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Merge pull request #256 from tkchia/tkchia/pid

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plat/msdos86: free up program memory above 64 KiB; also check we have enough memory for BSS
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David Given 2022-06-29 12:53:47 +02:00 committed by GitHub
parent df6cfe0410 1c71653d7f
commit 2c3c7a28e2
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GPG key ID: 4AEE18F83AFDEB23
2 changed files with 41 additions and 17 deletions
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54
plat/msdos86/boot.s
View file

@ -12,6 +12,8 @@
.sect .text
#define STACK_BUFFER 128 /* number of bytes to leave for stack */
begtext:
! Make sure we are running under MS-DOS 2 or above.
!
@ -20,9 +22,38 @@ begtext:
! segment. (DOS 3+ does; DOS 2.x does not.)
movb ah, 0x30
int 0x21
cbw
cmpb al, 2
xchg bx, ax
jc bad_sys
xchg bp, ax
jnc ok_sys
mov dx, bad_sys_msg
dos_msg:
movb ah, 9
int 0x21
ret
ok_sys:
! Resize the program's memory control block (MCB) to cover only the
! program's near code and data space. Use the starting sp value as
! a guide to how much memory we can grab. Abort on any failure.
!
! As a side effect, this also frees up any memory allocated to our
! program beyond 64 KiB. (The freed memory can possibly be used by
! e.g. child processes, in the future.)
!
! Also check that we have some space between the BSS end and the
! starting sp.
cmp sp, endbss+STACK_BUFFER
jb no_room
movb ah, 0x4a
mov bx, sp
movb cl, 4
shr bx, cl
inc bx
int 0x21
jc no_room
! Clear BSS.
mov di, begbss
@ -35,11 +66,12 @@ begtext:
! Get the size of the environment variables plus (if present) the
! program name. Also count the number of environment variables.
mov es, (0x002C)
xor di, di
mov es, 0x002C(di)
! ax = 0 from above
cwd ! dx = count of env. vars.
mov cx, -1
! cx = 0 from above
dec cx ! cx = max. str. bytes to scan
scasb ! handle special case of empty env.
jz is_empty_env
size_env:
@ -48,7 +80,7 @@ size_env:
scasb
jnz size_env
is_empty_env:
cmpb bl, 2
cmp bp, 2
jz no_argv0
scasw
repnz scasb
@ -58,10 +90,9 @@ no_argv0:
! onto the stack.
mov si, di
dec si
and si, -2
std
copy_env:
test si, si
and si, -2
eseg lodsw
push ax
jnz copy_env
@ -79,7 +110,7 @@ copy_env:
! Build up argc, argv[], and envp[].
push ax ! output buffer for argc, argv, envp
push bx ! MS-DOS version
push bp ! MS-DOS version
push cx ! env. string data
push dx ! count of env. vars.
mov ax, 0x0080
@ -97,13 +128,6 @@ copy_env:
push ax
call _exit
bad_sys:
mov dx, bad_sys_msg
dos_msg:
movb ah, 9
int 0x21
ret
no_room:
mov dx, no_room_msg
call dos_msg

4
plat/msdos86/libsys/sys_initmain.c
View file

@ -22,7 +22,7 @@ struct for_main {
* Return zero if everything went well, non-zero otherwise.
*/
int _sys_initmain(char *arg_data, size_t n_env_vars, char *env_data,
unsigned msdos_ver, struct for_main *out)
unsigned msdos_ver_major, struct for_main *out)
{
char **argv, **envp;
char c, *p, **pp;
@ -100,7 +100,7 @@ int _sys_initmain(char *arg_data, size_t n_env_vars, char *env_data,
* shortword) following the environment variables, so advance p by 3
* bytes to get at the program name.
*/
if ((msdos_ver & 0x00ff) >= 3)
if (msdos_ver_major >= 3)
{
p += 3;
argv[0] = p;