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stand: remove CLANG_NO_IAS from cdboot

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Many components under stand/ had CLANG_NO_IAS added when Clang's
Integrated Assembler (IAS) did not handle .codeNN directives.  Clang
gained support quite some time ago, and we can now build stand/ with
IAS.  In most cases IAS- and GNU as-assembled boot components were
identical, and CLANG_NO_IAS was already removed from other components.

Clang IAS produces different output for some components, including
cdboot, so CLANG_NO_IAS was not previously removed for those.

In the case of cdboot the difference is that IAS adds a size override
prefix (67h) to many instructions to specify a 32-bit address, even
though the two high bytes are zero.  This wastes three bytes per
instance, but as cdboot is not size-constrained it doesn't matter.
Padding is also different in one case; Clang used two one-byte nops
while GNU as used a single two-byte xchg %eax, %eax.  In any case, there
is no functional change.

Sponsored by:   The FreeBSD Foundation
This commit is contained in:
Ed Maste 2019-08-15 17:32:39 +00:00
parent 0b894a06bd
commit 1596e9a43c
1 changed files with 0 additions and 3 deletions
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3
stand/i386/cdboot/Makefile
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@ -14,6 +14,3 @@ ORG= 0x7c00
LDFLAGS+=${LDFLAGS_BIN} LDFLAGS+=${LDFLAGS_BIN}
.include <bsd.prog.mk> .include <bsd.prog.mk>
# XXX: clang integrated-as doesn't grok .codeNN directives yet
CFLAGS.cdboot.S= ${CLANG_NO_IAS}