From nobody Sun Jul 26 10:59:48 2026 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=pass(p=none dis=none) header.from=sjtu.edu.cn ARC-Seal: i=1; a=rsa-sha256; t=1782921488; cv=none; d=zohomail.com; s=zohoarc; b=iJZOmEKvtnVK0wnY/wPeVqeaCc7IqteydxM7Ccl8AX8ODzTjHuQ0IrEEhTxLuDreZHX1uB2hsIsb0OWcrRSVNc/eetF3j21DLaO6//h2RxFx/K4RNNX5HoftRp4voenF3ySJ6U1hQ22WLuMsWI1mAPhrIOJLXW8jUB8OE0OvCYc= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1782921488; h=Content-Transfer-Encoding:Cc:Cc:Date:Date:From:From:In-Reply-To:List-Subscribe:List-Post:List-Id:List-Archive:List-Help:List-Unsubscribe:MIME-Version:Message-ID:References:Sender:Subject:Subject:To:To:Message-Id:Reply-To; bh=FNxJ7PM8dFzTlysTNLwZbS6moXzU4rylyVRuNHMU2mw=; b=MPqAqDEZIf0hPWyy1ppdSut9H1A2Rf/dA/iCuiIX2bQ+JVzwZO+ILkeq52v7PM39tbOfq6tLgDuKIh6FMmfZT9SeWAJdZI+7zyydjXTAnGF47u+PQf8bUX/vRapat0aiJqcqf+zRU+ppFvZ9G0AmjQ71ep086Y9xMB6iHMiKM08= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=pass header.from= (p=none dis=none) Return-Path: Received: from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1782921487179524.3183262119495; Wed, 1 Jul 2026 08:58:07 -0700 (PDT) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wexJh-0002XH-GT; Wed, 01 Jul 2026 11:57:37 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wexJf-0002Wz-4s for qemu-devel@nongnu.org; Wed, 01 Jul 2026 11:57:35 -0400 Received: from smtp186.sjtu.edu.cn ([202.120.2.186]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wexJc-0005kN-Kg for qemu-devel@nongnu.org; Wed, 01 Jul 2026 11:57:34 -0400 Received: from proxy188.sjtu.edu.cn (smtp188.sjtu.edu.cn [202.120.2.188]) by smtp186.sjtu.edu.cn (Postfix) with ESMTPS id BF6402FF40C; Wed, 1 Jul 2026 15:57:07 +0000 (UTC) Received: from pc.. (unknown [202.120.40.100]) by proxy188.sjtu.edu.cn (Postfix) with ESMTPSA id 152FC37C951; Wed, 1 Jul 2026 23:57:07 +0800 (CST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=sjtu.edu.cn; s=default; t=1782921427; bh=23c7Vi3Bj6545DtDxLAEHiAJBS3g84GNnJP4iGwRlCc=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=a/lN0K6Y3waWQhbJOyig7GyHdSj6ZSrKaY/4NtxPAzH2NRRZdLU+JTaHGeaaY/x+W 2fWgdVqdGs5IKfe6Dpf/aPrHW+pLPPNS/bzXahveTHv4/5EQ0eMbvulDGL6vL87/Hf ZbtC/dE1Qg+zZACvletSOsrdtOtGF8njMI83A2QHxYI1ma7R73j1MZMfgkt8N1pfWr IZGWEJB6h1SPCZ66osGZTWA8bWtnSKoL21txpCERMssN0kcAMvG0OUPTT/Nb/3zmPB Nc08aGQZbLKtOjCWZKic+/wnSnDmnrminsfav36XHYjkx/VFv5uUCfrcFMuodueg7L qLG2e0B5bubIg== From: Ziyang Zhang To: qemu-devel Cc: Riku Voipio , Laurent Vivier , Alex Bennee , Alexandre Iooss , Mahmoud Mandour , Pierrick Bouvier , Richard Henderson , Zhengwei Qi , Yun Wang , Mingyuan Xia , Kailiang Xu , Ziyang Zhang Subject: [PATCH v5 1/2] contrib/plugins: add a minimal dlcall plugin Date: Wed, 1 Jul 2026 23:57:04 +0800 Message-Id: <20260701155705.1737328-2-functioner@sjtu.edu.cn> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260701155705.1737328-1-functioner@sjtu.edu.cn> References: <20260701155705.1737328-1-functioner@sjtu.edu.cn> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists1p.gnu.org; Received-SPF: pass client-ip=202.120.2.186; envelope-from=functioner@sjtu.edu.cn; helo=smtp186.sjtu.edu.cn X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @sjtu.edu.cn) X-ZM-MESSAGEID: 1782921492175158500 Content-Type: text/plain; charset="utf-8" Add a minimal dlcall plugin that lets the guest invoke host functions through magic system calls. The plugin registers a vCPU syscall filter callback that intercepts