| Message ID | 20210618192951.125651-11-richard.henderson@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | linux-user: Move signal trampolines to new page | expand |
On Fri, 18 Jun 2021 at 20:38, Richard Henderson <richard.henderson@linaro.org> wrote: > > Create and record the two signal trampolines. > Use them when the guest does not use SA_RESTORER. > Note that x86_64 does not use this code. > > Signed-off-by: Richard Henderson <richard.henderson@linaro.org> > --- > linux-user/i386/target_signal.h | 2 ++ > linux-user/x86_64/target_signal.h | 3 +++ > linux-user/i386/signal.c | 42 ++++++++++++++++++------------- > 3 files changed, 29 insertions(+), 18 deletions(-) > > diff --git a/linux-user/i386/target_signal.h b/linux-user/i386/target_signal.h > index 50361af874..64d09f2e75 100644 > --- a/linux-user/i386/target_signal.h > +++ b/linux-user/i386/target_signal.h > @@ -22,4 +22,6 @@ typedef struct target_sigaltstack { > #include "../generic/signal.h" > > #define TARGET_ARCH_HAS_SETUP_FRAME > +#define TARGET_ARCH_HAS_SIGTRAMP_PAGE 1 > + > #endif /* I386_TARGET_SIGNAL_H */ > diff --git a/linux-user/x86_64/target_signal.h b/linux-user/x86_64/target_signal.h > index 4ea74f20dd..4673c5a886 100644 > --- a/linux-user/x86_64/target_signal.h > +++ b/linux-user/x86_64/target_signal.h > @@ -21,4 +21,7 @@ typedef struct target_sigaltstack { > > #include "../generic/signal.h" > > +/* For x86_64, use of SA_RESTORER is mandatory. */ > +#define TARGET_ARCH_HAS_SIGTRAMP_PAGE 0 > + > #endif /* X86_64_TARGET_SIGNAL_H */ > diff --git a/linux-user/i386/signal.c b/linux-user/i386/signal.c > index 8701774e37..a83ecba54f 100644 > --- a/linux-user/i386/signal.c > +++ b/linux-user/i386/signal.c > @@ -337,16 +337,7 @@ void setup_frame(int sig, struct target_sigaction *ka, > if (ka->sa_flags & TARGET_SA_RESTORER) { > __put_user(ka->sa_restorer, &frame->pretcode); > } else { > - uint16_t val16; > - abi_ulong retcode_addr; > - retcode_addr = frame_addr + offsetof(struct sigframe, retcode); > - __put_user(retcode_addr, &frame->pretcode); > - /* This is popl %eax ; movl $,%eax ; int $0x80 */ > - val16 = 0xb858; > - __put_user(val16, (uint16_t *)(frame->retcode+0)); > - __put_user(TARGET_NR_sigreturn, (int *)(frame->retcode+2)); > - val16 = 0x80cd; > - __put_user(val16, (uint16_t *)(frame->retcode+6)); > + __put_user(default_sigreturn, &frame->pretcode); > In the kernel in arch/x86/kernel/signal.c there is a comment: /* * This is popl %eax ; movl $__NR_sigreturn, %eax ; int $0x80 * * WE DO NOT USE IT ANY MORE! It's only left here for historical * reasons and because gdb uses it as a signature to notice * signal handler stack frames. */ which suggests that we also should continue to fill in the retcode bytes in the signal frame for gdb's benefit even though we don't actually execute them any more. thanks -- PMM
