linux-user/i386: Implement setup_sigtramp

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.

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210929130553.121567-11-richard.henderson@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

3 files changed, 43 insertions, 18 deletions

diff --git a/linux-user/i386/signal.c b/linux-user/i386/signal.c
index 3b4b55fc0a..b38b5f108e 100644
--- a/linux-user/i386/signal.c
+++ b/linux-user/i386/signal.c
@@ -310,6 +310,22 @@ get_sigframe(struct target_sigaction *ka, CPUX86State *env, size_t frame_size)
 }
 
 #ifndef TARGET_X86_64
+static void install_sigtramp(void *tramp)
+{
+    /* This is popl %eax ; movl $syscall,%eax ; int $0x80 */
+    __put_user(0xb858, (uint16_t *)(tramp + 0));
+    __put_user(TARGET_NR_sigreturn, (int32_t *)(tramp + 2));
+    __put_user(0x80cd, (uint16_t *)(tramp + 6));
+}
+
+static void install_rt_sigtramp(void *tramp)
+{
+    /* This is movl $syscall,%eax ; int $0x80 */
+    __put_user(0xb8, (uint8_t *)(tramp + 0));
+    __put_user(TARGET_NR_rt_sigreturn, (int32_t *)(tramp + 1));
+    __put_user(0x80cd, (uint16_t *)(tramp + 5));
+}
+
 /* compare linux/arch/i386/kernel/signal.c:setup_frame() */
 void setup_frame(int sig, struct target_sigaction *ka,
                  target_sigset_t *set, CPUX86State *env)
@@ -338,16 +354,9 @@ 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));
+        /* This is no longer used, but is retained for ABI compatibility. */
+        install_sigtramp(frame->retcode);
+        __put_user(default_sigreturn, &frame->pretcode);
     }
 
     /* Set up registers for signal handler */
@@ -416,14 +425,9 @@ 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));
+        /* This is no longer used, but is retained for ABI compatibility. */
+        install_rt_sigtramp(frame->retcode);
+        __put_user(default_rt_sigreturn, &frame->pretcode);
     }
 #else
     /* XXX: Would be slightly better to return -EFAULT here if test fails
@@ -592,3 +596,19 @@ 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;
+    install_sigtramp(tramp);
+
+    default_rt_sigreturn = sigtramp_page + 8;
+    install_rt_sigtramp(tramp + 8);
+
+    unlock_user(tramp, sigtramp_page, 2 * 8);
+}
+#endif
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 */