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>

6 files changed, 253 insertions, 179 deletions

diff --git a/gdbstub/gdbstub.c b/gdbstub/gdbstub.c
index f1504af44f..e264ed04e7 100644
--- a/gdbstub/gdbstub.c
+++ b/gdbstub/gdbstub.c
@@ -29,6 +29,7 @@
 #include "qemu/module.h"
 #include "trace.h"
 #include "exec/gdbstub.h"
+#include "gdbstub/syscalls.h"
 #ifdef CONFIG_USER_ONLY
 #include "gdbstub/user.h"
 #else
@@ -38,7 +39,6 @@
 
 #include "sysemu/hw_accel.h"
 #include "sysemu/runstate.h"
-#include "semihosting/semihost.h"
 #include "exec/exec-all.h"
 #include "exec/replay-core.h"
 #include "exec/tb-flush.h"
@@ -78,41 +78,6 @@ void gdb_init_gdbserver_state(void)
 
 bool gdb_has_xml;
 
-/*
- * 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;
-}
-
 /* writes 2*len+1 bytes in buf */
 void gdb_memtohex(GString *buf, const uint8_t *mem, int len)
 {
@@ -922,7 +887,7 @@ static void handle_detach(GArray *params, void *user_ctx)
 
     if (!gdbserver_state.c_cpu) {
         /* No more process attached */
-        gdb_syscall_mode = GDB_SYS_DISABLED;
+        gdb_disable_syscalls();
         gdb_continue();
     }
     gdb_put_packet("OK");
@@ -1235,60 +1200,6 @@ static void handle_read_all_regs(GArray *params, void *user_ctx)
     gdb_put_strbuf();
 }
 
-static void handle_file_io(GArray *params, void *user_ctx)
-{
-    if (params->len >= 1 && gdbserver_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_state.current_syscall_cb(gdbserver_state.c_cpu, ret, err);
-        gdbserver_state.current_syscall_cb = NULL;
-    }
-
-    if (params->len >= 3 && get_param(params, 2)->opcode == (uint8_t)'C') {
-        gdb_put_packet("T02");
-        return;
-    }
-
-    gdb_continue();
-}
 
 static void handle_step(GArray *params, void *user_ctx)
 {
@@ -1894,7 +1805,7 @@ static int gdb_handle_packet(const char *line_buf)
     case 'F':
         {
             static const GdbCmdParseEntry file_io_cmd_desc = {
-                .handler = handle_file_io,
+                .handler = gdb_handle_file_io,
                 .cmd = "F",
                 .cmd_startswith = 1,
                 .schema = "L,L,o0"
@@ -2062,88 +1973,6 @@ void gdb_set_stop_cpu(CPUState *cpu)
     gdbserver_state.g_cpu = cpu;
 }
 
-/* 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_state.current_syscall_cb = cb;
-#ifndef CONFIG_USER_ONLY
-    vm_stop(RUN_STATE_DEBUG);
-#endif
-    p = &gdbserver_state.syscall_buf[0];
-    p_end = &gdbserver_state.syscall_buf[sizeof(gdbserver_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_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);
-}
-
 void gdb_read_byte(uint8_t ch)
 {
     uint8_t reply;
diff --git a/gdbstub/internals.h b/gdbstub/internals.h
index be0eef4850..8db61f7fb4 100644
--- a/gdbstub/internals.h
+++ b/gdbstub/internals.h
@@ -61,8 +61,6 @@ typedef struct GDBState {
     bool multiprocess;
     GDBProcess *processes;
     int process_num;
-    char syscall_buf[256];
-    gdb_syscall_complete_cb current_syscall_cb;
     GString *str_buf;
     GByteArray *mem_buf;
     int sstep_flags;
@@ -191,6 +189,12 @@ void gdb_handle_query_attached(GArray *params, void *user_ctx); /* both */
 void gdb_handle_query_qemu_phy_mem_mode(GArray *params, void *user_ctx);
 void gdb_handle_set_qemu_phy_mem_mode(GArray *params, void *user_ctx);
 
+/* sycall handling */
+void gdb_handle_file_io(GArray *params, void *user_ctx);
+bool gdb_handled_syscall(void);
+void gdb_disable_syscalls(void);
+void gdb_syscall_reset(void);
+
 /*
  * Break/Watch point support - there is an implementation for softmmu
  * and user mode.
diff --git a/gdbstub/meson.build b/gdbstub/meson.build
index 773bd4b9c9..c876222b9c 100644
--- a/gdbstub/meson.build
+++ b/gdbstub/meson.build
@@ -5,6 +5,10 @@
 #
 
 specific_ss.add(files('gdbstub.c'))
+
+# These have to built to the target ABI
+specific_ss.add(files('syscalls.c'))
+
 softmmu_ss.add(files('softmmu.c'))
 user_ss.add(files('user.c'))
 
diff --git a/gdbstub/softmmu.c b/gdbstub/softmmu.c
index d2863d0663..d3152fb6e7 100644
--- a/gdbstub/softmmu.c
+++ b/gdbstub/softmmu.c
@@ -15,6 +15,7 @@
 #include "qemu/error-report.h"
 #include "qemu/cutils.h"
 #include "exec/gdbstub.h"
+#include "gdbstub/syscalls.h"
 #include "exec/hwaddr.h"
 #include "exec/tb-flush.h"
 #include "sysemu/cpus.h"
@@ -113,9 +114,9 @@ static void gdb_vm_state_change(void *opaque, bool running, RunState state)
     if (running || gdbserver_state.state == RS_INACTIVE) {
         return;
     }
+
     /* Is there a GDB syscall waiting to be sent?  */
-    if (gdbserver_state.current_syscall_cb) {
-        gdb_put_packet(gdbserver_state.syscall_buf);
+    if (gdb_handled_syscall()) {
         return;
     }
 
@@ -384,7 +385,7 @@ int gdbserver_start(const char *device)
     }
     gdbserver_state.state = chr ? RS_IDLE : RS_INACTIVE;
     gdbserver_system_state.mon_chr = mon_chr;
-    gdbserver_state.current_syscall_cb = NULL;
+    gdb_syscall_reset();
 
     return 0;
 }
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();
+}
diff --git a/gdbstub/user.c b/gdbstub/user.c
index 3f6183e66a..3da410e221 100644
--- a/gdbstub/user.c
+++ b/gdbstub/user.c
@@ -15,6 +15,7 @@
 #include "exec/hwaddr.h"
 #include "exec/tb-flush.h"
 #include "exec/gdbstub.h"
+#include "gdbstub/syscalls.h"
 #include "gdbstub/user.h"
 #include "hw/core/cpu.h"
 #include "trace.h"