LibC: Implement setjmp and longjmp for riscv64

The assembly implementation is based on the x86_64 version.

Userland/Libraries/LibC/arch/riscv64/setjmp.S

@@ -1,20 +1,91 @@
+/*
+ * Copyright (c) 2024, Sönke Holz <sholz8530@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <bits/sighow.h>
+
+//
+// /!\ Read setjmp.h before modifying this file!
+//
+
+#define DID_SAVE_SIGNAL_MASK_SLOT (14 * 8)
+#define SAVED_SIGNAL_MASK_SLOT    (14 * 8 + 4)
+
+// https://pubs.opengroup.org/onlinepubs/9699919799/functions/setjmp.html
+// int setjmp(jmp_buf env)
+// int _setjmp(jmp_buf env)
 .global _setjmp
 .global setjmp
 _setjmp:
 setjmp:
-    # FIXME: Implement setjmp.
+    li a1, 0                             // Set savemask argument to 0
-    unimp
 
+// https://pubs.opengroup.org/onlinepubs/9699919799/functions/sigsetjmp.html
+// int sigsetjmp(sigjmp_buf env, int savemask)
+.global sigsetjmp
+sigsetjmp:
+    sw a1, DID_SAVE_SIGNAL_MASK_SLOT(a0) // Store savemask into did_save_signal_mask
+    sw zero, SAVED_SIGNAL_MASK_SLOT(a0)  // Clear saved_signal_mask
+    beqz a1, .Lsaveregs
+
+    addi sp, sp, -16                     // Prepare ABI-compliant call to sigprocmask
+    sd a0, 0(sp)
+    sd ra, 8(sp)
+
+    li a0, 0                             // Set argument how
+    li a1, 0                             // Set argument set
+    addi a2, a0, SAVED_SIGNAL_MASK_SLOT  // Set argument oldset
+    call sigprocmask@plt
+
+    ld ra, 8(sp)
+    ld a0, 0(sp)
+    addi sp, sp, 16
+
+.Lsaveregs:
+    sd s0, 0*8(a0)                       // Save registers
+    sd s1, 1*8(a0)
+    sd s2, 2*8(a0)
+    sd s3, 3*8(a0)
+    sd s4, 4*8(a0)
+    sd s5, 5*8(a0)
+    sd s6, 6*8(a0)
+    sd s7, 7*8(a0)
+    sd s8, 8*8(a0)
+    sd s9, 9*8(a0)
+    sd s10, 10*8(a0)
+    sd s11, 11*8(a0)
+    sd sp, 12*8(a0)
+    sd ra, 13*8(a0)
+
+    li a0, 0
+    ret
+
+// https://pubs.opengroup.org/onlinepubs/9699919799/functions/longjmp.html
+// void longjmp(jmp_buf env, int val)
+// void _longjmp(jmp_buf env, int val)
 .global _longjmp
 .global longjmp
 _longjmp:
 longjmp:
-    # FIXME: Implement longjmp.
+    ld s0, 0*8(a0)                       // Restore registers
-    unimp
+    ld s1, 1*8(a0)
+    ld s2, 2*8(a0)
+    ld s3, 3*8(a0)
+    ld s4, 4*8(a0)
+    ld s5, 5*8(a0)
+    ld s6, 6*8(a0)
+    ld s7, 7*8(a0)
+    ld s8, 8*8(a0)
+    ld s9, 9*8(a0)
+    ld s10, 10*8(a0)
+    ld s11, 11*8(a0)
+    ld sp, 12*8(a0)
+    ld ra, 13*8(a0)
 
-.global _sigsetjmp
+    mv a0, a1
-.global sigsetjmp
+    bnez a0, .Lnonzero
-_sigsetjmp:
+    li a0, 1
-sigsetjmp:
+.Lnonzero:
-    # FIXME: Implement sigsetjmp.
+    ret
-    unimp

Userland/Libraries/LibC/setjmp.h

@@ -32,10 +32,9 @@ struct __jmp_buf {
     // FIXME: This is likely incorrect.
     uint64_t regs[22];
 #elif defined(__riscv) && __riscv_xlen == 64
-    // FIXME: This is likely incorrect.
     uint64_t s[12];
     uint64_t sp;
-    uint64_t pc;
+    uint64_t ra;
 #else
 #    error "Unknown architecture"
 #endif