On Fri, Jan 14, 2022 at 4:40 AM Peter Maydell wrote: > On Sun, 9 Jan 2022 at 16:36, Warner Losh wrote: > > > > setup_frame sets up a signalled stack frame. Associated routines to > > extract the pointer to the stack frame and to support alternate stacks. > > > > Signed-off-by: Stacey Son > > Signed-off-by: Kyle Evans > > Signed-off-by: Warner Losh > > --- > > bsd-user/signal.c | 166 ++++++++++++++++++++++++++++++++++++++++------ > > 1 file changed, 144 insertions(+), 22 deletions(-) > > > > diff --git a/bsd-user/signal.c b/bsd-user/signal.c > > index 8dadc9a39a7..8e1427553da 100644 > > --- a/bsd-user/signal.c > > +++ b/bsd-user/signal.c > > @@ -30,11 +30,27 @@ > > * fork. > > */ > > > > +static target_stack_t target_sigaltstack_used = { > > + .ss_sp = 0, > > + .ss_size = 0, > > + .ss_flags = TARGET_SS_DISABLE, > > +}; > > sigaltstacks are per-thread, so this needs to be in the TaskState, > not global. (We fixed this in linux-user in commit 5bfce0b74fbd5d5 > in 2019: the change is relatively small.) > Done. I saw go mentioned, which I know doesn't work today, so it's a good step in that direction... > > + > > static struct target_sigaction sigact_table[TARGET_NSIG]; > > static void host_signal_handler(int host_sig, siginfo_t *info, void > *puc); > > static void target_to_host_sigset_internal(sigset_t *d, > > const target_sigset_t *s); > > > > +static inline int on_sig_stack(unsigned long sp) > > +{ > > + return sp - target_sigaltstack_used.ss_sp < > target_sigaltstack_used.ss_size; > > +} > > + > > +static inline int sas_ss_flags(unsigned long sp) > > +{ > > + return target_sigaltstack_used.ss_size == 0 ? SS_DISABLE : > on_sig_stack(sp) > > + ? SS_ONSTACK : 0; > > +} > > > > int host_to_target_signal(int sig) > > { > > @@ -336,28 +352,6 @@ void queue_signal(CPUArchState *env, int sig, > target_siginfo_t *info) > > return; > > } > > > > -static int fatal_signal(int sig) > > -{ > > - > > - switch (sig) { > > - case TARGET_SIGCHLD: > > - case TARGET_SIGURG: > > - case TARGET_SIGWINCH: > > - case TARGET_SIGINFO: > > - /* Ignored by default. */ > > - return 0; > > - case TARGET_SIGCONT: > > - case TARGET_SIGSTOP: > > - case TARGET_SIGTSTP: > > - case TARGET_SIGTTIN: > > - case TARGET_SIGTTOU: > > - /* Job control signals. */ > > - return 0; > > - default: > > - return 1; > > - } > > -} > > There wasn't any need to move this function, I think ? > No, there was some other conflict during rebase getting the patch train ready that I thought I'd cleaned up, but this was fallout from that which I overlooked. I've undone it... > > - > > /* > > * Force a synchronously taken QEMU_SI_FAULT signal. For QEMU the > > * 'force' part is handled in process_pending_signals(). > > @@ -484,6 +478,134 @@ static void host_signal_handler(int host_sig, > siginfo_t *info, void *puc) > > cpu_exit(thread_cpu); > > } > > > > +static int fatal_signal(int sig) > > +{ > > + > > + switch (sig) { > > + case TARGET_SIGCHLD: > > + case TARGET_SIGURG: > > + case TARGET_SIGWINCH: > > + case TARGET_SIGINFO: > > + /* Ignored by default. */ > > + return 0; > > + case TARGET_SIGCONT: > > + case TARGET_SIGSTOP: > > + case TARGET_SIGTSTP: > > + case TARGET_SIGTTIN: > > + case TARGET_SIGTTOU: > > + /* Job control signals. */ > > + return 0; > > + default: > > + return 1; > > + } > > +} > > + > > +static inline abi_ulong get_sigframe(struct target_sigaction *ka, > > + CPUArchState *regs, size_t frame_size) > > +{ > > + abi_ulong