On Tue, Nov 5, 2024 at 5:37 AM Richard Henderson <richard.hender...@linaro.org> wrote: > > On 10/30/24 14:10, Noah Goldstein wrote: > > The new option '-qemu-children' makes it so that on `execve` the child > > process will be launch by the same `qemu` executable that is currently > > running along with its current commandline arguments. > > > > The motivation for the change is to make it so that plugins running > > through `qemu` can continue to run on children. Why not just > > `binfmt`?: Plugins can be desirable regardless of system/architecture > > emulation, and can sometimes be useful for elf files that can run > > natively. Enabling `binfmt` for all natively runnable elf files may > > not be desirable. > > > > Signed-off-by: Noah Goldstein <goldstein....@gmail.com> > > --- > > linux-user/main.c | 21 ++++++ > > linux-user/syscall.c | 21 ++++-- > > linux-user/user-internals.h | 4 ++ > > tests/tcg/multiarch/Makefile.target | 8 +++ > > .../linux/linux-execve-qemu-children.c | 68 +++++++++++++++++++ > > 5 files changed, 117 insertions(+), 5 deletions(-) > > create mode 100644 tests/tcg/multiarch/linux/linux-execve-qemu-children.c > > > > diff --git a/linux-user/main.c b/linux-user/main.c > > index 8143a0d4b0..5e3d41dc2b 100644 > > --- a/linux-user/main.c > > +++ b/linux-user/main.c > > @@ -81,6 +81,10 @@ unsigned long mmap_min_addr; > > uintptr_t guest_base; > > bool have_guest_base; > > > > +bool qemu_dup_for_children; > > +int qemu_argc; > > +char **qemu_argv; > > + > > /* > > * Used to implement backwards-compatibility for the `-strace`, and > > * QEMU_STRACE options. Without this, the QEMU_LOG can be overwritten by > > @@ -451,6 +455,11 @@ static void handle_arg_jitdump(const char *arg) > > perf_enable_jitdump(); > > } > > > > +static void handle_arg_qemu_children(const char *arg) > > +{ > > + qemu_dup_for_children = true; > > +} > > + > > static QemuPluginList plugins = QTAILQ_HEAD_INITIALIZER(plugins); > > > > #ifdef CONFIG_PLUGIN > > @@ -526,6 +535,10 @@ static const struct qemu_argument arg_table[] = { > > "", "Generate a /tmp/perf-${pid}.map file for perf"}, > > {"jitdump", "QEMU_JITDUMP", false, handle_arg_jitdump, > > "", "Generate a jit-${pid}.dump file for perf"}, > > + {"qemu-children", > > + "QEMU_CHILDREN", false, handle_arg_qemu_children, > > + "", "Run child processes (created with execve) with qemu " > > + "(as instantiated for the parent)"}, > > {NULL, NULL, false, NULL, NULL, NULL} > > }; > > > > @@ -729,6 +742,14 @@ int main(int argc, char **argv, char **envp) > > > > optind = parse_args(argc, argv); > > > > + if (qemu_dup_for_children) { > > + qemu_argc = optind; > > + qemu_argv = g_new0(char *, qemu_argc); > > + for (i = 0; i < optind; ++i) { > > + qemu_argv[i] = strdup(argv[i]); > > g_strdup. ack > > > + bool through_qemu = dirfd == AT_FDCWD && qemu_dup_for_children; > > Why is this limited to AT_FDCWD? Why not for execvat too? >
We could, initially it was because AFAICT qemu doesn't support executing a program relative to another dir, but it would be simple enough to just join the relative program path and path dirfd points to. Want me to add support? > > @@ -8628,9 +8631,16 @@ static int do_execv(CPUArchState *cpu_env, int dirfd, > > } > > > > const char *exe = p; > > - if (is_proc_myself(p, "exe")) { > > + if (through_qemu) { > > + int i; > > + for (i = 0; i < argp_offset; ++i) { > > + argp[i] = qemu_argv[i]; > > + } > > + exe = qemu_argv[0]; > > + } else if (is_proc_myself(p, "exe")) { > > exe = exec_path; > > } > > + > > You still need to handle is_proc_myself, for the guest binary. > > I wonder if those two cases are related. Do we need to also add an argument > so that we > can pass the executable to the next qemu via file descriptor? I.e. execvat > becomes > > f = openat() > execv(qemu, "-execfd", f) > > and is_proc_myself uses execfd, which we already have open. > > > r~