X-Git-Url: http://nsz.repo.hu/git/?p=musl;a=blobdiff_plain;f=src%2Finternal%2Fi386%2Fsyscall.s;h=291168c3240b55007132d4d479936b378d22fd78;hp=79296ba02c9b226928d90f5c7dd8b6f2484e8c85;hb=216dca82f6948627f55a0a04ab7d63a12213d8ed;hpb=12e9b4faf68a1a02ebf5ad69c03ac10f170f14cb

diff --git a/src/internal/i386/syscall.s b/src/internal/i386/syscall.s
index 79296ba0..291168c3 100644
--- a/src/internal/i386/syscall.s
+++ b/src/internal/i386/syscall.s
@@ -1,5 +1,11 @@
 .hidden __sysinfo
 
+# The calling convention for __vsyscall has the syscall number
+# and 5 args arriving as:  eax, edx, ecx, edi, esi, 4(%esp).
+# This ensures that the inline asm in the C code never has to touch
+# ebx or ebp (which are unavailable in PIC and frame-pointer-using
+# code, respectively), and optimizes for size/simplicity in the caller.
+
 .global __vsyscall
 .type __vsyscall,@function
 __vsyscall:
@@ -22,11 +28,17 @@ __vsyscall:
 	jz 1f
 	push %eax
 	mov 8(%esp),%eax
-	ret
+	ret                     # tail call to kernel vsyscall entry
 1:	mov 4(%esp),%eax
 	int $128
 	ret
 
+# The __vsyscall6 entry point is used only for 6-argument syscalls.
+# Instead of passing the 5th argument on the stack, a pointer to the
+# 5th and 6th arguments is passed. This is ugly, but there are no
+# register constraints the inline asm could use that would make it
+# possible to pass two arguments on the stack.
+
 .global __vsyscall6
 .type __vsyscall6,@function
 __vsyscall6: