Update x86_gcc.

send 16 bit aligned stack to callbacks.
Don´t include callback arguments in callback stack.
Update base pointe when switching stack.

Author: kristjanvalur

lib/sysv_i386/libstackman.a

@@ -30,21 +30,25 @@ stackman_switch:
 	movl	8(%ebp), %eax
 	movl	12(%ebp), %edx
 #APP
-# 48 "switch_x86_gcc.h" 1
-	subl $12, %esp
+# 50 "switch_x86_gcc.h" 1
+	subl $0x1a, %esp
 movl %eax, %esi
 movl %edx, %edi
-movl %esp, 8(%esp)
+leal 0x10(%esp), %ebx
+movl %ebx, 8(%esp)
 movl $0, 4(%esp)
 movl %edi, 0(%esp)
 call *%esi
-movl %eax, %esp
+leal -0x10(%eax), %esp
+subl %ebx, %eax
+addl %eax, %ebp
+leal 0x10(%esp), %eax
 movl %eax, 8(%esp)
 movl $1, 4(%esp)
 movl %edi, 0(%esp)
 call *%esi
 movl %eax, %eax
-addl $12, %esp
+addl $0x1a, %esp
 
 # 0 "" 2
 #NO_APP
@@ -75,16 +79,16 @@ stackman_call:
 	subl	$8, %esp
 	.cfi_offset 3, -12
 #APP
-# 96 "switch_x86_gcc.h" 1
+# 108 "switch_x86_gcc.h" 1
 	movl %esp, %ebx
 # 0 "" 2
-# 97 "switch_x86_gcc.h" 1
+# 109 "switch_x86_gcc.h" 1
 	movl %esp, %eax
 # 0 "" 2
 #NO_APP
 	movl	16(%ebp), %edx
 #APP
-# 100 "switch_x86_gcc.h" 1
+# 112 "switch_x86_gcc.h" 1
 	movl %edx, %esp
 # 0 "" 2
 #NO_APP
@@ -93,7 +97,7 @@ stackman_call:
 	pushl	12(%ebp)
 	call	*8(%ebp)
 #APP
-# 104 "switch_x86_gcc.h" 1
+# 116 "switch_x86_gcc.h" 1
 	movl %ebx, %esp
 # 0 "" 2
 #NO_APP
@@ -106,5 +110,5 @@ stackman_call:
 	.cfi_endproc
 .LFE1:
 	.size	stackman_call, .-stackman_call
-	.ident	"GCC: (Ubuntu 9.3.0-10ubuntu2) 9.3.0"
+	.ident	"GCC: (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0"
 	.section	.note.GNU-stack,"",@progbits

src/platforms/switch_x86_gcc.S

@@ -52,31 +52,41 @@ void *result;
       /* adjust stack pointer to be 16 byte (4 quad) aligned with 
        * room for call args
        * since the call instruction, 5 quads have
-       * been pushed (ip, bp, bx, si, di), need extra 3 quads
+       * been pushed (ip, bp, bx, si, di), need extra 3 quads (0xa)
        * for alignment, which fits our three quad call args.
+       * Add another 16 (0x10) bytes, so that we can pass to the callbacks
+       * a 16 byte boundary that lies above the pushed arguments
+       * so that the call arguments of the functions aren't clobbered
+       * by memory transfer.
        */
-    "subl $12, %%esp\n"
+    "subl $0x1a, %%esp\n"
     "movl %[cb], %%esi\n"  /* save 'callback' for later */
     "movl %[ctx], %%edi\n" /* save 'context' for later         */
 
-    /* first call */     
-    "movl %%esp, 8(%%esp)\n"  /* arg 2 sp */
+    /* first call */   
+    "leal 0x10(%%esp), %%ebx\n" /* arg 2 adjusted sp (also in nv. reg) */
+    "movl %%ebx, 8(%%esp)\n"
     "movl $0, 4(%%esp)\n"     /* arg 1 opcode STACKMAN_OP_SAVE */
     "movl %%edi, 0(%%esp)\n"  /* arg 0 context */
     "call *%%esi\n"
 
-    /* restore esp */
-    "movl %%eax, %%esp\n"
+    /* restore esp, re-adding shadow space */
+    "leal -0x10(%%eax), %%esp\n"
+    
+    /* and adjust ebp with difference between new and old */
+    "subl %%ebx, %%eax\n"
+    "addl %%eax, %%ebp\n"
 
     /* second call */
-    "movl %%eax, 8(%%esp)\n"  /* arg 2 sp */
+    "leal 0x10(%%esp), %%eax\n"  /* arg 2 sp */
+    "movl %%eax, 8(%%esp)\n"
     "movl $1, 4(%%esp)\n"     /* arg 1 opcode STACKMAN_OP_RESTORE */
     "movl %%edi, 0(%%esp)\n"  /* arg 0 context */
     "call *%%esi\n"
 
     "movl %%eax, %[result]\n"
 
-    "addl $12, %%esp\n"
+    "addl $0x1a, %%esp\n"
     : [result] "=r" (result)              /* output variables */
     : [cb] "r" (callback),       /* input variables  */
       [ctx] "r" (context)