbserver_syscall_state.syscall_buf);
+    /*
+     * Return control to gdb for it to process the syscall request.
+     * Since the protocol requires that gdb hands control back to us
+     * using a "here are the results" F packet, we don't need to check
+     * gdb_handlesig's return value (which is the signal to deliver if
+     * execution was resumed via a continue packet).
+     */
+    gdb_handlesig(gdbserver_state.c_cpu, 0);
+#else
+    /*
+     * In this case wait to send the syscall packet until notification that
+     * the CPU has stopped.  This must be done because if the packet is sent
+     * now the reply from the syscall request could be received while the CPU
+     * is still in the running state, which can cause packets to be dropped
+     * and state transition 'T' packets to be sent while the syscall is still
+     * being processed.
+     */
+    qemu_cpu_kick(gdbserver_state.c_cpu);
+#endif
+}
+
+void gdb_do_syscall(gdb_syscall_complete_cb cb, const char *fmt, ...)
+{
+    va_list va;
+
+    va_start(va, fmt);
+    gdb_do_syscallv(cb, fmt, va);
+    va_end(va);
+}
+
+/*
+ * GDB Command Handlers
+ */
+
+void gdb_handle_file_io(GArray *params, void *user_ctx)
+{
+    if (params->len >= 1 && gdbserver_syscall_state.current_syscall_cb) {
+        uint64_t ret;
+        int err;
+
+        ret = get_param(params, 0)->val_ull;
+        if (params->len >= 2) {
+            err = get_param(params, 1)->val_ull;
+        } else {
+            err = 0;
+        }
+
+        /* Convert GDB error numbers back to host error numbers. */
+#define E(X)  case GDB_E##X: err = E##X; break
+        switch (err) {
+        case 0:
+            break;
+        E(PERM);
+        E(NOENT);
+        E(INTR);
+        E(BADF);
+        E(ACCES);
+        E(FAULT);
+        E(BUSY);
+        E(EXIST);
+        E(NODEV);
+        E(NOTDIR);
+        E(ISDIR);
+        E(INVAL);
+        E(NFILE);
+        E(MFILE);
+        E(FBIG);
+        E(NOSPC);
+        E(SPIPE);
+        E(ROFS);
+        E(NAMETOOLONG);
+        default:
+            err = EINVAL;
+            break;
+        }
+#undef E
+
+        gdbserver_syscall_state.current_syscall_cb(gdbserver_state.c_cpu,
+                                                   ret, err);
+        gdbserver_syscall_state.current_syscall_cb = NULL;
+    }
+
+    if (params->len >= 3 && get_param(params, 2)->opcode == (uint8_t)'C') {
+        gdb_put_packet("T02");
+        return;
+    }
+
+    gdb_continue();
+}