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[librm] Clarify layout of saved GDTR/IDTR

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The separate VC_TMP_GDT and VC_TMP_IDT fields suggest that these could
be moved freely relative to each other.  This is not the case: callers
of prot_to_real() must pass a single pointer to the combined pair.

Collapse to a single field, with the name adjusted to VC_TMP_GDTR_IDTR
to more closely match the rm_default_gdtr_idtr structure that
necessarily shares the same layout.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
2026-09-06 15:13:38 +01:00
parent b57bc764a5
commit aef505b823
1 changed files with 5 additions and 6 deletions
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src/arch/x86/transitions/librm.S
+5 -6
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@@ -204,8 +204,7 @@ pm_esp: .long VIRTUAL(_estack)
*/
/* Temporary static buffer usage by virt_call */
.struct 0
VC_TMP_GDT: .space 6
VC_TMP_IDT: .space 6
VC_TMP_GDTR_IDTR: .space 12 /* must match rm_default_gdtr_idtr layout */
VC_TMP_PAD: .space 4 /* for alignment */
.if64
VC_TMP_CR3: .space 4
@@ -1023,9 +1022,9 @@ virt_call:
jz 1f
fxsave ( rm_tmpbuf + VC_TMP_FXSAVE )
1:
/* Preserve GDT and IDT in temporary static buffer */
sidt ( rm_tmpbuf + VC_TMP_IDT )
sgdt ( rm_tmpbuf + VC_TMP_GDT )
/* Preserve GDTR and IDTR in temporary static buffer */
sidt ( rm_tmpbuf + VC_TMP_GDTR_IDTR + 6 )
sgdt ( rm_tmpbuf + VC_TMP_GDTR_IDTR + 0 )
.if64 ; /* Preserve control registers, if applicable */
movl $MSR_EFER, %ecx
@@ -1071,7 +1070,7 @@ vc_lmode:
/* Switch to real mode and move register dump back to RM stack */
movl $VC_OFFSET_END, %ecx
movl $VC_TMP_END, %edx
leal VC_TMP_GDT(%esp, %ecx), %esi
leal VC_TMP_GDTR_IDTR(%esp, %ecx), %esi
pushl $vc_rmode
jmp prot_to_real
.section ".text16.virt_call", "ax", @progbits