a reserved syscall number and dispatches a set of pass-through operations: querying host attributes, loading and freeing shared libraries, resolving symbols, retrieving the last library error, and invoking a host function through a common interface. The magic syscall number defaults to 4096 and can be overridden at load time with the "syscall_num=3DN" argument; values low enough to clash with a real syscall are rejected. Co-authored-by: Kailiang Xu Co-authored-by: Mingyuan Xia Signed-off-by: Ziyang Zhang --- contrib/plugins/dlcall.c | 246 ++++++++++++++++++++++++++++++++++++ contrib/plugins/meson.build | 5 + 2 files changed, 251 insertions(+) create mode 100644 contrib/plugins/dlcall.c diff --git a/contrib/plugins/dlcall.c b/contrib/plugins/dlcall.c new file mode 100644 index 0000000000..187fdf05b8 --- /dev/null +++ b/contrib/plugins/dlcall.c @@ -0,0 +1,246 @@ +/* + * Copyright (C) 2026, Ziyang Zhang + * + * dlcall plugin: lets a linux-user guest invoke host functions by issuing= a + * magic system call. The guest can ask QEMU to dlopen() a host shared + * library, dlsym() a symbol, and call it with guest-supplied arguments. + * + * The plugin is minimal and prescribes nothing about how a library is + * thunked. Any toolchain can implement the userspace side. Lorelei is a + * complete, MIT-licensed implementation (guest/host runtimes plus a thunk + * compiler that generates thunks from a library's headers): + * https://github.com/rover2024/lorelei + * + * See docs/about/emulation.rst|Dlcall for details and examples. + * + * WARNING: trusted guests only. The guest can load arbitrary host librari= es + * and execute arbitrary host code with arbitrary arguments, i.e. full code + * execution in the QEMU host process. It is NOT a sandbox and provides no + * isolation; only load it for guests you fully trust. + * + * WARNING: requires guest_base =3D=3D 0, which is qemu-user's default. Po= inter + * operands are dereferenced as host addresses directly, and the invoked h= ost + * functions dereference guest pointers with no address translation, so gu= est + * and host must share a single address space. A non-zero guest_base (e.g.= set + * via -B/-R) would make every pointer off by guest_base and hit unrelated + * host memory. + * + * SPDX-License-Identifier: GPL-2.0-or-later + */ + +#include +#include +#include +#include +#include +#include + +#include + +QEMU_PLUGIN_EXPORT int qemu_plugin_version =3D QEMU_PLUGIN_VERSION; + +/* + * The magic system call number for dlcall. + * + * It defaults to DLCALL_SYSCALL_DEFAULT and can be overridden at load time + * with the "syscall_num=3DN" argument. To avoid hijacking a real syscall = the + * guest might issue, N must be at least DLCALL_SYSCALL_MIN: every Linux A= BI + * keeps its syscall numbers well below this; numbers from here up are fre= e. + */ +enum { + DLCALL_SYSCALL_DEFAULT =3D 4096, + DLCALL_SYSCALL_MIN =3D 4096, +}; + +static int64_t dlcall_syscall_num =3D DLCALL_SYSCALL_DEFAULT; + +/* + * dlcall calling convention. + * + * The guest issues the magic system call (dlcall_syscall_num). The first + * argument (a1) is one of the call IDs below; the remaining arguments (a2= , a3, + * a4, ...) are that ID's operands. All pointer operands are guest virtual + * addresses that the plugin dereferences as host addresses directly (see = the + * guest_base requirement above). Results are written back through + * caller-provided "out" pointers rather