libc: add tests and fix a bunch of bugs in string.s

libc/README.md

@@ -26,6 +26,4 @@ Somewhat nice implementations of:
 
 ## Correctness:
 
-This library is 100% untested. Feel free to report bugs using github issues. I'm sure ther are many. We are working on testing!
+This library is only lightly tested, so be careful and report bugs when you find them!
-
-

libc/stdlib.s

@@ -96,7 +96,11 @@ free:
 // s0 = &_atexit_count
 // s2 = &_atexit_calls
 // s1 = updated value of atexit
+// s3 = exit code
 exit:
+        // save exit code to s3
+        mv      s3, a0
+_exit_start:
         la      s0, _atexit_count       // s0 = &_atexit_count
         lw      s1, 0(s0)               // s1 = *(&_atexit_count)
         // exit if no atexit() calls remain
@@ -108,12 +112,12 @@ exit:
         li      s2, _atexit_calls
         add     s1, s1, s2              // s1 = &_atexit_calls + (s1)
         lw      s1, 0(s1)               // s1 = *s1
-        la      ra, exit                // set ra up to point to exit
+        la      ra, _exit_start         // set ra up to point to exit
         jalr    zero, s1, 0             // jump to address in s1
         // jalr will call the other function, which will then return back
         // to the beginning of exit.
 _exit:
-        li      a0, 0
+        mv      a0, s3
         li      a7, 93
         ecall
 

libc/string.s

@@ -3,8 +3,9 @@
 // Copyright (c) 2023 Anton Lydike
 // SPDX-License-Identifier: MIT
 
+// Create NullPtr constant
+.equ        NULL, 0x00
 .global     NULL
-// A global constant representing zero
 
 
 .global     strlen
@@ -35,13 +36,11 @@
 // copies the character c to the first n characters of  str.
 
 
+// missing implementations
 //.global     memcmp
 //.global     memcpy
 //.global     strcat
 
-// Create NullPtr constant
-.set        NULL, 0x00
-
 
 .text
 strlen:
@@ -101,7 +100,7 @@ __strncpy_end:
 
 
 strcpy:
-// char *strncpy(char *dest, const char *src)
+// char *strcpy(char *dest, const char *src)
             sw   s1, sp, -4     // push s1 to the stack
             sw   s2, sp, -8     // push s1 to the stack
             add  s1, a0, zero   // save dest pointer for return
@@ -124,15 +123,16 @@ __strcpy_loop:
 memchr:
 // void *memchr(const void *str, char c, size_t n)
             sw   s1, sp, -4     // push s1 to the stack
+            andi a1, a1, 0xff   // trim a1 to be byte-sized
 __memchr_loop:
             beq  a2, zero, __memchr_ret_null
             lb   s1, a0, 0
             addi a0, a0, 1  // let a0 point to the next byte
             addi a2, a2, -1 // decrement bytes to copy by 1
-            bne  s1, s2, __memchr_loop
+            bne  s1, a1, __memchr_loop
             // return pointer to prev byte (as the prev byte actually matched a1)
             addi a0, a0, -1
-            // pop s1, s2 from stack
+            // pop s1, from stack
             lw   s1, sp, -4
             ret
 __memchr_ret_null:

test/filecheck/libc/test-string.s

@@ -0,0 +1,114 @@
+// RUN: python3 -m riscemu -v %s libc/string.s libc/stdlib.s libc/crt0.s | filecheck %s
+
+.data
+
+data:
+.byte       0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88
+.byte       0x99, 0xAA, 0xBB, 0xCC, 0xDD, 0xEE, 0xFF, 0x00
+
+dest:
+.byte       0xAB, 0xAB, 0xAB, 0xAB, 0xAB, 0xAB, 0xAB, 0xAB
+.byte       0xAB, 0xAB, 0xAB, 0xAB, 0xAB, 0xAB, 0xAB, 0xAB
+
+small_str:
+.string     "test"
+
+.text
+
+.globl      main
+main:
+// test that strlen(data) == 15
+        addi    sp, sp, -4
+        sw      ra, 0(sp)
+        la      a0, data
+        // call strlen(data)
+        jal     strlen
+        li      t0, 15
+        bne     a0, t0, _fail
+
+// now memcpy strlen(data)+1 bytes from data to dest
+        la      a0, dest
+        la      a1, data
+        li      a2, 16
+        // call strncpy(dest, data, 16)
+        jal     strncpy
+        la      a1, dest
+        // fail because strncpy should return pointer to dest
+        bne     a0, a1, _fail
+        // check that dest and data are the same
+        jal     check_data_dest_is_same
+        la      a0, dest
+        li      a1, 0x11
+        li      a2, 16
+// test that memset(dest) workds
+        // call memset(dest, 0x11, 16)
+        jal     memset
+        // check that all of dest is 0x11111111
+        li      t1, 0x11111111
+        la      a0, dest
+        lw      t0, 0(a0)
+        bne     t0, t1, _fail
+        lw      t0, 1(a0)
+        bne     t0, t1, _fail
+        lw      t0, 2(a0)
+        bne     t0, t1, _fail
+        lw      t0, 3(a0)
+        bne     t0, t1, _fail
+// test memchr
+        // test memchr
+        la      a0, data
+        li      a1, 0x55
+        li      a2, 16
+        // memchr(data, 0x55, 16)
+        jal     memchr
+        la      t0, data
+        addi    t0, t0, 4
+        // fail if a0 != data+4
+        bne     a0, t0, _fail
+        la      a0, data
+        li      a1, 0x12
+        li      a2, 16
+        // memchr(data, 0x12, 16)
+        jal     memchr
+        // check that result is NULL
+        bne     a0, zero, _fail
+// test strcpy
+        la      a0, dest
+        la      a1, small_str
+        // call strcpy(dest, small_str)
+        jal     strcpy
+        la      t0, dest
+        lw      t1, 0(a0)
+        // ascii for "tset", as risc-v is little endian
+        li      t2, 0x74736574
+        bne     t1, t2, _fail
+
+// return to exit() wrapper
+        lw      ra, 0(sp)
+        addi    sp, sp, 4
+        li      a0, 0
+        ret
+
+_fail:
+        ebreak
+        // fail the test run
+        li      a0, -1
+        jal     exit
+
+
+check_data_dest_is_same:
+        la      a0, data
+        la      a1, dest
+        li      a2, 4
+1:
+        lw      t0, 0(a0)
+        lw      t1, 0(a1)
+        bne     t0, t1, _fail
+        addi    a0, a0, 4
+        addi    a1, a1, 4
+        addi    a2, a2, -1
+        blt     zero, a2, 1b
+        ret
+
+
+//CHECK: [CPU] Program exited with code 0

test/filecheck/lit.cfg

@@ -6,4 +6,4 @@ xdsl_src = os.path.dirname(os.path.dirname(config.test_source_root))
 
 config.name = "riscemu"
 config.test_format = lit.formats.ShTest(preamble_commands=[f"cd {xdsl_src}"])
-config.suffixes = ['.asm']
+config.suffixes = ['.asm', '.s']