sp; > > + > > + /* Use default user stack */ > > + sp = get_sp_from_cpustate(regs); > > + > > + if ((ka->sa_flags & TARGET_SA_ONSTACK) && (sas_ss_flags(sp) == 0)) { > > + sp = target_sigaltstack_used.ss_sp + > > + target_sigaltstack_used.ss_size; > > + } > > + > > +#if defined(TARGET_MIPS) || defined(TARGET_ARM) > > + return (sp - frame_size) & ~7; > > +#elif defined(TARGET_AARCH64) > > + return (sp - frame_size) & ~15; > > +#else > > + return sp - frame_size; > > +#endif > > We don't need to do it in this patchseries, but you should strongly > consider pulling the architecture-specifics out in a way that > avoids this kind of ifdef ladder. > Totally agreed. I debated fixing this before I started this patch run, but I decided to pick my battles... I'll fix this in a follow up. > > +} > > + > > +/* compare to mips/mips/pm_machdep.c and sparc64/sparc64/machdep.c > sendsig() */ > Two dead architectures... I've updated the comments... and the filename which they live in... > > +static void setup_frame(int sig, int code, struct target_sigaction *ka, > > + target_sigset_t *set, target_siginfo_t *tinfo, CPUArchState *regs) > > +{ > > + struct target_sigframe *frame; > > + abi_ulong frame_addr; > > + int i; > > + > > + frame_addr = get_sigframe(ka, regs, sizeof(*frame)); > > + trace_user_setup_frame(regs, frame_addr); > > + if (!lock_user_struct(VERIFY_WRITE, frame, frame_addr, 0)) { > > + goto give_sigsegv; > > FreeBSD for Arm (haven't checked other BSDs or other archs) > gives a SIGILL for the "can't write signal frame to stack" > case, I think: > > https://github.com/freebsd/freebsd-src/blob/main/sys/arm/arm/exec_machdep.c#L316 > I don't understand why they picked SIGILL, SIGSEGV seems much more > logical to me, but we should follow the kernel behaviour. > This is a good thing to find. I'm going to have to study all the architectures, but the first 5 I looked at all returned SIGILL, so this code has to change to reflect that... > > + } > > + > > + memset(frame, 0, sizeof(*frame)); > > +#if defined(TARGET_MIPS) > > + int mflags = on_sig_stack(frame_addr) ? TARGET_MC_ADD_MAGIC : > > + TARGET_MC_SET_ONSTACK | TARGET_MC_ADD_MAGIC; > > +#else > > + int mflags = 0; > > +#endif > > + if (get_mcontext(regs, &frame->sf_uc.uc_mcontext, mflags)) { > > + goto give_sigsegv; > > The FreeBSD kernel get_mcontext() can't fail -- why can ours ? > (This matters because SIGSEGV may not be the right response to > whatever the failure case is.) > if (mcp->mc_vfp_size != 0 && mcp->mc_vfp_size != sizeof(target_mcontext_vfp_t)) { is what I try to validate, but looking at the kernel code it does NOT return vfp, so that check is bogus. I need to remove it (I'd added as part of a prior review without fully checking before I made the change, to be honest). > > + } > > + > > + for (i = 0; i < TARGET_NSIG_WORDS; i++) { > > + if (__put_user(set->__bits[i], > &frame->sf_uc.uc_sigmask.__bits[i])) { > > + goto give_sigsegv; > > __get_user() and __put_user() in QEMU can't fail, so you don't > need to check for errors here, unlike the non-double-underscore > versions. At some point you might want to take the current linux-user > versions of these user-access functions/macros: it looks like bsd-user > has an older version which doesn't handle the case where the guest > has looser alignment restrictions than the host. The new ones > actually expand to do { ... } while(0) statements which won't > be valid inside an if() condition. > OK. I'll