vm/c-debugger: Quash registers on syscall

This makes the debugger reset registers to bogus values on all syscalls.
The last few tests that were not working under it are now fixed.

The entire bootstrap process now preserves registers when making
syscalls. This will make it possible to implement syscalls as ordinary
functions in the Onramp OS. It also makes it possible to proxy syscalls
by child processes in the libc.

Author: ludocode

core/libc/0-oo/src/stdio.oo

@@ -370,8 +370,10 @@
     7E 00 &__fopen_not_append   ; jz 0 &__fopen_not_append
 
     ; mode is append. seek to the end
-    70 81 00 FF     ; add r1 0 -1     ; mov r1 -1
-    70 82 00 FF     ; add r2 0 -1     ; mov r2 -1
+    ; TODO probably remove this, I don't think append is used in bootstrapping.
+    70 81 00 02     ; add r1 0 2     ; mov r1 2
+    70 82 00 00     ; add r2 0 0     ; mov r2 0
+    70 83 00 00     ; add r3 0 0     ; mov r3 0
     7F 07 00 00     ; sys fseek 0 0
     ;78 82 8D F4     ; ldw r2 rfp -12
     ;79 80 82 04     ; stw 0 r2 4      ; position in file

platform/vm/c-debugger/src/vm.c

@@ -923,6 +923,12 @@ static void vm_sys(vm_t* vm, uint8_t syscall_number, uint8_t arg1, uint8_t arg2)
     }
 
     vm->registers[0] = ret;
+
+    // We quash all other caller-preserved registers to ensure that programs do
+    // not depend on register preservation.
+    for (size_t i = 1; i <= 0xB; ++i) {
+        vm->registers[i] = 0xDEADDEAD;
+    }
 }
 
 #if 0

test/as/0-basic/tests/hello-world.oo

@@ -3,20 +3,13 @@
 
 
 
-
-
-
 =main 
-7C80<__process_info_table 
-7C80>__process_info_table 
-78808E80
-
-
-70898000
 
 
-708A8910
-78808A00
+7C89<__process_info_table 
+7C89>__process_info_table 
+78898E89
+78808910
 
 
 7C81<hello_world 
@@ -26,8 +19,10 @@
 7F060000
 
 
-708A8908
-788A8A00
+7C89<__process_info_table 
+7C89>__process_info_table 
+78898E89
+788A8908
 
 
 70800000

test/as/0-basic/tests/hello-world.os

@@ -2,21 +2,14 @@
 ; Copyright (c) 2023-2024 Fraser Heavy Software
 ; This test case is part of the Onramp compiler project.
 
-; TODO this was written before we were linking against libc, hack to workaround it
-;=_start
-;    ; format indicator
-;    "~Onr~amp~   "
+; TODO this was written before we were linking against libc. it makes direct syscalls.
 =main
-ims r0 <__process_info_table
-ims r0 >__process_info_table
-ldw r0 rpp r0
-
-    ; store process info table in r9
-    add r9 r0 '00
 
     ; get the output file descriptor
-    add ra r9 '10
-    ldw r0 ra '00
+    ims r9 <__process_info_table
+    ims r9 >__process_info_table
+    ldw r9 rpp r9
+    ldw r0 r9 '10
 
     ; write(stdout, "Hello world!", 12)
     ims r1 <hello_world
@@ -26,8 +19,10 @@ ldw r0 rpp r0
     sys fwrite '00 '00
 
     ; get the exit address
-    add ra r9 '08
-    ldw ra ra '00
+    ims r9 <__process_info_table
+    ims r9 >__process_info_table
+    ldw r9 rpp r9
+    ldw ra r9 '08
 
     ; exit(0)
     add r0 '00 '00   ; set exit parameter to 0 (success)

test/ld/1-omc/programs/eight-queens.oe

@@ -53,7 +53,7 @@
     78 8D 00 8C     ; ldw rfp 0 rsp     ; pop rfp
     70 8C 8C 04     ; add rsp rsp 4     ; ^^^
     70 80 00 00     ; add r0 0 0        ; zero r0
-    78 8F 89 08     ; ldw rip r9 8      ; ret
+    78 8F 00 8C     ; ldw rip 0 rsp     ; ret
 
 
 

test/ld/1-omc/programs/eight-queens.oo

@@ -8,11 +8,12 @@
     7E 61 6D 70   ; jz 97 28781
     7E 20 20 20   ; jz 32 8224
 
-    ; store process info vector in r9
-    70 89 80 00   ; add r9 r0 0
+    ; push process info vector
+    71 8C 8C 04   ; sub rsp rsp 4
+    79 80 8C 00   ; stw r0 rsp 0
 
     ; get the output file descriptor
-    70 8A 89 10   ; add ra r9 16  (output stream handle)
+    70 8A 80 10   ; add ra r0 16  (output stream handle)
     78 80 8A 00   ; ldw r0 ra 0
 
     ; output("Hello world!")
@@ -21,6 +22,7 @@
     7F 06 00 00   ; sys write 0 0
 
     ; get the exit address
+    78 89 8C 00   ; ldw r9 rsp 0
     70 8A 89 08   ; add ra r9 8  (exit address)
     78 8A 8A 00   ; ldw ra ra 0
 
@@ -29,7 +31,6 @@
     70 8F 8A 00   ; add rip ra 0      ; jump to exit address
 
     ; padding
-    00 00 00 00 00 00 00 00
     00 00 00 00
 
 @0x40 =hello_world

test/vm/files/fseek.skip

@@ -24,6 +24,8 @@
 # If a corresponding .env file exists, the contents are passed as environment
 # variables to the program. Otherwise, the program inherits the current
 # environment.
+#
+# If a corresponding .skip file exists, the test is skipped.
 
 if [ "$1" == "" ]; then
     echo "Need command to test."
@@ -49,6 +51,12 @@ echo "Running vm tests on: $COMMAND"
 for HEXNAME in $(find $(dirname $0)/* -name '*.oe.ohx'); do
     THIS_ERROR=0
     BASENAME=$(echo $HEXNAME|sed 's/\.oe\.ohx$//')
+
+    if [ -e $BASENAME.skip ]; then
+        echo "Skipping $BASENAME"
+        continue
+    fi
+
     echo "Testing $BASENAME"
 
     ARGS=