[PATCH v2] Reduce assembly code size of exception entry points

[Frediano Ziglio <frediano.ziglio@cloud.com>]

We just pushed a 8-bytes zero and exception constants are
small so we can just write a single byte saving 3 bytes for
instruction.
With ENDBR64 this reduces the size of many entry points from 32 to
16 bytes (due to alignment).
Similar code is already used in autogen_stubs.

Signed-off-by: Frediano Ziglio <frediano.ziglio@cloud.com>
--
v2:
- added missing entry points;
- add mention to autogen_stubs code, as suggested.
---
 xen/arch/x86/x86_64/entry.S | 40 ++++++++++++++++++-------------------
 1 file changed, 20 insertions(+), 20 deletions(-)

diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S
index ecdd6e5b47..a28a0d4044 100644
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -389,7 +389,7 @@ FUNC(entry_int80)
         ENDBR64
         ALTERNATIVE "", clac, X86_FEATURE_XEN_SMAP
         pushq $0
-        movl  $0x80, 4(%rsp)
+        movb  $0x80, 4(%rsp)
         SAVE_ALL
 
         SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo, %rdx=0, Clob: acd */
@@ -653,7 +653,7 @@ END(ret_from_intr)
         .section .init.text, "ax", @progbits
 FUNC(early_page_fault)
         ENDBR64
-        movl  $X86_EXC_PF, 4(%rsp)
+        movb  $X86_EXC_PF, 4(%rsp)
         SAVE_ALL
         movq  %rsp, %rdi
         call  do_early_page_fault
@@ -898,105 +898,105 @@ END(handle_exception)
 FUNC(entry_DE)
         ENDBR64
         pushq $0
-        movl  $X86_EXC_DE, 4(%rsp)
+        movb  $X86_EXC_DE, 4(%rsp)
         jmp   handle_exception
 END(entry_DE)
 
 FUNC(entry_MF)
         ENDBR64
         pushq $0
-        movl  $X86_EXC_MF, 4(%rsp)
+        movb  $X86_EXC_MF, 4(%rsp)
         jmp   handle_exception
 END(entry_MF)
 
 FUNC(entry_XM)
         ENDBR64
         pushq $0
-        movl  $X86_EXC_XM, 4(%rsp)
+        movb  $X86_EXC_XM, 4(%rsp)
         jmp   handle_exception
 END(entry_XM)
 
 FUNC(entry_NM)
         ENDBR64
         pushq $0
-        movl  $X86_EXC_NM, 4(%rsp)
+        movb  $X86_EXC_NM, 4(%rsp)
         jmp   handle_exception
 END(entry_NM)
 
 FUNC(entry_DB)
         ENDBR64
         pushq $0
-        movl  $X86_EXC_DB, 4(%rsp)
+        movb  $X86_EXC_DB, 4(%rsp)
         jmp   handle_ist_exception
 END(entry_DB)
 
 FUNC(entry_BP)
         ENDBR64
         pushq $0
-        movl  $X86_EXC_BP, 4(%rsp)
+        movb  $X86_EXC_BP, 4(%rsp)
         jmp   handle_exception
 END(entry_BP)
 
 FUNC(entry_OF)
         ENDBR64
         pushq $0
-        movl  $X86_EXC_OF, 4(%rsp)
+        movb  $X86_EXC_OF, 4(%rsp)
         jmp   handle_exception
 END(entry_OF)
 
 FUNC(entry_BR)
         ENDBR64
         pushq $0
-        movl  $X86_EXC_BR, 4(%rsp)
+        movb  $X86_EXC_BR, 4(%rsp)
         jmp   handle_exception
 END(entry_BR)
 
 FUNC(entry_UD)
         ENDBR64
         pushq $0
-        movl  $X86_EXC_UD, 4(%rsp)
+        movb  $X86_EXC_UD, 4(%rsp)
         jmp   handle_exception
 END(entry_UD)
 
 FUNC(entry_TS)
         ENDBR64
-        movl  $X86_EXC_TS, 4(%rsp)
+        movb  $X86_EXC_TS, 4(%rsp)
         jmp   handle_exception
 END(entry_TS)
 
 FUNC(entry_NP)
         ENDBR64
-        movl  $X86_EXC_NP, 4(%rsp)
+        movb  $X86_EXC_NP, 4(%rsp)
         jmp   handle_exception
 END(entry_NP)
 
 FUNC(entry_SS)
         ENDBR64
-        movl  $X86_EXC_SS, 4(%rsp)
+        movb  $X86_EXC_SS, 4(%rsp)
         jmp   handle_exception
 END(entry_SS)
 
 FUNC(entry_GP)
         ENDBR64
-        movl  $X86_EXC_GP, 4(%rsp)
+        movb  $X86_EXC_GP, 4(%rsp)
         jmp   handle_exception
 END(entry_GP)
 
 FUNC(entry_AC)
         ENDBR64
-        movl  $X86_EXC_AC, 4(%rsp)
+        movb  $X86_EXC_AC, 4(%rsp)
         jmp   handle_exception
 END(entry_AC)
 
 FUNC(entry_CP)
         ENDBR64
-        movl  $X86_EXC_CP, 4(%rsp)
+        movb  $X86_EXC_CP, 4(%rsp)
         jmp   handle_exception
 END(entry_CP)
 
 FUNC(entry_DF)
         ENDBR64
-        movl  $X86_EXC_DF, 4(%rsp)
+        movb  $X86_EXC_DF, 4(%rsp)
         /* Set AC to reduce chance of further SMAP faults */
         ALTERNATIVE "", stac, X86_FEATURE_XEN_SMAP
         SAVE_ALL
@@ -1022,7 +1022,7 @@ END(entry_DF)
 FUNC(entry_NMI)
         ENDBR64
         pushq $0
-        movl  $X86_EXC_NMI, 4(%rsp)
+        movb  $X86_EXC_NMI, 4(%rsp)
 END(entry_NMI)
 
 FUNC(handle_ist_exception)
@@ -1158,7 +1158,7 @@ END(handle_ist_exception)
 FUNC(entry_MC)
         ENDBR64
         pushq $0
-        movl  $X86_EXC_MC, 4(%rsp)
+        movb  $X86_EXC_MC, 4(%rsp)
         jmp   handle_ist_exception
 END(entry_MC)
 
-- 
2.34.1