[PATCH 01/21] linux-user: Add infrastructure for a signal trampoline page

[Richard Henderson <richard.henderson@linaro.org>]

Allocate a page to hold the signal trampoline(s).
Invoke a guest-specific hook to fill in the contents
of the page before marking it read-execute again.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 linux-user/qemu.h    |  7 +++++++
 linux-user/elfload.c | 17 +++++++++++++++++
 linux-user/signal.c  |  3 +++
 3 files changed, 27 insertions(+)

diff --git a/linux-user/qemu.h b/linux-user/qemu.h
index 3b0b6b75fe..9e5e2aa499 100644
--- a/linux-user/qemu.h
+++ b/linux-user/qemu.h
@@ -437,6 +437,13 @@ abi_long do_sigaltstack(abi_ulong uss_addr, abi_ulong uoss_addr,
 int do_sigprocmask(int how, const sigset_t *set, sigset_t *oldset);
 abi_long do_swapcontext(CPUArchState *env, abi_ulong uold_ctx,
                         abi_ulong unew_ctx, abi_long ctx_size);
+
+/* Fallback addresses into sigtramp page. */
+extern abi_ulong default_sigreturn;
+extern abi_ulong default_rt_sigreturn;
+
+void setup_sigtramp(abi_ulong tramp_page);
+
 /**
  * block_signals: block all signals while handling this guest syscall
  *
diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 17ab06f612..7bc67ac9cb 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -14,6 +14,7 @@
 #include "qemu/units.h"
 #include "qemu/selfmap.h"
 #include "qapi/error.h"
+#include "target_signal.h"
 
 #ifdef _ARCH_PPC64
 #undef ARCH_DLINFO
@@ -25,6 +26,10 @@
 #undef ELF_ARCH
 #endif
 
+#ifndef TARGET_ARCH_HAS_SIGTRAMP_PAGE
+#define TARGET_ARCH_HAS_SIGTRAMP_PAGE 0
+#endif
+
 #define ELF_OSABI   ELFOSABI_SYSV
 
 /* from personality.h */
@@ -3232,6 +3237,18 @@ int load_elf_binary(struct linux_binprm *bprm, struct image_info *info)
 #endif
     }
 
+    /*
+     * TODO: load a vdso, which would also contain the signal trampolines.
+     * Otherwise, allocate a private page to hold them.
+     */
+    if (TARGET_ARCH_HAS_SIGTRAMP_PAGE) {
+        abi_ulong tramp_page = target_mmap(0, TARGET_PAGE_SIZE,
+                                           PROT_READ | PROT_WRITE,
+                                           MAP_PRIVATE | MAP_ANON, -1, 0);
+        setup_sigtramp(tramp_page);
+        target_mprotect(tramp_page, TARGET_PAGE_SIZE, PROT_READ | PROT_EXEC);
+    }
+
     bprm->p = create_elf_tables(bprm->p, bprm->argc, bprm->envc, &elf_ex,
                                 info, (elf_interpreter ? &interp_info : NULL));
     info->start_stack = bprm->p;
diff --git a/linux-user/signal.c b/linux-user/signal.c
index 9016896dcd..2f19cc0bf6 100644
--- a/linux-user/signal.c
+++ b/linux-user/signal.c
@@ -30,6 +30,9 @@ static struct target_sigaction sigact_table[TARGET_NSIG];
 static void host_signal_handler(int host_signum, siginfo_t *info,
                                 void *puc);
 
+/* Fallback addresses into sigtramp page. */
+abi_ulong default_sigreturn;
+abi_ulong default_rt_sigreturn;
 
 /*
  * System includes define _NSIG as SIGRTMAX + 1,
-- 
2.25.1