than returned in the syscall valu= e. + * + * The syscall return value (*sysret) only reports dispatch status: 0 on a + * recognised ID, -EINVAL for an unknown one. The actual success/failure o= f an + * operation (e.g. a NULL handle from dlopen) is delivered through its out + * pointer, exactly like the underlying libdl call. + * + * Operands per ID: + * + * DLCALL_ID_GET_HOST_ATTRIBUTE + * a2 const char *key in: attribute name to query + * a3 const char **attr_ptr out: matching value, or NULL if unknown + * + * DLCALL_ID_LOAD_LIBRARY (wraps dlopen) + * a2 const char *path in: library path + * a3 int flags in: dlopen() flags (e.g. RTLD_NOW) + * a4 void **handle_ptr out: library handle, or NULL on failure + * + * DLCALL_ID_GET_PROC_ADDRESS (wraps dlsym) + * a2 void *handle in: library handle + * a3 const char *name in: symbol name + * a4 void **entry_ptr out: symbol address, or NULL if not found + * + * DLCALL_ID_FREE_LIBRARY (wraps dlclose) + * a2 void *handle in: library handle + * a3 int *ret_ptr out: dlclose() return value (0 on succes= s) + * + * DLCALL_ID_GET_LIBRARY_ERROR (wraps dlerror) + * a2 const char **error_ptr out: last libdl error string, or NULL + * + * DLCALL_ID_INVOKE_PROC (calls the symbol) + * a2 void *proc in: function pointer, signature + * void (*)(void *arg1, void *arg2) + * a3 void *arg1 in: first argument forwarded to proc + * a4 void *arg2 in: second argument forwarded to proc + */ +enum DlcallID { + DLCALL_ID_GET_HOST_ATTRIBUTE, + DLCALL_ID_LOAD_LIBRARY, + DLCALL_ID_GET_PROC_ADDRESS, + DLCALL_ID_FREE_LIBRARY, + DLCALL_ID_GET_LIBRARY_ERROR, + DLCALL_ID_INVOKE_PROC, +}; + +static inline const char *query_host_attribute(const char *key) +{ + if (strcmp(key, "emu") =3D=3D 0) { + return "qemu"; + } + return NULL; +} + +static inline void invoke_proc(void *proc, void *arg1, void *arg2) +{ + typedef void (*Func)(void * /*arg1*/, void * /*arg2*/); + Func func =3D (Func) proc; + func(arg1, arg2); +} + +static bool vcpu_syscall_filter(unsigned int vcpu_index, + int64_t num, uint64_t a1, uint64_t a2, + uint64_t a3, uint64_t a4, uint64_t a5, + uint64_t a6, uint64_t a7, uint64_t a8, + int64_t *sysret, void *userdata) +{ + if (num =3D=3D dlcall_syscall_num) { + switch (a1) { + /* Query host attribute by a reserved key. */ + case DLCALL_ID_GET_HOST_ATTRIBUTE: { + const char *key =3D (const char *) a2; + const char **attr_ptr =3D (const char **) a3; + assert(attr_ptr); + *attr_ptr =3D query_host_attribute(key); + *sysret =3D 0; + break; + } + + /* Load a shared library. */ + case DLCALL_ID_LOAD_LIBRARY: { + const char *path =3D (const char *) a2; + int flags =3D (int) a3; + void **handle_ptr =3D (void **) a4; + assert(handle_ptr); + *handle_ptr =3D dlopen(path, flags); + *sysret =3D 0; + break; + } + + /* Get the address of a function in a shared library. */ + case DLCALL_ID_GET_PROC_ADDRESS: { + void *handle =3D (void *) a2; + const char *name =3D (const char *) a3; + void **entry_ptr =3D (void **) a4; + assert(entry_ptr); + *entry_ptr =3D dlsym(handle, name); + *sysret =3D 0; + break; + } + + /* Free a shared library. */ + case DLCALL_ID_FREE_LIBRARY: { + void *handle =3D (void *) a2; + int *ret_ptr =3D (int *) a3; + *ret_ptr =3D dlclose(handle); + *sysret =3D 0; + break; + } + + /* Get the last error message for a library event. */ + case DLCALL_ID_GET_LIBRARY_ERROR: { + const char **error_ptr =3D (const char **) a2; + *error_ptr =3D dlerror(); + *sysret =3D 