x64: Fix ELF initial stack state

Fix ELF initial stack state as per Figure 3.9 ("Initial Process Stack") in the x86-64 ABI specification. This is needed for statically linked executables. Signed-off-by: Pekka Enberg <[email protected]>
cloudius-systems · Nov 18, 2014 · cdc758b · cdc758b
1 parent 463ca65
commit cdc758b
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Showing 4 changed files with 21 additions and 3 deletions.
diff --git a/arch/aarch64/arch-elf.hh b/arch/aarch64/arch-elf.hh
@@ -19,4 +19,10 @@ enum {
 /* for pltgot relocation */
 #define ARCH_JUMP_SLOT R_AARCH64_JUMP_SLOT
 
+inline void elf_entry_point(void* ep)
+{
+    // Not implemented:
+    assert(0);
+}
+
 #endif /* ARCH_ELF_HH */
diff --git a/arch/x64/arch-elf.hh b/arch/x64/arch-elf.hh
@@ -37,4 +37,16 @@ enum {
 /* for pltgot relocation */
 #define ARCH_JUMP_SLOT R_X86_64_JUMP_SLOT
 
+inline void elf_entry_point(void* ep)
+{
+    asm volatile (
+        "pushq $0\n\t" // Zero
+        "pushq $0\n\t" // Environment pointers
+        "pushq $0\n\t" // Zero
+        "pushq $0\n\t" // Argument count
+        "jmpq  *%0\n\t"
+        :
+        : "r"(ep));
+}
+
 #endif /* ARCH_ELF_HH */
diff --git a/core/app.cc b/core/app.cc
@@ -139,7 +139,7 @@ application::application(const std::string& command, const std::vector<std::stri
 
     _main = _lib->lookup<int (int, char**)>("main");
     if (!_main) {
-        _entry_point = reinterpret_cast<void(*)()>(_lib->entry_point());
+        _entry_point = _lib->entry_point();
     }
     if (!_entry_point && !_main) {
         throw launch_error("Failed looking up main");
@@ -202,7 +202,7 @@ void application::main()
         // may be called twice, TLS may be overriden and the program may not
         // received correct arguments, environment variables and auxiliary
         // vector.
-        _entry_point();
+        elf_entry_point(_entry_point);
     }
 
     // _entry_point() doesn't return

diff --git a/include/osv/app.hh b/include/osv/app.hh
@@ -154,7 +154,7 @@ private:
     mutex _termination_mutex;
     std::shared_ptr<elf::object> _lib;
     main_func_t* _main;
-    void (*_entry_point)();
+    void* _entry_point;
     static app_registry apps;
 
     // Must be destroyed before _lib