[PATCH v2 0/2] MR2921: winebuild: Simplify some assembly in the 16-bit support routines.

[Zebediah Figura (＠zfigura)]

--
  v2: winebuild: Use the lretw mnemonic in wine_call_to_16().
      winebuild: Use segment prefixes in 16-bit stack switching code instead of writing out byte values.

https://gitlab.winehq.org/wine/wine/-/merge_requests/2921

[PATCH v2 1/2] winebuild: Use segment prefixes in 16-bit stack switching code instead of writing out byte values.

[Zebediah Figura]

From: Zebediah Figura

Presumably at one point there were assemblers that choked on these. However, currently we use segment prefixes elsewhere in wine (namely, in the syscall dispatcher), and it seems fair to assume that a sane compiler should support them.
---
 tools/winebuild/relay.c | 60 ++++++++++++++++++++---------------------
 1 file changed, 30 insertions(+), 30 deletions(-)

diff --git a/tools/winebuild/relay.c b/tools/winebuild/relay.c
index b86a88aae24..c14a3a70b17 100644
--- a/tools/winebuild/relay.c
+++ b/tools/winebuild/relay.c
@@ -134,10 +134,10 @@ static void BuildCallFrom16Core( int reg_func, int thunk )
     {
         output( "\tcall 1f\n" );
         output( "1:\tpopl %%ecx\n" );
-        output( "\t.byte 0x2e\n\tmovl %s-1b(%%ecx),%%edx\n", asm_name("CallTo16_DataSelector") );
+        output( "\tmovl %%cs:%s-1b(%%ecx),%%edx\n", asm_name("CallTo16_DataSelector") );
     }
     else
-        output( "\t.byte 0x2e\n\tmovl %s,%%edx\n", asm_name("CallTo16_DataSelector") );
+        output( "\tmovl %%cs:%s,%%edx\n", asm_name("CallTo16_DataSelector") );

/* Load 32-bit segment registers */
     output( "\tmovw %%dx, %%ds\n" );
@@ -148,7 +148,7 @@ static void BuildCallFrom16Core( int reg_func, int thunk )
     else
         output( "\tmovw %s, %%fs\n", asm_name("CallTo16_TebSelector") );

-    output( "\t.byte 0x64\n\tmov (%d),%%gs\n", GS_OFFSET );
+    output( "\tmov %%fs:(%d),%%gs\n", GS_OFFSET );

/* Translate STACK16FRAME base to flat offset in %edx */
     output( "\tmovw %%ss, %%dx\n" );
@@ -166,12 +166,12 @@ static void BuildCallFrom16Core( int reg_func, int thunk )
     if (reg_func) output( "\tpopl %%ecx\n" );

/* Get the 32-bit stack pointer from the TEB and complete STACK16FRAME */
-    output( "\t.byte 0x64\n\tmovl (%d), %%ebp\n", STACKOFFSET );
+    output( "\tmovl %%fs:(%d), %%ebp\n", STACKOFFSET );
     output( "\tpushl %%ebp\n" );

/* Switch stacks */
-    output( "\t.byte 0x64\n\tmovw %%ss, (%d)\n", STACKOFFSET + 2 );
-    output( "\t.byte 0x64\n\tmovw %%sp, (%d)\n", STACKOFFSET );
+    output( "\tmovw %%ss, %%fs:(%d)\n", STACKOFFSET + 2 );
+    output( "\tmovw %%sp, %%fs:(%d)\n", STACKOFFSET );
     output( "\tpushl %%ds\n" );
     output( "\tpopl %%ss\n" );
     output( "\tmovl %%ebp, %%esp\n" );
@@ -198,9 +198,9 @@ static void BuildCallFrom16Core( int reg_func, int thunk )
         output( "\tcall *0x26(%%edx)\n");  /* FIELD_OFFSET(STACK16FRAME,entry_point) */

