Changeset 96568 in vbox

Timestamp:

Sep 1, 2022 8:26:32 PM (2 years ago)

Author:

vboxsync

Message:

IPRT/nocrt: Fixed alloca_probe/chkstk issue where it would partly trash the saved register values. bugref:10261

File:

• trunk/src/VBox/Runtime/common/compiler/vcc/stack-vcc.asm (modified) (5 diffs)

trunk/src/VBox/Runtime/common/compiler/vcc/stack-vcc.asm

@@ -124 +124 @@
 ;
 ; @param    xAX     Frame size.
-; @uses     AMD64: Nothing (because we don't quite now the convention).
-;           x86:   ESP = ESP - EAX; nothing else
+; @uses     AMD64:  Probably nothing. EAX is certainly not supposed to change.
+;           x86:    ESP = ESP - EAX; EFLAGS, nothing else
 ;
 ALIGNCODE(64)
@@ -141 +141 @@
 
         ;
-        ; Adjust eax so we can use xBP for stack addressing.
-        ;
-        sub     xAX, xCB*2
-        jle     .touch_loop_done
+        ; Adjust eax so we're relative to [xBP - xCB*2].
+        ;
+        sub     xAX, xCB * 4
+        jle     .touch_loop_done            ; jump if rax < xCB*4, very unlikely
 
         ;
@@ -150 +150 @@
         ; the touch loop if (int)xAX > 0.
         ;
-        mov     ebx, PAGE_SIZE - 1
-        and     ebx, ebp
+        lea     ebx, [ebp - xCB * 2]
+        and     ebx, PAGE_SIZE - 1
         sub     xAX, xBX
-        jnl     .touch_loop
+        jnl     .touch_loop                 ; jump if pages to touch.
 
 .touch_loop_done:
@@ -167 +167 @@
         sub     esp, eax
         add     esp, 4
-        jmp    dword [esp + eax - 4]
+        jmp     dword [esp + eax - 4]
 %endif
 
@@ -175 +175 @@
 .touch_loop:
         sub     xBX, PAGE_SIZE
-        mov     [xBP + xBX], bl
+%if 1
+        mov     [xBP + xBX - xCB * 2], bl
+%else
+        or      byte [xBP + xBX - xCB * 2], 0   ; non-destructive variant...
+%endif
         sub     xAX, PAGE_SIZE
         jnl     .touch_loop