Allocate DPMI host memory in UMB if possible

This may save a few KBs (up to 8?) of conventional memory.
alexfru · Apr 13, 2024 · 287c313 · 287c313
1 parent f946f35
commit 287c313
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Showing 7 changed files with 56 additions and 12 deletions.
diff --git a/v0100/bindp/n2f.exe b/v0100/bindp/n2f.exe
diff --git a/v0100/bindp/smlrc.exe b/v0100/bindp/smlrc.exe
diff --git a/v0100/bindp/smlrcc.exe b/v0100/bindp/smlrcc.exe
diff --git a/v0100/bindp/smlrl.exe b/v0100/bindp/smlrl.exe
diff --git a/v0100/bindp/smlrpp.exe b/v0100/bindp/smlrpp.exe
diff --git a/v0100/lib/dpstub.exe b/v0100/lib/dpstub.exe
diff --git a/v0100/srclib/dpstub.asm b/v0100/srclib/dpstub.asm
@@ -154,12 +154,14 @@ cpu 386
  ; TBD??? additional stub info & a.out header validation?
 
  ; allocate memory for the DPMI host
+ call link_umb
  mov bx, [pm_entry_sz]
  or bx, 1
  mov ah, 0x48
  int 0x21
- jc err_nomem
  mov [pm_entry_seg], ax
+ call restore_umb ; N.B. preserves flags
+ jc err_nomem
 
  ; enter 32-bit protected mode
  mov es, [pm_entry_seg]
@@ -360,6 +362,44 @@ check_dos3:
  push ax
  retf
 
+link_umb:
+ cmp word [dos_ver], 0x500
+ jc .done ; fail if DOS prior to 5.0
+
+ mov ax, 0x5800
+ int 0x21
+ mov [orig_alloc_strategy], al
+ mov ax, 0x5802
+ int 0x21
+ mov [orig_umb_linked], al
+
+ mov ax, 0x5803
+ mov bx, 0x0001 ; link UMB for allocations
+ int 0x21
+ mov ax, 0x5801
+ mov bx, 0x0080 ; first fit strategy: first try it in UMB, last in conventional mem
+ ; N.B. 0x0081=best fit strategy doesn't seem to work as expected at least on DOSBox
+ int 0x21
+.done:
+ ret
+
+restore_umb:
+ pushf ; preserve flags to simplify error checking
+ cmp word [dos_ver], 0x500
+ jc .done ; fail if DOS prior to 5.0
+
+ mov ax, 0x5803
+ mov bl, [orig_umb_linked]
+ xor bh, bh
+ int 0x21
+ mov ax, 0x5801
+ mov bl, [orig_alloc_strategy]
+ xor bh, bh
+ int 0x21
+.done:
+ popf
+ ret
+
 dpmi_detect:
  mov ax, 0x1687
  int 0x2f
@@ -555,6 +595,7 @@ exec:
  push si
  push di
  push bp
+ call link_umb ; loading CWSDPMI while UMB is linked saves most conventional memory
  mov word [exec_params_env_seg], 0
  mov word [exec_params_params + 0], exec_args
  mov word [exec_params_params + 2], ds
@@ -574,6 +615,7 @@ exec:
  mov ss, [cs:save_ss]
  mov sp, [cs:save_sp]
  sti
+ call restore_umb ; N.B. preserves flags
  sbb ax, ax ; ax = 0 (and zf = 1) IFF success
  jnz exec_end
  mov ah, 0x4d
@@ -891,20 +933,22 @@ align 16
 
 section .bss ; Note, we aren't zeroing .bss!
 
-cs_seg resw 1
-ds_seg resw 1
-psp_seg resw 1
-dos_ver resw 1
-env_seg resw 1
-path_ofs resw 1
+cs_seg resw 1
+ds_seg resw 1
+psp_seg resw 1
+dos_ver resw 1
+orig_alloc_strategy resb 1
+orig_umb_linked resb 1
+env_seg resw 1
+path_ofs resw 1
 
-exit_sp resw 1
+exit_sp  resw 1
 
-argv0 resb 81 ; shared with 32-bit code
+argv0  resb 81 ; shared with 32-bit code
 
-pm_entry resd 1
-pm_entry_sz resw 1
-pm_entry_seg resw 1
+pm_entry  resd 1
+pm_entry_sz  resw 1
+pm_entry_seg  resw 1
 
 exec_params:
 exec_params_env_seg resw 1