From 7648b5a7b22ae3b3e3a3fa39fd83bce06554385d Mon Sep 17 00:00:00 2001
From: turret <turret@duck.com>
Date: Mon, 18 Dec 2023 18:40:19 -0600
Subject: init: minor optimisations

move spin locks to dedicated function so we can minimise repetition of
code. now uses more C and less assembly.

init.c uses 8192 * 512 as a maximum even if the stack rlimit is larger
---
 init/init.c |  3 ++-
 init/log.c  | 34 +++++++++++++++++++++-------------
 2 files changed, 23 insertions(+), 14 deletions(-)

(limited to 'init')

diff --git a/init/init.c b/init/init.c
index e2ece8a..806792f 100644
--- a/init/init.c
+++ b/init/init.c
@@ -1,6 +1,7 @@
 #include <signal.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/param.h>
 #include <sys/resource.h>
 #include <sys/wait.h>
 
@@ -71,7 +72,7 @@ int main(void)
     struct rlimit *stack_rlimit = malloc(sizeof(struct rlimit));
     getrlimit(RLIMIT_STACK, stack_rlimit);
     if(stack_rlimit->rlim_cur != RLIM_INFINITY) {
-        stack_size = stack_rlimit->rlim_cur;
+        stack_size = MIN(stack_rlimit->rlim_cur, stack_size);
     }
     free(stack_rlimit);
 
diff --git a/init/log.c b/init/log.c
index 75840a2..2df6d82 100644
--- a/init/log.c
+++ b/init/log.c
@@ -32,7 +32,23 @@ static const char *mode_to_string[] = {
     [PANICMODE_DIE] = "catastrophic failure",
 };
 
-int console_lock = 0;
+static int console_lock = 0;
+
+static void obtain_console_lock()
+{
+    register int rax asm("rax");
+retry:
+    while(console_lock)
+        ;
+
+    asm("mov %0, 1\n\t"
+        "xchg %0, %1" : "=r" (rax) : "m" (console_lock));
+
+    if(rax)
+        goto retry;
+
+    return;
+}
 
 static int vaprint(const char *fmt, va_list ap)
 {
@@ -80,13 +96,9 @@ static int vaprint(const char *fmt, va_list ap)
        at the same time. I considered simply writing all at once, but
        ended up just not caring enough to the point where spinlocks
        prevail. */
-    if(dolocks) {
-        __asm__(".spin_lock:");
-        __asm__("mov rax, 1");
-        __asm__("xchg rax, [console_lock]");
-        __asm__("test rax, rax");
-        __asm__("jnz .spin_lock");
-    }
+    if(dolocks)
+        obtain_console_lock();
+
 
     /* we want to support stuff without colons, but frankly I havent
        tested this at time of writing. will find out later */
@@ -137,11 +149,7 @@ void _panic(const char *fileorigin,
     char **backtrace_symbolnames =
         backtrace_symbols(backtrace_addresses, backtrace_count);
 
-    __asm__("_panic.spin_lock:");
-    __asm__("mov rax, 1");
-    __asm__("xchg rax, [console_lock]");
-    __asm__("test rax, rax");
-    __asm__("jnz .spin_lock");
+    obtain_console_lock();
 
     print(NOLOCK("5") "------------[ cut here ]------------");
     print(LOG_SOH "\7""0"  "%s at %s:%d", mode_to_string[(int)mode],
-- 
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