/* Switch stack back */
-        output( "\t.byte 0x64\n\tmovw (%d), %%ss\n", STACKOFFSET+2 );
-        output( "\t.byte 0x64\n\tmovzwl (%d), %%esp\n", STACKOFFSET );
-        output( "\t.byte 0x64\n\tpopl (%d)\n", STACKOFFSET );
+        output( "\tmovw %%fs:(%d), %%ss\n", STACKOFFSET+2 );
+        output( "\tmovzwl %%fs:(%d), %%esp\n", STACKOFFSET );
+        output( "\tpopl %%fs:(%d)\n", STACKOFFSET );

/* Restore registers and return directly to caller */
         output( "\taddl $8, %%esp\n" );
@@ -257,9 +257,9 @@ static void BuildCallFrom16Core( int reg_func, int thunk )
         output( "\tmovzwl 0x2c(%%edx),%%eax\n"); /* FIELD_OFFSET(STACK16FRAME,ip) */
         output( "\tmovl %%eax,0xb8(%%esp)\n" );  /* Eip */

-        output( "\t.byte 0x64\n\tmovzwl (%d), %%eax\n", STACKOFFSET+2 );
+        output( "\tmovzwl %%fs:(%d), %%eax\n", STACKOFFSET+2 );
         output( "\tmovl %%eax,0xc8(%%esp)\n" );  /* SegSs */
-        output( "\t.byte 0x64\n\tmovzwl (%d), %%eax\n", STACKOFFSET );
+        output( "\tmovzwl %%fs:(%d), %%eax\n", STACKOFFSET );
         output( "\taddl $0x2c,%%eax\n");         /* FIELD_OFFSET(STACK16FRAME,ip) */
         output( "\tmovl %%eax,0xc4(%%esp)\n" );  /* Esp */
 #if 0
@@ -290,9 +290,9 @@ static void BuildCallFrom16Core( int reg_func, int thunk )
         output( "\tleal -748(%%ebp),%%ebx\n" ); /* sizeof(CONTEXT) + FIELD_OFFSET(STACK32FRAME,ebp) */

/* Switch stack back */
-        output( "\t.byte 0x64\n\tmovw (%d), %%ss\n", STACKOFFSET+2 );
-        output( "\t.byte 0x64\n\tmovzwl (%d), %%esp\n", STACKOFFSET );
-        output( "\t.byte 0x64\n\tpopl (%d)\n", STACKOFFSET );
+        output( "\tmovw %%fs:(%d), %%ss\n", STACKOFFSET+2 );
+        output( "\tmovzwl %%fs:(%d), %%esp\n", STACKOFFSET );
+        output( "\tpopl %%fs:(%d)\n", STACKOFFSET );

/* Get return address to CallFrom16 stub */
         output( "\taddw $0x14,%%sp\n" ); /* FIELD_OFFSET(STACK16FRAME,callfrom_ip)-4 */
@@ -335,9 +335,9 @@ static void BuildCallFrom16Core( int reg_func, int thunk )
     else
     {
         /* Switch stack back */
-        output( "\t.byte 0x64\n\tmovw (%d), %%ss\n", STACKOFFSET+2 );
-        output( "\t.byte 0x64\n\tmovzwl (%d), %%esp\n", STACKOFFSET );
-        output( "\t.byte 0x64\n\tpopl (%d)\n", STACKOFFSET );
+        output( "\tmovw %%fs:(%d), %%ss\n", STACKOFFSET+2 );
+        output( "\tmovzwl %%fs:(%d), %%esp\n", STACKOFFSET );
+        output( "\tpopl %%fs:(%d)\n", STACKOFFSET );

/* Restore registers */
         output( "\tpopl %%edx\n" );
@@ -398,22 +398,22 @@ static void BuildCallTo16Core( int reg_func )
     output_cfi( ".cfi_rel_offset %%esi,-8" );
     output( "\tpushl %%edi\n" );
     output_cfi( ".cfi_rel_offset %%edi,-12" );
-    output( "\t.byte 0x64\n\tmov %%gs,(%d)\n", GS_OFFSET );
+    output( "\tmov %%gs,%%fs:(%d)\n", GS_OFFSET );