On 6/29/21 7:40 AM, Peter Maydell wrote: > On Fri, 18 Jun 2021 at 20:38, Richard Henderson > <richard.henderson@linaro.org> wrote: >> >> Create and record the two signal trampolines. >> Use them when the guest does not use SA_RESTORER. >> Note that x86_64 does not use this code. >> >> Signed-off-by: Richard Henderson <richard.henderson@linaro.org> >> --- >> linux-user/i386/target_signal.h | 2 ++ >> linux-user/x86_64/target_signal.h | 3 +++ >> linux-user/i386/signal.c | 42 ++++++++++++++++++------------- >> 3 files changed, 29 insertions(+), 18 deletions(-) >> >> diff --git a/linux-user/i386/target_signal.h b/linux-user/i386/target_signal.h >> index 50361af874..64d09f2e75 100644 >> --- a/linux-user/i386/target_signal.h >> +++ b/linux-user/i386/target_signal.h >> @@ -22,4 +22,6 @@ typedef struct target_sigaltstack { >> #include "../generic/signal.h" >> >> #define TARGET_ARCH_HAS_SETUP_FRAME >> +#define TARGET_ARCH_HAS_SIGTRAMP_PAGE 1 >> + >> #endif /* I386_TARGET_SIGNAL_H */ >> diff --git a/linux-user/x86_64/target_signal.h b/linux-user/x86_64/target_signal.h >> index 4ea74f20dd..4673c5a886 100644 >> --- a/linux-user/x86_64/target_signal.h >> +++ b/linux-user/x86_64/target_signal.h >> @@ -21,4 +21,7 @@ typedef struct target_sigaltstack { >> >> #include "../generic/signal.h" >> >> +/* For x86_64, use of SA_RESTORER is mandatory. */ >> +#define TARGET_ARCH_HAS_SIGTRAMP_PAGE 0 >> + >> #endif /* X86_64_TARGET_SIGNAL_H */ >> diff --git a/linux-user/i386/signal.c b/linux-user/i386/signal.c >> index 8701774e37..a83ecba54f 100644 >> --- a/linux-user/i386/signal.c >> +++ b/linux-user/i386/signal.c >> @@ -337,16 +337,7 @@ void setup_frame(int sig, struct target_sigaction *ka, >> if (ka->sa_flags & TARGET_SA_RESTORER) { >> __put_user(ka->sa_restorer, &frame->pretcode); >> } else { >> - uint16_t val16; >> - abi_ulong retcode_addr; >> - retcode_addr = frame_addr + offsetof(struct sigframe, retcode); >> - __put_user(retcode_addr, &frame->pretcode); >> - /* This is popl %eax ; movl $,%eax ; int $0x80 */ >> - val16 = 0xb858; >> - __put_user(val16, (uint16_t *)(frame->retcode+0)); >> - __put_user(TARGET_NR_sigreturn, (int *)(frame->retcode+2)); >> - val16 = 0x80cd; >> - __put_user(val16, (uint16_t *)(frame->retcode+6)); >> + __put_user(default_sigreturn, &frame->pretcode); >> > > In the kernel in arch/x86/kernel/signal.c there is a comment: > > /* > * This is popl %eax ; movl $__NR_sigreturn, %eax ; int $0x80 > * > * WE DO NOT USE IT ANY MORE! It's only left here for historical > * reasons and because gdb uses it as a signature to notice > * signal handler stack frames. > */ > > which suggests that we also should continue to fill in the > retcode bytes in the signal frame for gdb's benefit even though > we don't actually execute them any more. Point. I noticed the same for several other targets, but didn't actually look at the kernel code for i386. r~