0; + break; + } + + /* Invoke a function of a common interface. */ + case DLCALL_ID_INVOKE_PROC: { + void *proc =3D (void *) a2; + void *arg1 =3D (void *) a3; + void *arg2 =3D (void *) a4; + assert(proc); + invoke_proc(proc, arg1, arg2); + *sysret =3D 0; + break; + } + + default: + *sysret =3D -EINVAL; + break; + } + return true; + } + return false; +} + +QEMU_PLUGIN_EXPORT int qemu_plugin_install(qemu_plugin_id_t id, + const qemu_info_t *info, + int argc, char **argv) +{ + if (info->system_emulation) { + fprintf(stderr, "plugin dlcall: only useful for user emulation\n"); + return -1; + } + + for (int i =3D 0; i < argc; i++) { + char *opt =3D argv[i]; + g_auto(GStrv) tokens =3D g_strsplit(opt, "=3D", 2); + if (g_strcmp0(tokens[0], "syscall_num") =3D=3D 0) { + const char *val =3D tokens[1]; + char *endptr =3D NULL; + guint64 num; + if (!val || *val =3D=3D '\0') { + fprintf(stderr, + "plugin dlcall: missing value for syscall_num\n"); + return -1; + } + num =3D g_ascii_strtoull(val, &endptr, 0); + if (*endptr !=3D '\0' || g_strrstr(val, "-") !=3D NULL) { + fprintf(stderr, + "plugin dlcall: invalid syscall_num '%s'\n", val); + return -1; + } + if (num < DLCALL_SYSCALL_MIN || num > G_MAXINT64) { + fprintf(stderr, + "plugin dlcall: syscall_num %s is out of range; " + "it must be >=3D %d to avoid clashing with a real " + "syscall\n", val, DLCALL_SYSCALL_MIN); + return -1; + } + dlcall_syscall_num =3D (int64_t) num; + } else { + fprintf(stderr, "plugin dlcall: unknown option '%s'\n", opt); + return -1; + } + } + + qemu_plugin_register_vcpu_syscall_filter_cb(id, vcpu_syscall_filter, N= ULL); + + return 0; +} diff --git a/contrib/plugins/meson.build b/contrib/plugins/meson.build index 099319e7a1..e7fc4d6d8f 100644 --- a/contrib/plugins/meson.build +++ b/contrib/plugins/meson.build @@ -19,6 +19,11 @@ if host_os !=3D 'windows' contrib_plugins +=3D 'lockstep.c' endif =20 +if host_os =3D=3D 'linux' + # dlcall passes guest calls through to host libraries; linux-user only + contrib_plugins +=3D 'dlcall.c' +endif + if 'cpp' in all_languages contrib_plugins +=3D 'cpp.cpp' endif --=20 2.34.1 From nobody Sun Jul 26 10:59:48 2026 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; 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(unknown [202.120.40.100]) by proxy188.sjtu.edu.cn (Postfix) with ESMTPSA id 376E2380C9A; Wed, 1 Jul 2026 23:57:07 +0800 (CST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=sjtu.edu.cn; s=default; t=1782921427; bh=yXCUUvPgdYz7tcDJMijkLwj07Wj7W2aPdemmMHum/pU=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=V5JStoezch8rs4qqm/oE4v2sDE5XHQN36uS7/PQZNwKmB2SHRehXYBCfzIAu0+dxg 7Rj1NrNIEB08MejLc/tt4jQXjWTjlSxsht0Z0LQ1BuzfvBw5V+4kDI6SuZ75SN+PUr u3kj5tS+OkcGNeLbgwyP+vwscePtoRN28pKD5i7q8xxT8HX+04alyRjdHAU4B1rk5J hcBcVQKQS5nr4kss6Hvyig808ab1I1/5sAEca3usHtUhu3iVGuXjPgVvefljYiwElF 5RaUklxPh7yjSmv/LDearHWX6rVKsS5OQmWjLQvY0cGJxLUDbdyGoORQuyTD56MHwW AQBBXzlbhVf1A== From: Ziyang Zhang To: qemu-devel Cc: Riku Voipio , Laurent Vivier , Alex Bennee , Alexandre Iooss , Mahmoud Mandour , Pierrick Bouvier , Richard Henderson , Zhengwei Qi , Yun Wang , Mingyuan Xia , Kailiang Xu , Ziyang Zhang Subject: [PATCH v5 2/2] docs/about/emulation: document the dlcall plugin Date: Wed, 1 Jul 2026 23:57:05 +0800 Message-Id: <20260701155705.1737328-3-functioner@sjtu.edu.cn> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260701155705.1737328-1-functioner@sjtu.edu.cn> References: <20260701155705.1737328-1-functioner@sjtu.edu.cn> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists1p.gnu.org; Received-SPF: pass client-ip=202.120.2.186; envelope-from=functioner@sjtu.edu.cn; helo=smtp186.sjtu.edu.cn X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @sjtu.edu.cn) X-ZM-MESSAGEID: 1782921492111158500 Content-Type: text/plain; charset="utf-8" Document the dlcall plugin under Example Plugins: what it does, the trusted- guests and guest_base =3D=3D 0 constraints, how to load it, and a pointer to Lorelei, a complete userspace implementation, for prebuilt thunks and a runnable example. Signed-off-by: Ziyang Zhang --- docs/about/emulation.rst | 55 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 55 insertions(+) diff --git a/docs/about/emulation.rst b/docs/about/emulation.rst index 3b4c365933..8877708d18 100644 --- a/docs/about/emulation.rst +++ b/docs/about/emulation.rst @@ -1046,6 +1046,61 @@ Count traps This plugin counts the number of interrupts (asynchronous events), excepti= ons (synchronous events) and host calls (e.g. semihosting) per cpu. =20 +Dlcall +...... + +``contrib/plugins/dlcall.c`` + +This plugin lets a linux-user guest call functions in the host's native sh= ared +libraries instead of emulating them, turning slow instruction-by-instructi= on +emulation of a library into a native host call. For example, the stock zlib +``minizip`` utility compresses several times faster, because the actual +``deflate`` runs on the host's native libz while ``minizip`` itself stays +emulated. + +The guest issues a reserved "magic" system call (4096 by default, configur= able +with ``syscall_num=3DN``) whose first argument selects a pass-through oper= ation: +dlopen/dlclose a host library, dlsym a symbol, and invoke a resolved host +function. The plugin performs the operation on the host and consumes the +syscall, so the real kernel never sees it. + +.. warning:: + + Trusted guests only. The guest can load arbitrary host libraries and run + arbitrary code in the QEMU host process. The plugin is not a sandbox and + provides no isolation. It also requires ``guest_base =3D=3D 0`` (qemu-u= ser's + default), as guest pointers are dereferenced as host addresses with no + translation. + +The plugin is deliberately minimal and knows nothing about any particular +library or its calling convention. Turning a real library into working thu= nks, +including argument marshalling, callbacks and variadic functions, is done +entirely in userspace, and any toolchain can implement the interface. +`Lorelei `_ is a complete, MIT-licen= sed +implementation: it provides the guest and host runtimes and a Thunk Library +Compiler that generates the thunks from a library's headers, with prebuilt +thunks (zlib, lzma, ...) for x86_64, aarch64 and riscv64 hosts. + +Loading the plugin is all that is required from QEMU's side: + +.. code-block:: shell + + qemu-x86_64 -plugin contrib/plugins/libdlcall.so ... + +See `Lorelei `_ for prebuilt thunk t= rees, +the runtime environment they expect, and a full runnable example (for inst= ance, +running an unmodified ``minizip`` over the host's native libz). + +.. list-table:: Dlcall plugin arguments + :widths: 20 80 + :header-rows: 1 + + * - Option + - Description + * - syscall_num=3DN + - The magic syscall number the guest issues (default 4096). Must be hi= gh + enough not to clash with a real syscall. + Other emulation features ------------------------ =20 --=20 2.34.1