| Message ID | 20200414163255.66437-1-maskray@google.com (mailing list archive) |
|---|---|
| State | Mainlined |
| Commit | c9a4ef66450145a356a626c833d3d7b1668b3ded |
| Headers | show |
| Series | [v2] arm64: Delete the space separator in __emit_inst | expand |
On Tue, Apr 14, 2020 at 09:32:55AM -0700, Fangrui Song wrote: > In assembly, many instances of __emit_inst(x) expand to a directive. In > a few places __emit_inst(x) is used as an assembler macro argument. For > example, in arch/arm64/kvm/hyp/entry.S > > ALTERNATIVE(nop, SET_PSTATE_PAN(1), ARM64_HAS_PAN, CONFIG_ARM64_PAN) > > expands to the following by the C preprocessor: > > alternative_insn nop, .inst (0xd500401f | ((0) << 16 | (4) << 5) | ((!!1) << 8)), 4, 1 > > Both comma and space are separators, with an exception that content > inside a pair of parentheses/quotes is not split, so the clang > integrated assembler splits the arguments to: > > nop, .inst, (0xd500401f | ((0) << 16 | (4) << 5) | ((!!1) << 8)), 4, 1 > > GNU as preprocesses the input with do_scrub_chars(). Its arm64 backend > (along with many other non-x86 backends) sees: > > alternative_insn nop,.inst(0xd500401f|((0)<<16|(4)<<5)|((!!1)<<8)),4,1 > # .inst(...) is parsed as one argument > > while its x86 backend sees: > > alternative_insn nop,.inst (0xd500401f|((0)<<16|(4)<<5)|((!!1)<<8)),4,1 > # The extra space before '(' makes the whole .inst (...) parsed as two arguments > > The non-x86 backend's behavior is considered unintentional > (https://sourceware.org/bugzilla/show_bug.cgi?id=25750). > So drop the space separator inside `.inst (...)` to make the clang > integrated assembler work. > > Suggested-by: Ilie Halip <ilie.halip@gmail.com> > Signed-off-by: Fangrui Song <maskray@google.com> > Reviewed-by: Mark Rutland <mark.rutland@arm.com> > Link: https://github.com/ClangBuiltLinux/linux/issues/939 Queued for 5.7. Thanks.
diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h index ebc622432831..c4ac0ac25a00 100644 --- a/arch/arm64/include/asm/sysreg.h +++ b/arch/arm64/include/asm/sysreg.h @@ -49,7 +49,9 @@ #ifndef CONFIG_BROKEN_GAS_INST #ifdef __ASSEMBLY__ -#define __emit_inst(x) .inst (x) +// The space separator is omitted so that __emit_inst(x) can be parsed as +// either an assembler directive or an assembler macro argument. +#define __emit_inst(x) .inst(x) #else #define __emit_inst(x) ".inst " __stringify((x)) "\n\t" #endif
In assembly, many instances of __emit_inst(x) expand to a directive. In a few places __emit_inst(x) is used as an assembler macro argument. For example, in arch/arm64/kvm/hyp/entry.S ALTERNATIVE(nop, SET_PSTATE_PAN(1), ARM64_HAS_PAN, CONFIG_ARM64_PAN) expands to the following by the C preprocessor: alternative_insn nop, .inst (0xd500401f | ((0) << 16 | (4) << 5) | ((!!1) << 8)), 4, 1 Both comma and space are separators, with an exception that content inside a pair of parentheses/quotes is not split, so the clang integrated assembler splits the arguments to: nop, .inst, (0xd500401f | ((0) << 16 | (4) << 5) | ((!!1) << 8)), 4, 1 GNU as preprocesses the input with do_scrub_chars(). Its arm64 backend (along with many other non-x86 backends) sees: alternative_insn nop,.inst(0xd500401f|((0)<<16|(4)<<5)|((!!1)<<8)),4,1 # .inst(...) is parsed as one argument while its x86 backend sees: alternative_insn nop,.inst (0xd500401f|((0)<<16|(4)<<5)|((!!1)<<8)),4,1 # The extra space before '(' makes the whole .inst (...) parsed as two arguments The non-x86 backend's behavior is considered unintentional (https://sourceware.org/bugzilla/show_bug.cgi?id=25750). So drop the space separator inside `.inst (...)` to make the clang integrated assembler work. Suggested-by: Ilie Halip <ilie.halip@gmail.com> Signed-off-by: Fangrui Song <maskray@google.com> Reviewed-by: Mark Rutland <mark.rutland@arm.com> Link: https://github.com/ClangBuiltLinux/linux/issues/939 --- arch/arm64/include/asm/sysreg.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)