Parse procedure parameters

1 files changed, 65 insertions, 1 deletions

diff --git a/boot/symbol.s b/boot/symbol.s
index 66409aa..a927b0e 100644
--- a/boot/symbol.s
+++ b/boot/symbol.s
@@ -2,7 +2,7 @@
 # v. 2.0. If a copy of the MPL was not distributed with this file, You can
 # obtain one at https://mozilla.org/MPL/2.0/.
 
-.global symbol_table_build
+.global symbol_table_build, symbol_table_find
 
 .include "boot/definitions.inc"
 
@@ -49,6 +49,70 @@ symbol_table: .zero SYMBOL_PRIME
 
 .section .text
 
+# Searches for a symbol by name.
+#
+# Parameters:
+# a0 - Local symbol table or 0.
+# a1 - Length of the symbol to search.
+# a2 - Pointer to the symbol name.
+#
+# Sets a0 to the symbol info.
+.type symbol_table_find, @function
+symbol_table_find:
+	# Prologue.
+	addi sp, sp, -32
+	sw ra, 28(sp)
+	sw s0, 24(sp)
+	addi s0, sp, 32
+
+	sw s1, 20(sp) # Current symbol in the table.
+	sw s2, 16(sp) # Symbol table length.
+	sw s3, 12(sp) # Length of the symbol to search.
+	sw s4, 8(sp) # Pointer to the symbol to search.
+
+	mv s3, a1
+	mv s4, a2
+
+	la s1, symbol_table
+	lw s2, 0(s1)
+	addi s1, s1, 4 # Advance to the first symbol in the table.
+
+.Lsymbol_table_find_loop:
+	beqz s2, .Lsymbol_table_find_not_found
+
+	# Compare string lengths.
+	lw a2, 0(s1)
+	bne s3, a2, .Lsymbol_table_find_continue
+
+	# If lengths match, compare the content.
+	mv a0, s4
+	lw a1, 4(s1)
+	call _memcmp
+
+	bnez a0, .Lsymbol_table_find_continue
+
+	lw a0, 8(s1) # Pointer to the symbol.
+	j .Lsymbol_table_end
+
+.Lsymbol_table_find_continue:
+	addi s2, s2, -1
+	j .Lsymbol_table_find_loop
+
+.Lsymbol_table_find_not_found:
+	li a0, 0
+
+.Lsymbol_table_end:
+	lw s1, 20(sp)
+	lw s2, 16(sp)
+	lw s3, 12(sp)
+	lw s4, 8(sp)
+
+	# Epilogue.
+	lw ra, 28(sp)
+	lw s0, 24(sp)
+	addi sp, sp, 32
+	ret
+
 # Build the initial symbols.
 #
 # Sets a0 to the pointer to the global symbol table.