On 6/29/21 7:40 AM, Peter Maydell wrote:
On Fri, 18 Jun 2021 at 20:38, Richard Henderson <richard.hender...@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.hender...@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~
