6153 - switch 'main' to use Mu strings

At the SubX level we have to put up with null-terminated kernel strings
for commandline args. But so far we haven't done much with them. Rather
than try to support them we'll just convert them transparently to standard
length-prefixed strings.

In the process I realized that it's not quite right to treat the combination
of argc and argv as an array of kernel strings. Argc counts the number
of elements, whereas the length of an array is usually denominated in bytes.

1 files changed, 89 insertions, 0 deletions

diff --git a/102kernel-string.subx b/102kernel-string.subx
new file mode 100644
index 00000000..ca92d813
--- /dev/null
+++ b/102kernel-string.subx
@@ -0,0 +1,89 @@
+# We can't really do much with null-terminated kernel strings, and we don't
+# want to. Let's turn them into regular length-prefixed strings at the first
+# opportunity.
+
+== code
+
+kernel-string-to-string:  # ad: (addr allocation-descriptor), in: (addr kernel-string) -> result/eax: (addr array byte)
+    # . prologue
+    55/push-ebp
+    89/<- %ebp 4/r32/esp
+    # . save registers
+    51/push-ecx
+    52/push-edx
+    53/push-ebx
+    56/push-esi
+    57/push-edi
+    # var len/ecx: int = length(in)
+    (kernel-string-length *(ebp+0xc))
+    89/<- %ecx 0/r32/eax
+    # result = allocate-array(ad, len)
+    (allocate-array *(ebp+8) %ecx)  # => eax
+    # var c/edx: byte = 0
+    ba/copy-to-edx 0/imm32
+    # var src/esi: (addr byte) = in
+    8b/-> *(ebp+0xc) 6/r32/esi
+    # var dest/edi: (addr byte) = result->data
+    8d/copy-address *(eax+4) 7/r32/edi
+    {
+$kernel-string-to-string:loop:
+      # c = *src
+      8a/byte-> *esi 2/r32/edx
+      # if (c == 0) break
+      81 7/subop/compare %edx 0/imm32
+      74/jump-if-= break/disp8
+      # *dest = c
+      88/byte<- *edi 2/r32/edx
+      # ++src
+      46/increment-esi
+      # ++dest
+      47/increment-edi
+      eb/jump loop/disp8
+    }
+$kernel-string-to-string:end:
+    # . restore registers
+    5f/pop-to-edi
+    5e/pop-to-esi
+    5b/pop-to-ebx
+    5a/pop-to-edx
+    59/pop-to-ecx
+    # . epilogue
+    89/<- %esp 5/r32/ebp
+    5d/pop-to-ebp
+    c3/return
+
+kernel-string-length:  # in: (addr kernel-string) -> result/eax: int
+    # . prologue
+    55/push-ebp
+    89/<- %ebp 4/r32/esp
+    # . save registers
+    51/push-ecx
+    52/push-edx
+    # result = 0
+    b8/copy-to-eax 0/imm32
+    # var c/ecx: byte = 0
+    b9/copy-to-ecx 0/imm32
+    # var curr/edx: (addr byte) = in
+    8b/-> *(ebp+8) 2/r32/edx
+    {
+$kernel-string-length:loop:
+      # c = *curr
+      8a/byte-> *edx 1/r32/ecx
+      # if (c == 0) break
+      81 7/subop/compare %ecx 0/imm32
+      74/jump-if-= break/disp8
+      # ++curr
+      42/increment-edx
+      # ++result
+      40/increment-eax
+      #
+      eb/jump loop/disp8
+    }
+$kernel-string-length:end:
+    # . restore registers
+    5a/pop-to-edx
+    59/pop-to-ecx
+    # . epilogue
+    89/<- %esp 5/r32/ebp
+    5d/pop-to-ebp
+    c3/return