From: Nick Desaulniers <ndesaulniers@google.com>
To: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>
Cc: x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Nathan Chancellor <nathan@kernel.org>, Tom Rix <trix@redhat.com>,
Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
Adrian Hunter <adrian.hunter@intel.com>,
Josh Poimboeuf <jpoimboe@kernel.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Daniel Sneddon <daniel.sneddon@linux.intel.com>,
Sandipan Das <sandipan.das@amd.com>,
Huang Rui <ray.huang@amd.com>,
linux-kernel@vger.kernel.org, llvm@lists.linux.dev,
kernel-team@android.com,
Nick Desaulniers <ndesaulniers@google.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: [PATCH] x86/msr-index: make SPEC_CTRL_IBRS assembler-portable
Date: Thu, 3 Nov 2022 14:07:48 -0700 [thread overview]
Message-ID: <20221103210748.1343090-1-ndesaulniers@google.com> (raw)
GNU binutils' assembler (GAS) didn't support L suffixes on immediates
until binutils 2.28 release. Building arch/x86/entry/entry_64.S with GAS
v2.27 will produce the following assembler errors:
arch/x86/entry/entry_64.S: Assembler messages:
arch/x86/entry/entry_64.S:308: Error: found 'L', expected: ')'
arch/x86/entry/entry_64.S:308: Error: found 'L', expected: ')'
arch/x86/entry/entry_64.S:308: Error: junk `L<<(0)))' after expression
arch/x86/entry/entry_64.S:596: Error: found 'L', expected: ')'
arch/x86/entry/entry_64.S:596: Error: found 'L', expected: ')'
arch/x86/entry/entry_64.S:596: Error: junk `L<<(0)))' after expression
These come from the use of the preprocessor defined SPEC_CTRL_IBRS in
the IBRS_ENTER and IBRS_EXIT assembler macros. SPEC_CTRL_IBRS was using
the BIT macros from include/linux/bits.h which are only portable between
C and assembler for assemblers such as GAS v2.28 (or newer) or clang
because they use the L suffixes for immediate operands, which older GAS
releases cannot parse. The kernel still supports GAS v2.23 and newer
(and older for branches of stable). Let's expand the value of
SPEC_CTRL_IBRS in place so that assemblers don't have issues parsing the
value.
Fixes: 2dbb887e875b ("x86/entry: Add kernel IBRS implementation")
Reported-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
Some other ideas considered:
* Use U64_C from include/asm-generic/int-ll64.h rather than BIT for the
value of SPEC_CTRL_IBRS.
* Do so for the entirety of arch/x86/include/asm/msr-index.h or just
SPEC_CTRL_IBRS? include/asm-generic/int-ll64.h doesn't define a UL
suffix; add one?
* Make include/linux/bits.h assembler-portable (for older assemblers)
via the use of include/asm-generic/int-ll64.h.
arch/x86/include/asm/msr-index.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 10ac52705892..0192d853136c 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -46,7 +46,7 @@
#define MSR_TEST_CTRL_SPLIT_LOCK_DETECT BIT(MSR_TEST_CTRL_SPLIT_LOCK_DETECT_BIT)
#define MSR_IA32_SPEC_CTRL 0x00000048 /* Speculation Control */
-#define SPEC_CTRL_IBRS BIT(0) /* Indirect Branch Restricted Speculation */
+#define SPEC_CTRL_IBRS 1 /* Indirect Branch Restricted Speculation */
#define SPEC_CTRL_STIBP_SHIFT 1 /* Single Thread Indirect Branch Predictor (STIBP) bit */
#define SPEC_CTRL_STIBP BIT(SPEC_CTRL_STIBP_SHIFT) /* STIBP mask */
#define SPEC_CTRL_SSBD_SHIFT 2 /* Speculative Store Bypass Disable bit */
--
2.38.1.431.g37b22c650d-goog
next reply other threads:[~2022-11-03 21:10 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-03 21:07 Nick Desaulniers [this message]
2022-11-04 9:55 ` [PATCH] x86/msr-index: make SPEC_CTRL_IBRS assembler-portable H. Peter Anvin
2022-11-04 18:07 ` Nick Desaulniers
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20221103210748.1343090-1-ndesaulniers@google.com \
--to=ndesaulniers@google.com \
--cc=adrian.hunter@intel.com \
--cc=alexander.shishkin@linux.intel.com \
--cc=bp@alien8.de \
--cc=daniel.sneddon@linux.intel.com \
--cc=dave.hansen@linux.intel.com \
--cc=gregkh@linuxfoundation.org \
--cc=hpa@zytor.com \
--cc=jpoimboe@kernel.org \
--cc=kernel-team@android.com \
--cc=linux-kernel@vger.kernel.org \
--cc=llvm@lists.linux.dev \
--cc=mingo@redhat.com \
--cc=nathan@kernel.org \
--cc=pawan.kumar.gupta@linux.intel.com \
--cc=peterz@infradead.org \
--cc=ray.huang@amd.com \
--cc=sandipan.das@amd.com \
--cc=tglx@linutronix.de \
--cc=trix@redhat.com \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).