make a sweep in addition to fixing this. > (Historical note: the reason QEMU's __put_user/__get_user ever had > return values at all is that the linux-user code was copy-and-pasted > from the Linux kernel. In the Linux kernel handling of writing > data to userspace is/was error-checked on every write, whereas > QEMU does the "is this writable" test once with the lock_user > function and then can assume all the writes to that area succeed. > But we still started with a lot of copy-pasted code that was doing > unnecessary checks on __put_user and __get_user return values. > FreeBSD seems to handle write-checking in yet a third way, by > assembling the struct in kernel-space and checking for writability > once at the end when it copies the whole block out to userspace.) > We're nothing if not creative... But this is old school Unix which started doing this in V7 which started doing it for stat and ftime system calls... > > + } > > + } > > + > > + if (tinfo) { > > + frame->sf_si.si_signo = tinfo->si_signo; > > + frame->sf_si.si_errno = tinfo->si_errno; > > + frame->sf_si.si_code = tinfo->si_code; > > + frame->sf_si.si_pid = tinfo->si_pid; > > + frame->sf_si.si_uid = tinfo->si_uid; > > + frame->sf_si.si_status = tinfo->si_status; > > + frame->sf_si.si_addr = tinfo->si_addr; > > + > > + if (TARGET_SIGILL == sig || TARGET_SIGFPE == sig || > > + TARGET_SIGSEGV == sig || TARGET_SIGBUS == sig || > > + TARGET_SIGTRAP == sig) { > > + frame->sf_si._reason._fault._trapno = > tinfo->_reason._fault._trapno; > > + } > > + > > + /* > > + * If si_code is one of SI_QUEUE, SI_TIMER, SI_ASYNCIO, or > > + * SI_MESGQ, then si_value contains the application-specified > > + * signal value. Otherwise, the contents of si_value are > > + * undefined. > > + */ > > + if (SI_QUEUE == code || SI_TIMER == code || SI_ASYNCIO == code > || > > + SI_MESGQ == code) { > > + frame->sf_si.si_value.sival_int = tinfo->si_value.sival_int; > > + } > > + > > + if (SI_TIMER == code) { > > + frame->sf_si._reason._timer._timerid = > > + tinfo->_reason._timer._timerid; > > + frame->sf_si._reason._timer._overrun = > > + tinfo->_reason._timer._overrun; > > + } > > + > > +#ifdef SIGPOLL > > + if (SIGPOLL == sig) { > > + frame->sf_si._reason._band = tinfo->_reason._band; > > + } > > +#endif > > This seems to be yet a third set of the logic for handling > target_siginfo_t's union, to go along with tswap_siginfo() and > host_to_target_siginfo_noswap(), except that the logic here is > different. linux-user calls tswap_siginfo() in its signal-frame > setup code. > Yea, I need to get that sorted out as well.. It's my biggest remaining item to resolve (except maybe for the comments for do_* you made, I've not yet completely digested them when I saw they were more than reviewed by). > > + > > + } > > + > > + if (set_sigtramp_args(regs, sig, frame, frame_addr, ka)) { > > + goto give_sigsegv; > > + } > > set_sigtramp_args() can't fail. (Not sure why it has a non-void > return type.) > OK. I'll fix this as well. > > + > > + unlock_user_struct(frame, frame_addr, 1); > > + return; > > + > > +give_sigsegv: > > + unlock_user_struct(frame, frame_addr, 1); > > + force_sig(TARGET_SIGSEGV); > > +} > > + > > void signal_init(void) > > { > > TaskState *ts = (TaskState *)thread_cpu->opaque; > > -- > > 2.33.1 > > thanks > No, thank you. This is quite helpful and got me to look at a number of new places and understand some historic background. Warmer -- PMM