fix(templates): avoid clobbering ebx in su_load_gmdls

Fixes #130

CHANGELOG.md

@@ -7,6 +7,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ### Added
 - Dbgain unit, which allows defining the gain in decibels (-40 dB to +40dB)
 
+### Fixed
+- 32-bit su_load_gmdls clobbered ebx, even though __stdcall demands it to be not
+  touched
+
 ## v0.3.0
 ### Added
 - Scroll bars to menus, shown when a menu is too long to fit.

vm/compiler/templates/amd64-386/gmdls.asm

@@ -23,15 +23,17 @@
     add     rsp, 40         ; shadow space, as required by Win64 ABI
     ret
 {{else}}
-    mov     ebx, su_sample_table
-    push    0                   ; OF_READ
-    push    ebx                 ; &ofstruct, blatantly reuse the sample table
-    push    su_gmdls_path1      ; path
-    call    dword [__imp__OpenFile@12]; eax = OpenFile(path,&ofstruct,OF_READ) // should not touch ebx according to calling convention
+    mov     eax, su_sample_table
+    ; these are the arguments for ReadFile
     push    0                       ; NULL
-    push    ebx                     ; &bytes_read, reusing sample table again; it does not matter that the first four bytes are trashed
+    push    eax                     ; &bytes_read, reusing sample table again; it does not matter that the first four bytes are trashed
     push    3440660                 ; number of bytes to read
-    push    ebx                     ; here we actually pass the sample table to readfile
+    push    eax                     ; here we actually pass the sample table to readfile
+    ; these are for OpenFile
+    push    0                   ; OF_READ
+    push    eax                 ; &ofstruct, blatantly reuse the sample table
+    push    su_gmdls_path1      ; path
+    call    dword [__imp__OpenFile@12]; eax = OpenFile(path,&ofstruct,OF_READ)
     push    eax                     ; handle to file
     call    dword [__imp__ReadFile@20] ; Readfile(handle,&su_sample_table,SAMPLE_TABLE_SIZE,&bytes_read,NULL)
     ret