sel4: add patch for sel4/syscalls.h

repos/base-sel4/doc/notes.txt

@@ -777,6 +777,19 @@ compiling position-independent code (as is the case for Genode). For now,
 we have are not compiling with '-fPIC' enabled but this issue is clear
 in front of us.
 
+Patches for the seL4 code will be reside at _base-sel4/src/kernel/_. E.g.,
+we just added the current modification of the _syscalls.h_ header by
+copying a git diff to the file _base-sel4/src/kernel/syscalls.patch_.
+To apply the patch automatically when preparing the seL4 port, we need
+to modify the _base-sel4/ports/sel4.port_ file by adding the following
+lines:
+
+! PATCHES   := src/kernel/syscalls.patch
+! PATCH_OPT := -p1 -d src/kernel/sel4
+
+Since we modified the port-description file, we need to update the
+accompanied hash via './tool/ports/update_hash sel4'.
+
 Anyway, after all the steps, our test-sel4 program can be successfully
 built. Executing the run script produces the result that we longed for:
 

repos/base-sel4/ports/sel4.hash

@@ -1 +1 @@
-c538b91d215024f21be14837192141004c9e3561
+39b692f97c6a83fdc35e22909b80ce804cc3aa84

repos/base-sel4/ports/sel4.port

@@ -6,3 +6,6 @@ URL(sel4) := https://github.com/seL4/seL4.git
 # experimental branch
 REV(sel4) := b6fbb78cb1233aa8549ea3acb90524306f49a8d2
 DIR(sel4) := src/kernel/sel4
+
+PATCHES   := src/kernel/syscalls.patch
+PATCH_OPT := -p1 -d src/kernel/sel4

repos/base-sel4/src/kernel/syscalls.patch

@@ -0,0 +1,13 @@
+diff --git a/libsel4/arch_include/ia32/sel4/arch/syscalls.h b/libsel4/arch_include/ia32/sel4/arch/syscalls.h
+index aef583b..d550343 100644
+--- a/libsel4/arch_include/ia32/sel4/arch/syscalls.h
++++ b/libsel4/arch_include/ia32/sel4/arch/syscalls.h
+@@ -475,7 +475,7 @@ seL4_DebugPutChar(char c)
+         "sysenter          \n"
+         "popl %%ebp        \n"
+         :
+-        : "a" (seL4_SysDebugPutChar),
++        : "a" ((int)seL4_SysDebugPutChar),
+         "b" (c)
+         : "%ecx", "%edx", "%esi", "%edi", "memory"
+     );