Unify return path for CSM to go via csm_return()

This allows us to keep the entry_csm code simple, and ensures that we
consistently do things like saving the PIC mask (and later setting
UmbStart) on the way back to UEFI.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

2 files changed, 22 insertions, 21 deletions

diff --git a/src/csm.c b/src/csm.c
index 40fbf5d8..45ca9419 100644
--- a/src/csm.c
+++ b/src/csm.c
@@ -34,7 +34,16 @@ EFI_COMPATIBILITY16_TABLE csm_compat_table VAR32FLATVISIBLE __aligned(16) = {
 EFI_TO_COMPATIBILITY16_INIT_TABLE *csm_init_table;
 EFI_TO_COMPATIBILITY16_BOOT_TABLE *csm_boot_table;
 
-extern void csm_return(struct bregs *regs) __noreturn;
+extern void __csm_return(struct bregs *regs) __noreturn;
+
+static void
+csm_return(struct bregs *regs)
+{
+    dprintf(3, "handle_csm returning AX=%04x\n", regs->ax);
+
+    pic_save_mask();
+    __csm_return(regs);
+}
 
 static void
 csm_maininit(struct bregs *regs)
@@ -47,9 +56,6 @@ csm_maininit(struct bregs *regs)
 
     regs->ax = 0;
 
-    // Return directly to UEFI instead of unwinding stack.
-    pic_save_mask();
-    dprintf(3, "csm_maininit fast returning AX=%04x\n", regs->ax);
     csm_return(regs);
 }
 
@@ -243,7 +249,7 @@ handle_csm(struct bregs *regs)
     if (!CONFIG_CSM)
         return;
 
-    dprintf(3, "handle_csm16 regs %p AX=%04x\n", regs, regs->ax);
+    dprintf(3, "handle_csm regs %p AX=%04x\n", regs, regs->ax);
 
     pic_restore_mask();
 
@@ -260,9 +266,7 @@ handle_csm(struct bregs *regs)
     default: regs->al = 1;
     }
 
-    pic_save_mask();
-
-    dprintf(3, "handle_csm16 returning AX=%04x\n", regs->ax);
+    csm_return(regs);
 }
 
 int csm_bootprio_ata(struct pci_device *pci, int chanid, int slave)
diff --git a/src/romlayout.S b/src/romlayout.S
index cbe6b1c6..2a2984cc 100644
--- a/src/romlayout.S
+++ b/src/romlayout.S
@@ -394,27 +394,24 @@ entry_csm:
         PUSHBREGS
 
         // Backup stack location and convert to a "flat pointer"
-        movl %ss, %ebx
-        movw %bx, BREGS_code+2(%esp)    // Store %ss in bregs->code.seg
-        shll $4, %ebx
-        addl %esp, %ebx
+        movl %ss, %eax
+        movw %ax, BREGS_code+2(%esp)    // Store %ss in bregs->code.seg
+        shll $4, %eax
+        addl %esp, %eax
 
         // Change to BUILD_STACK_ADDR stack
-        xorl %eax, %eax
-        movw %ax, %ss
+        xorl %ebx, %ebx
+        movw %bx, %ss
         movl $BUILD_STACK_ADDR, %esp
 
         // Jump to 32bit mode and call handle_csm(bregs)
-        movl $(1f + BUILD_BIOS_ADDR), %edx
+        movl $_cfunc32flat_handle_csm, %edx
         jmp transition32
+
         .code32
-1:      movl %ebx, %eax
-        calll _cfunc32flat_handle_csm - BUILD_BIOS_ADDR
-        movl $2f, %edx
-        jmp transition16big
 
-        .global csm_return
-csm_return:
+        EXPORTFUNC __csm_return
+__csm_return:
         movl %eax, %ebx
         movl $2f, %edx
         jmp transition16big