From 4197ee0a928bd84e123734a87b1b755b86b9d1f8 Mon Sep 17 00:00:00 2001
From: Andreas Baumann <mail@andreasbaumann.cc>
Date: Mon, 3 Aug 2020 21:40:37 +0200
Subject: some work on noreturn and exit/Halt

---
 ecomp-c/asm-i386.c            |  4 ++--
 ecomp-c/build.sh              |  4 +++-
 ecomp-c/builtin_unreachable.c |  8 ++++++++
 ecomp-c/ec.c                  |  2 +-
 ecomp-c/libc-freestanding.c   | 17 +++++++++++++++--
 5 files changed, 29 insertions(+), 6 deletions(-)
 create mode 100644 ecomp-c/builtin_unreachable.c

diff --git a/ecomp-c/asm-i386.c b/ecomp-c/asm-i386.c
index 83904c5..9b303c8 100644
--- a/ecomp-c/asm-i386.c
+++ b/ecomp-c/asm-i386.c
@@ -146,12 +146,12 @@ static void Err( char *s, va_list args )
 	fflush( stderr );
 }
 
-static void Halt( int code )
+__attribute__((noreturn)) static void Halt( int code )
 {
 	exit( code );
 }
 
-static void Abort( char *s, ... )
+__attribute__((noreturn)) static void Abort( char *s, ... )
 {
 	va_list args;
 	va_start( args, s );
diff --git a/ecomp-c/build.sh b/ecomp-c/build.sh
index 1fce90b..1d7551e 100755
--- a/ecomp-c/build.sh
+++ b/ecomp-c/build.sh
@@ -13,7 +13,7 @@ MODULES+=("$BINARY.c")
 
 case "${COMPILER}" in
 	gcc)
-		CFLAGS="-m32 -march=i386 -Werror -Wno-noreturn -Wall -pedantic -std=c89 -x c"
+		CFLAGS="-m32 -march=i386 -Wall -pedantic -Werror -std=c89 -x c"
 		;;
 	clang)
 		CFLAGS="-m32 -march=i386 -Werror -Wall -pedantic -std=c89 -x c"
@@ -62,10 +62,12 @@ case "${COMPILER}:${MODE}" in
 		;;
 	pcc:freestanding)
 		CFLAGS+=" -ffreestanding -nostdlib -Wl,-emain"
+		MODULES+=("builtin_unreachable.c")
 		;;
 	tcc:freestanding)
 		CFLAGS+=" -fno-bultin -nostdlib"
 		MODULES+=("_start-stub.c")
+		MODULES+=("builtin_unreachable.c")
 		;;
 	*:hosted)
 		CFLAGS+=" -lbsd"
diff --git a/ecomp-c/builtin_unreachable.c b/ecomp-c/builtin_unreachable.c
new file mode 100644
index 0000000..4ba239e
--- /dev/null
+++ b/ecomp-c/builtin_unreachable.c
@@ -0,0 +1,8 @@
+/*
+ * __builtin_unreachable for pcc/tcc marking exit in
+ * libc-freestanding.c syscall1noret
+ */
+
+void __builtin_unreachable( void )
+{
+}
diff --git a/ecomp-c/ec.c b/ecomp-c/ec.c
index bc0944e..82775e0 100644
--- a/ecomp-c/ec.c
+++ b/ecomp-c/ec.c
@@ -133,7 +133,7 @@ static void Err( char *s, va_list args )
 	fflush( stderr );
 }
 
-static void Halt( int code )
+__attribute__((noreturn)) static void Halt( int code )
 {
 	exit( code );
 }
diff --git a/ecomp-c/libc-freestanding.c b/ecomp-c/libc-freestanding.c
index f37aa83..35f2e02 100644
--- a/ecomp-c/libc-freestanding.c
+++ b/ecomp-c/libc-freestanding.c
@@ -138,6 +138,19 @@ static __attribute__((noinline)) int syscall1( int id, int arg0 )
 	return retval;
 }
 
+void __builtin_unreachable( void );
+
+static __attribute__((noinline)) __attribute__((noreturn)) void syscall1noret( int id, int arg0 )
+{
+	__asm__ volatile( "\
+		push %%ebx\n\
+		mov %0, %%eax\n\
+		mov %1, %%ebx\n\
+		int $0x80\n\
+		pop %%ebx\n" : : "m"( id ), "m"( arg0 ) );
+	__builtin_unreachable( );
+}
+
 static __attribute__((noinline)) int syscall3( int id, int arg0, int arg1, int arg2 )
 {
 	int retval;
@@ -164,9 +177,9 @@ static __attribute__((noinline)) int syscall3( int id, int arg0, int arg1, int a
 	return retval;
 }
 
-void exit( int status )
+__attribute__((noreturn)) void exit( int status )
 {
-	syscall1( SYSCALL_EXIT, status );
+	syscall1noret( SYSCALL_EXIT, status );
 }
 
 static void strreverse( char *s )
-- 
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