[PATCH v2 03/33] linux-user/x86_64: Allocate vsyscall page as a commpage

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

We're about to start validating PAGE_EXEC, which means that we've
got to the vsyscall page executable.  We had been special casing
this entirely within translate.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 linux-user/elfload.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 29d910c4cc..d783240a36 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -195,6 +195,28 @@ static void elf_core_copy_regs(target_elf_gregset_t *regs, const CPUX86State *en
     (*regs)[26] = tswapreg(env->segs[R_GS].selector & 0xffff);
 }
 
+#if ULONG_MAX >= TARGET_VSYSCALL_PAGE
+#define HI_COMMPAGE  TARGET_VSYSCALL_PAGE
+
+static bool init_guest_commpage(void)
+{
+    /*
+     * The vsyscall page is at a high negative address aka kernel space,
+     * which means that we cannot actually allocate it with target_mmap.
+     * We still should be able to use page_set_flags, unless the user
+     * has specified -R reserved_va, which would trigger an assert().
+     */
+    if (reserved_va != 0 &&
+        TARGET_VSYSCALL_PAGE + TARGET_PAGE_SIZE >= reserved_va) {
+        error_report("Cannot allocate vsyscall page");
+        exit(EXIT_FAILURE);
+    }
+    page_set_flags(TARGET_VSYSCALL_PAGE,
+                   TARGET_VSYSCALL_PAGE + TARGET_PAGE_SIZE,
+                   PAGE_EXEC | PAGE_VALID);
+    return true;
+}
+#endif
 #else
 
 #define ELF_START_MMAP 0x80000000
-- 
2.34.1