X-Git-Url: http://nsz.repo.hu/git/?a=blobdiff_plain;f=src%2Finternal%2Fi386%2Fsyscall.s;h=2914aceeb9f779c1055692c30b550aaf4bc0f228;hb=HEAD;hp=79296ba02c9b226928d90f5c7dd8b6f2484e8c85;hpb=12e9b4faf68a1a02ebf5ad69c03ac10f170f14cb;p=musl

diff --git a/src/internal/i386/syscall.s b/src/internal/i386/syscall.s
index 79296ba0..2914acee 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:
@@ -10,7 +16,8 @@ __vsyscall:
 	mov 12(%esp),%edi
 	push %eax
 	call 1f
-2:	pop %ebx
+2:	mov %ebx,%edx
+	pop %ebx
 	pop %ebx
 	pop %edi
 	ret
@@ -22,11 +29,17 @@ __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: