Alexandre Julliard : ntdll: Allocate a 32-bit %fs selector on Linux in Wow64 mode.

[Alexandre Julliard]

Module: wine
Branch: master
Commit: a7b6b4f0d06127526addc4dba7c0b6b09821542b
URL:    https://source.winehq.org/git/wine.git/?a=commit;h=a7b6b4f0d06127526addc4dba...

Author: Alexandre Julliard <julliard(a)winehq.org>
Date:   Tue Jul  6 12:38:07 2021 +0200

ntdll: Allocate a 32-bit %fs selector on Linux in Wow64 mode.

Signed-off-by: Alexandre Julliard <julliard(a)winehq.org>

---

 dlls/ntdll/unix/signal_x86_64.c | 37 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/dlls/ntdll/unix/signal_x86_64.c b/dlls/ntdll/unix/signal_x86_64.c
index 6175bb9b230..b94ad9c4d91 100644
--- a/dlls/ntdll/unix/signal_x86_64.c
+++ b/dlls/ntdll/unix/signal_x86_64.c
@@ -88,6 +88,30 @@ WINE_DEFAULT_DEBUG_CHANNEL(seh);
 #include <asm/prctl.h>
 static inline int arch_prctl( int func, void *ptr ) { return syscall( __NR_arch_prctl, func, ptr ); }
 
+extern int CDECL alloc_fs_sel( int sel, void *base );
+__ASM_GLOBAL_FUNC( alloc_fs_sel,
+                   /* switch to 32-bit stack */
+                   "pushq %rbx\n\t"
+                   "pushq %rdi\n\t"
+                   "movq %rsp,%rdi\n\t"
+                   "movq %gs:0x8,%rsp\n\t"    /* NtCurrentTeb()->Tib.StackBase */
+                   "subl $0x10,%esp\n\t"
+                   /* setup modify_ldt struct on 32-bit stack */
+                   "movl %ecx,(%rsp)\n\t"     /* entry_number */
+                   "movl %edx,4(%rsp)\n\t"    /* base */
+                   "movl $~0,8(%rsp)\n\t"     /* limit */
+                   "movl $0x41,12(%rsp)\n\t"  /* seg_32bit | usable */
+                   /* invoke 32-bit syscall */
+                   "movl %esp,%ebx\n\t"
+                   "movl $0xf3,%eax\n\t"      /* SYS_set_thread_area */
+                   "int $0x80\n\t"
+                   /* restore stack */
+                   "movl (%rsp),%eax\n\t"     /* entry_number */
+                   "movq %rdi,%rsp\n\t"
+                   "popq %rdi\n\t"
+                   "popq %rbx\n\t"
+                   "ret" );
+
 #ifndef FP_XSTATE_MAGIC1
 #define FP_XSTATE_MAGIC1 0x46505853
 #endif
@@ -367,6 +391,7 @@ static inline void context_init_xstate( CONTEXT *context, void *xstate_buffer )
 static USHORT cs32_sel;  /* selector for %cs in 32-bit mode */
 static USHORT cs64_sel;  /* selector for %cs in 64-bit mode */
 static USHORT ds64_sel;  /* selector for %ds/%es/%ss in 64-bit mode */
+static USHORT fs32_sel;  /* selector for %fs in 32-bit mode */
 
 /***********************************************************************
  * Definitions for Dwarf unwind tables
@@ -1911,7 +1936,7 @@ NTSTATUS set_thread_wow64_context( HANDLE handle, const void *ctx, ULONG size )
     {
         wow_frame->SegDs = ds64_sel;
         wow_frame->SegEs = ds64_sel;
-        wow_frame->SegFs = 0;  /* FIXME */
+        wow_frame->SegFs = fs32_sel;
         wow_frame->SegGs = ds64_sel;
     }
     if (flags & CONTEXT_I386_DEBUG_REGISTERS)
@@ -2743,6 +2768,7 @@ void signal_init_thread( TEB *teb )
 #if defined __linux__
     arch_prctl( ARCH_SET_GS, teb );
     arch_prctl( ARCH_GET_FS, &amd64_thread_data()->pthread_teb );
+    if (fs32_sel) alloc_fs_sel( fs32_sel >> 3, (char *)teb + teb->WowTebOffset );
 #elif defined (__FreeBSD__) || defined (__FreeBSD_kernel__)
     amd64_set_gsbase( teb );
 #elif defined(__NetBSD__)
@@ -2793,7 +2819,15 @@ void signal_init_process(void)
 #ifdef __linux__
     if (NtCurrentTeb()->WowTebOffset)
     {
+        void *teb32 = (char *)NtCurrentTeb() + NtCurrentTeb()->WowTebOffset;
+        int sel;
+
         cs32_sel = 0x23;
+        if ((sel = alloc_fs_sel( -1, teb32 )) != -1)
+        {
+            fs32_sel = (sel << 3) | 3;
+        }
+        else ERR( "failed to allocate %%fs selector\n" );
     }
 #endif
 
@@ -2842,6 +2876,7 @@ void DECLSPEC_HIDDEN call_init_thunk( LPTHREAD_START_ROUTINE entry, void *arg, B
     context.SegCs  = cs64_sel;
     context.SegDs  = ds64_sel;
     context.SegEs  = ds64_sel;
+    context.SegFs  = fs32_sel;
     context.SegGs  = ds64_sel;
     context.SegSs  = ds64_sel;
     context.EFlags = 0x200;