diff --git a/linux-user/i386/target_signal.h b/linux-user/i386/target_signal.h index 50361af874..64d09f2e75 100644 --- a/linux-user/i386/target_signal.h +++ b/linux-user/i386/target_signal.h @@ -22,4 +22,6 @@ typedef struct target_sigaltstack { #include "../generic/signal.h" #define TARGET_ARCH_HAS_SETUP_FRAME +#define TARGET_ARCH_HAS_SIGTRAMP_PAGE 1 + #endif /* I386_TARGET_SIGNAL_H */ diff --git a/linux-user/x86_64/target_signal.h b/linux-user/x86_64/target_signal.h index 4ea74f20dd..4673c5a886 100644 --- a/linux-user/x86_64/target_signal.h +++ b/linux-user/x86_64/target_signal.h @@ -21,4 +21,7 @@ typedef struct target_sigaltstack { #include "../generic/signal.h" +/* For x86_64, use of SA_RESTORER is mandatory. */ +#define TARGET_ARCH_HAS_SIGTRAMP_PAGE 0 + #endif /* X86_64_TARGET_SIGNAL_H */ diff --git a/linux-user/i386/signal.c b/linux-user/i386/signal.c index 8701774e37..a83ecba54f 100644 --- a/linux-user/i386/signal.c +++ b/linux-user/i386/signal.c @@ -337,16 +337,7 @@ void setup_frame(int sig, struct target_sigaction *ka, if (ka->sa_flags & TARGET_SA_RESTORER) { __put_user(ka->sa_restorer, &frame->pretcode); } else { - uint16_t val16; - abi_ulong retcode_addr; - retcode_addr = frame_addr + offsetof(struct sigframe, retcode); - __put_user(retcode_addr, &frame->pretcode); - /* This is popl %eax ; movl $,%eax ; int $0x80 */ - val16 = 0xb858; - __put_user(val16, (uint16_t *)(frame->retcode+0)); - __put_user(TARGET_NR_sigreturn, (int *)(frame->retcode+2)); - val16 = 0x80cd; - __put_user(val16, (uint16_t *)(frame->retcode+6)); + __put_user(default_sigreturn, &frame->pretcode); } /* Set up registers for signal handler */ @@ -415,14 +406,7 @@ void setup_rt_frame(int sig, struct target_sigaction *ka, if (ka->sa_flags & TARGET_SA_RESTORER) { __put_user(ka->sa_restorer, &frame->pretcode); } else { - uint16_t val16; - addr = frame_addr + offsetof(struct rt_sigframe, retcode); - __put_user(addr, &frame->pretcode); - /* This is movl $,%eax ; int $0x80 */ - __put_user(0xb8, (char *)(frame->retcode+0)); - __put_user(TARGET_NR_rt_sigreturn, (int *)(frame->retcode+1)); - val16 = 0x80cd; - __put_user(val16, (uint16_t *)(frame->retcode+5)); + __put_user(default_rt_sigreturn, &frame->pretcode); } #else /* XXX: Would be slightly better to return -EFAULT here if test fails @@ -591,3 +575,25 @@ badframe: force_sig(TARGET_SIGSEGV); return -TARGET_QEMU_ESIGRETURN; } + +#ifndef TARGET_X86_64 +void setup_sigtramp(abi_ulong sigtramp_page) +{ + uint16_t *tramp = lock_user(VERIFY_WRITE, sigtramp_page, 2 * 8, 0); + assert(tramp != NULL); + + default_sigreturn = sigtramp_page; + /* This is popl %eax ; movl $,%eax ; int $0x80 */ + __put_user(0xb858, (uint16_t *)(tramp + 0)); + __put_user(TARGET_NR_sigreturn, (int *)(tramp + 2)); + __put_user(0x80cd, (uint16_t *)(tramp + 6)); + + default_rt_sigreturn = sigtramp_page + 8; + /* This is movl $,%eax ; int $0x80 */ + __put_user(0xb8, (char *)(tramp + 8)); + __put_user(TARGET_NR_rt_sigreturn, (int *)(tramp + 9)); + __put_user(0x80cd, (uint16_t *)(tramp + 13)); + + unlock_user(tramp, sigtramp_page, 2 * 8); +} +#endif
Create and record the two signal trampolines. Use them when the guest does not use SA_RESTORER. Note that x86_64 does not use this code. Signed-off-by: Richard Henderson <richard.henderson@linaro.org> --- linux-user/i386/target_signal.h | 2 ++ linux-user/x86_64/target_signal.h | 3 +++ linux-user/i386/signal.c | 42 ++++++++++++++++++------------- 3 files changed, 29 insertions(+), 18 deletions(-) -- 2.25.1