Small patch to add GDB remote file download capabilities to QEMU

vfile.patch

diff --git a/gdbstub.c b/gdbstub.c
index b470aec..54cc026 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -1907,6 +1907,91 @@ static void handle_v_kill(GdbCmdContext *gdb_ctx, void *user_ctx)
     exit(0);
 }
 
+static void handle_v_file_open(GdbCmdContext *gdb_ctx, void *user_ctx)
+{
+    const char *hex_name = gdb_ctx->params[0].data;
+    char *p;
+    int len = 0;
+    int fd;
+    unsigned long mask, mode;
+    CPUState *cpu;
+    GDBProcess *process;
+
+    while (hex_name[len] != ',') len++;
+    hextomem(gdb_ctx->mem_buf, hex_name, len);
+    gdb_ctx->mem_buf[len / 2 + 1] = '\0';
+    p = (char *)gdb_ctx->mem_buf;
+    // error_report("Param 1: %s", (char*)(gdb_ctx->mem_buf));
+    // error_report("Param 2: %lu", gdb_ctx->params[1].val_ul);
+    // error_report("Param 3: %lu", gdb_ctx->params[2].val_ul);
+    mask = gdb_ctx->params[1].val_ul;
+    mode = gdb_ctx->params[2].val_ul;
+
+    process = gdb_get_cpu_process(gdb_ctx->s, gdb_ctx->s->g_cpu);
+    cpu = get_first_cpu_in_process(gdb_ctx->s, process);
+    fd = do_openat(cpu->env_ptr, AT_FDCWD, p, mask, mode);
+    error_report("FD: %d", fd);
+    snprintf(gdb_ctx->str_buf, 1024, "F%d", fd);
+    put_packet(gdb_ctx->s, gdb_ctx->str_buf);
+}
+
+static void handle_v_file_read(GdbCmdContext *gdb_ctx, void *user_ctx)
+{
+    unsigned long fd, sz, offset;
+    fd = gdb_ctx->params[0].val_ul;
+    sz = gdb_ctx->params[1].val_ul;
+    offset = gdb_ctx->params[2].val_ul;
+
+    // error_report("Read param 2: %lu", gdb_ctx->params[1].val_ul);
+    // error_report("Read param 3: %lu", gdb_ctx->params[2].val_ul);
+
+    lseek(fd, offset, SEEK_SET);
+    if (sz > 1024) sz = 1024;
+    int ret = -TARGET_ERESTARTSYS;
+    CPUState *cpu;
+    GDBProcess *process;
+    process = gdb_get_cpu_process(gdb_ctx->s, gdb_ctx->s->g_cpu);
+    cpu = get_first_cpu_in_process(gdb_ctx->s, process);
+    while (ret == -TARGET_ERESTARTSYS) {
+        process_pending_signals(cpu->env_ptr);
+        ret = safe_read_wrap(fd, gdb_ctx->mem_buf, sz);
+    }
+    if (is_error(ret)) {
+        snprintf(gdb_ctx->str_buf, 1024, "F%d,%x", -1, -ret);
+        put_packet(gdb_ctx->s, gdb_ctx->str_buf);
+    }
+    else {
+        int idx, j;
+        idx = snprintf(gdb_ctx->str_buf, 4096, "F%x;", ret);
+        // error_report("Debug: %s", (char*)gdb_ctx->mem_buf);
+        j = idx;
+        for (int i = 0; i < ret; i++) {
+            char c;
+            c = gdb_ctx->mem_buf[i];
+            if (c == '}' || c == '#' || c == '$' || c == '*' || c == '\0') {
+                gdb_ctx->str_buf[j++] = '}';
+                gdb_ctx->str_buf[j++] = c ^ ' ';
+            }
+            else { gdb_ctx->str_buf[j++] = c; }
+        }
+        gdb_ctx->str_buf[j++] = '\0';
+        // error_report("String Debug: %s", (char*)gdb_ctx->str_buf);
+        put_packet(gdb_ctx->s, gdb_ctx->str_buf);
+    }
+}
+
+static void handle_v_file_close(GdbCmdContext *gdb_ctx, void *user_ctx)
+{
+    unsigned long fd;
+    int ret;
+    fd = gdb_ctx->params[0].val_ul;
+    ret = close(fd);
+    if (ret < 0) {
+        snprintf(gdb_ctx->str_buf, 4096, "F%x,%x", -1, -ret);
+    }
+    else snprintf(gdb_ctx->str_buf, 4096, "F%x", ret);
+    put_packet(gdb_ctx->s, gdb_ctx->str_buf);
+}
 static GdbCmdParseEntry gdb_v_commands_table[] = {
     /* Order is important if has same prefix */
     {
@@ -1931,6 +2016,24 @@ static GdbCmdParseEntry gdb_v_commands_table[] = {
         .cmd = "Kill;",
         .cmd_startswith = 1
     },
+    {
+        .handler = handle_v_file_open,
+        .cmd = "File:open:",
+        .cmd_startswith = 1,
+        .schema = "s,l,l0"
+    },
+    {
+        .handler = handle_v_file_read,
+        .cmd = "File:pread:",
+        .cmd_startswith = 1,
+        .schema = "l,l,l0"
+    },
+    {
+        .handler = handle_v_file_close,
+        .cmd = "File:close:",
+        .cmd_startswith = 1,
+        .schema = "l0"
+    },
 };
 
 static void handle_v_commands(GdbCmdContext *gdb_ctx, void *user_ctx)
@@ -2977,7 +3080,11 @@ static void create_default_process(GDBState *s)
     /* We need an available PID slot for this process */
     assert(max_pid < UINT32_MAX);
 
+    #ifdef CONFIG_USER_ONLY
+    process->pid = getpid();
+    #else
     process->pid = max_pid + 1;
+    #endif
     process->attached = false;
     process->target_xml[0] = '\0';
 }
diff --git a/linux-user/qemu.h b/linux-user/qemu.h
index 4258e41..5cf255d 100644
--- a/linux-user/qemu.h
+++ b/linux-user/qemu.h
@@ -675,3 +675,6 @@ void preexit_cleanup(CPUArchState *env, int code);
 #include "target_structs.h"
 
 #endif /* QEMU_H */
+
+int do_openat(void *cpu_env, int dirfd, const char *pathname, int flags, mode_t mode);
+ssize_t safe_read_wrap(int fd, void * buff, size_t count);
\ No newline at end of file
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 8367cb1..12ac85c 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -769,6 +769,9 @@ safe_syscall4(int, accept4, int, fd, struct sockaddr *, addr, socklen_t *, len,
               int, flags)
 safe_syscall2(int, nanosleep, const struct timespec *, req,
               struct timespec *, rem)
+abi_long safe_read_wrap(int fd, void * buff, size_t count) {
+  return get_errno(safe_read(fd, buff, count));
+}
 #ifdef TARGET_NR_clock_nanosleep
 safe_syscall4(int, clock_nanosleep, const clockid_t, clock, int, flags,
               const struct timespec *, req, struct timespec *, rem)
@@ -7061,7 +7064,7 @@ static int open_hardware(void *cpu_env, int fd)
 }
 #endif
 
-static int do_openat(void *cpu_env, int dirfd, const char *pathname, int flags, mode_t mode)
+int do_openat(void *cpu_env, int dirfd, const char *pathname, int flags, mode_t mode)
 {
     struct fake_open {
         const char *filename;