[xen master] x86: control memset() and memcpy() inlining

[patchbot@xxxxxxx]

commit 50f3eb50613a7cc3f6d9aef7ea0c781d2db2607d
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Wed Jul 23 15:19:16 2025 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Jul 23 15:19:16 2025 +0200

    x86: control memset() and memcpy() inlining
    
    Stop the compiler from inlining non-trivial memset() and memcpy() (for
    memset() see e.g. map_vcpu_info() or kimage_load_segments() for
    examples). This way we even keep the compiler from using REP STOSQ /
    REP MOVSQ when we'd prefer REP STOSB / REP MOVSB (when ERMS is
    available).
    
    With gcc10 this yields a modest .text size reduction (release build) of
    around 2k.
    
    Unfortunately these options aren't understood by the clang versions I
    have readily available for testing with; I'm unaware of equivalents.
    
    Note also that using cc-option-add is not an option here, or at least I
    couldn't make things work with it (in case the option was not supported
    by the compiler): The embedded comma in the option looks to be getting
    in the way.
    
    Requested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Jason Andryuk <jason.andryuk@xxxxxxx>
---
 xen/arch/x86/arch.mk | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/xen/arch/x86/arch.mk b/xen/arch/x86/arch.mk
index 7e83935201..2c17dba754 100644
--- a/xen/arch/x86/arch.mk
+++ b/xen/arch/x86/arch.mk
@@ -61,6 +61,9 @@ endif
 $(call cc-option-add,CFLAGS_stack_boundary,CC,-mpreferred-stack-boundary=3)
 export CFLAGS_stack_boundary
 
+CFLAGS += $(call 
cc-option,$(CC),-mmemcpy-strategy=unrolled_loop:16:noalign$(comma)libcall:-1:noalign)
+CFLAGS += $(call 
cc-option,$(CC),-mmemset-strategy=unrolled_loop:16:noalign$(comma)libcall:-1:noalign)
+
 ifeq ($(CONFIG_UBSAN),y)
 # Don't enable alignment sanitisation.  x86 has efficient unaligned accesses,
 # and various things (ACPI tables, hypercall pages, stubs, etc) are wont-fix.
--
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