/* Setup exception frame */
-    output( "\t.byte 0x64\n\tpushl (%d)\n", STACKOFFSET );
+    output( "\tpushl %%fs:(%d)\n", STACKOFFSET );
     output( "\tpushl 16(%%ebp)\n" ); /* handler */
-    output( "\t.byte 0x64\n\tpushl (0)\n" );
-    output( "\t.byte 0x64\n\tmovl %%esp,(0)\n" );
+    output( "\tpushl %%fs:(0)\n" );
+    output( "\tmovl %%esp,%%fs:(0)\n" );

/* Call the actual CallTo16 routine (simulate a lcall) */
     output( "\tpushl %%cs\n" );
     output( "\tcall .L%s\n", name );

/* Remove exception frame */
-    output( "\t.byte 0x64\n\tpopl (0)\n" );
+    output( "\tpopl %%fs:(0)\n" );
     output( "\taddl $4, %%esp\n" );
-    output( "\t.byte 0x64\n\tpopl (%d)\n", STACKOFFSET );
+    output( "\tpopl %%fs:(%d)\n", STACKOFFSET );

if ( !reg_func )
     {
@@ -468,9 +468,9 @@ static void BuildCallTo16Core( int reg_func )

/* Switch to the 16-bit stack */
     output( "\tmovl %%esp,%%edx\n" );
-    output( "\t.byte 0x64\n\tmovw (%d),%%ss\n", STACKOFFSET + 2);
-    output( "\t.byte 0x64\n\tmovw (%d),%%sp\n", STACKOFFSET );
-    output( "\t.byte 0x64\n\tmovl %%edx,(%d)\n", STACKOFFSET );
+    output( "\tmovw %%fs:(%d),%%ss\n", STACKOFFSET + 2);
+    output( "\tmovw %%fs:(%d),%%sp\n", STACKOFFSET );
+    output( "\tmovl %%edx,%%fs:(%d)\n", STACKOFFSET );

/* Make %bp point to the previous stackframe (built by CallFrom16) */
     output( "\tmovzwl %%sp,%%ebp\n" );
@@ -541,20 +541,20 @@ static void BuildRet16Func(void)

/* Restore 32-bit segment registers */

-    output( "\t.byte 0x2e\n\tmovl %s", asm_name("CallTo16_DataSelector") );
+    output( "\tmovl %%cs:%s", asm_name("CallTo16_DataSelector") );
     output( "-%s,%%edi\n", asm_name("__wine_call16_start") );
     output( "\tmovw %%di,%%ds\n" );
     output( "\tmovw %%di,%%es\n" );

-    output( "\t.byte 0x2e\n\tmov %s", asm_name("CallTo16_TebSelector") );
+    output( "\tmov %%cs:%s", asm_name("CallTo16_TebSelector") );
     output( "-%s,%%fs\n", asm_name("__wine_call16_start") );

-    output( "\t.byte 0x64\n\tmov (%d),%%gs\n", GS_OFFSET );
+    output( "\tmov %%fs:(%d),%%gs\n", GS_OFFSET );

/* Restore the 32-bit stack */

output( "\tmovw %%di,%%ss\n" );
-    output( "\t.byte 0x64\n\tmovl (%d),%%esp\n", STACKOFFSET );
+    output( "\tmovl %%fs:(%d),%%esp\n", STACKOFFSET );

/* Return to caller */

[PATCH v2 2/2] winebuild: Use the lretw mnemonic in wine_call_to_16().

[Zebediah Figura]

From: Zebediah Figura

We already use it in the __wine_spec_callfrom16_* functions.
---
 tools/winebuild/relay.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/tools/winebuild/relay.c b/tools/winebuild/relay.c
index c14a3a70b17..d06be8fc371 100644
--- a/tools/winebuild/relay.c
+++ b/tools/winebuild/relay.c
@@ -519,8 +519,7 @@ static void BuildCallTo16Core( int reg_func )
     }

/* Jump to the called routine */
-    output( "\t.byte 0x66\n" );
-    output( "\tlret\n" );
+    output( "\tlretw\n" );

/* Function footer */
     output_function_size( func_name );

[Zebediah Figura (＠zfigura)]

> > We always compile i386 code without PIC in Wine
>
> That's only true on Linux, this will break other platforms like Android.

I see, I was not aware that we were still compiling some platforms with -fPIC. I've removed that commit, it's not really a blocker, just something that seemed like a nice simplification.