[syslinux:master] com32: make __farcall() IF-preserving

[syslinux-bot for H. Peter Anvin]

Commit-ID:  859ead0a2ef7dfd0b5622ad4878dda1b26c22e29
Gitweb:     http://syslinux.zytor.com/commit/859ead0a2ef7dfd0b5622ad4878dda1b26c22e29
Author:     H. Peter Anvin <hpa at linux.intel.com>
AuthorDate: Mon, 21 Jun 2010 15:58:57 -0700
Committer:  H. Peter Anvin <hpa at linux.intel.com>
CommitDate: Mon, 21 Jun 2010 15:58:57 -0700

com32: make __farcall() IF-preserving

Make __farcall preserve the current value of IF.  If we need to we can
create a __raw_farcall() operation which does not.

Signed-off-by: H. Peter Anvin <hpa at linux.intel.com>


---
 com32/lib/sys/farcall.c |   15 ++++++++++++++-
 1 files changed, 14 insertions(+), 1 deletions(-)

diff --git a/com32/lib/sys/farcall.c b/com32/lib/sys/farcall.c
index 7d195f1..988ee6d 100644
--- a/com32/lib/sys/farcall.c
+++ b/com32/lib/sys/farcall.c
@@ -4,8 +4,21 @@
 
 #include <com32.h>
 
+static inline uint32_t eflags(void)
+{
+    uint32_t v;
+
+    asm volatile("pushfl ; popl %0" : "=rm" (v));
+    return v;
+}
+
 void __farcall(uint16_t cs, uint16_t ip,
 	       const com32sys_t * ireg, com32sys_t * oreg)
 {
-    __com32.cs_farcall((cs << 16) + ip, ireg, oreg);
+    com32sys_t xreg = *ireg;
+
+    /* Enable interrupts if and only if they are enabled in the caller */
+    xreg.eflags.l = (xreg.eflags.l & ~EFLAGS_IF) | (eflags() & EFLAGS_IF);
+
+    __com32.cs_farcall((cs << 16) + ip, &xreg, oreg);
 }