There's no real need for the associated probing - we can easily convert
to a uniform value without knowing the specific behavior (note also that
the respective comments weren't fully correct and have gone stale). All
we (need to) depend upon is unary ! producing 0 or 1 (and never -1).
For all present purposes yielding a value with all bits set is more
useful.
No difference in generated code.
Signed-off-by: Jan Beulich <jbeul...@suse.com>
---
Unlike in C, there's also binary ! in assembly expressions, and even
binary !!. But those don't get in the way here.
--- a/xen/arch/x86/arch.mk
+++ b/xen/arch/x86/arch.mk
@@ -26,10 +26,6 @@ $(call as-option-add,CFLAGS,CC,"invpcid
$(call as-option-add,CFLAGS,CC,"movdiri %rax$(comma)(%rax)",-DHAVE_AS_MOVDIR)
$(call as-option-add,CFLAGS,CC,"enqcmd (%rax)$(comma)%rax",-DHAVE_AS_ENQCMD)
-# GAS's idea of true is -1. Clang's idea is 1
-$(call as-option-add,CFLAGS,CC,\
- ".if ((1 > 0) < 0); .error \"\";.endif",,-DHAVE_AS_NEGATIVE_TRUE)
-
# Check to see whether the assmbler supports the .nop directive.
$(call as-option-add,CFLAGS,CC,\
".L1: .L2: .nops (.L2 - .L1)$(comma)9",-DHAVE_AS_NOPS_DIRECTIVE)
--- a/xen/arch/x86/include/asm/alternative.h
+++ b/xen/arch/x86/include/asm/alternative.h
@@ -35,19 +35,19 @@ extern void alternative_branches(void);
#define alt_repl_e(num) ".LXEN%=_repl_e"#num
#define alt_repl_len(num) "(" alt_repl_e(num) " - " alt_repl_s(num) ")"
-/* GAS's idea of true is -1, while Clang's idea is 1. */
-#ifdef HAVE_AS_NEGATIVE_TRUE
-# define AS_TRUE "-"
-#else
-# define AS_TRUE ""
-#endif
+/*
+ * GAS's idea of true is sometimes 1 and sometimes -1, while Clang's idea was
+ * consistently 1 up to 6.x (it matches GAS's now). Transform it to uniformly
+ * -1 (aka ~0).
+ */
+#define AS_TRUE "-!!"
-#define as_max(a, b) "(("a") ^ ((("a") ^ ("b")) & -("AS_TRUE"(("a") <
("b")))))"
+#define as_max(a, b) "(("a") ^ ((("a") ^ ("b")) & "AS_TRUE"(("a") < ("b"))))"
#define OLDINSTR(oldinstr, padding) \
".LXEN%=_orig_s:\n\t" oldinstr "\n .LXEN%=_orig_e:\n\t" \
".LXEN%=_diff = " padding "\n\t" \
- "mknops ("AS_TRUE"(.LXEN%=_diff > 0) * .LXEN%=_diff)\n\t" \
+ "mknops ("AS_TRUE"(.LXEN%=_diff > 0) & .LXEN%=_diff)\n\t" \
".LXEN%=_orig_p:\n\t"
#define OLDINSTR_1(oldinstr, n1) \
--- a/xen/arch/x86/include/asm/alternative-asm.h
+++ b/xen/arch/x86/include/asm/alternative-asm.h
@@ -29,17 +29,17 @@
#endif
.endm
-/* GAS's idea of true is -1, while Clang's idea is 1. */
-#ifdef HAVE_AS_NEGATIVE_TRUE
-# define as_true(x) (-(x))
-#else
-# define as_true(x) (x)
-#endif
+/*
+ * GAS's idea of true is sometimes 1 and sometimes -1, while Clang's idea was
+ * consistently 1 up to 6.x (it matches GAS's now). Transform it to uniformly
+ * -1 (aka ~0).
+ */
+#define as_true(x) (-!!(x))
#define decl_orig(insn, padding) \
.L\@_orig_s: insn; .L\@_orig_e: \
.L\@_diff = padding; \
- mknops (as_true(.L\@_diff > 0) * .L\@_diff); \
+ mknops (as_true(.L\@_diff > 0) & .L\@_diff); \
.L\@_orig_p:
#define orig_len (.L\@_orig_e - .L\@_orig_s)
@@ -49,7 +49,7 @@
#define decl_repl(insn, nr) .L\@_repl_s\()nr: insn; .L\@_repl_e\()nr:
#define repl_len(nr) (.L\@_repl_e\()nr - .L\@_repl_s\()nr)
-#define as_max(a, b) ((a) ^ (((a) ^ (b)) & -as_true((a) < (b))))
+#define as_max(a, b) ((a) ^ (((a) ^ (b)) & as_true((a) < (b))))
.macro ALTERNATIVE oldinstr, newinstr, feature
decl_orig(\oldinstr, repl_len(1) - orig_len)
