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From 722f59d38c710a940ab05e542a83020eb5546dea Mon Sep 17 00:00:00 2001
From: Jan Beulich <jbeulich@suse.com>
Date: Thu, 27 May 2021 14:40:29 +0200
Subject: [PATCH] x86: make hypervisor build with gcc11
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Gcc 11 looks to make incorrect assumptions about valid ranges that
pointers may be used for addressing when they are derived from e.g. a
plain constant. See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100680.
Utilize RELOC_HIDE() to work around the issue, which for x86 manifests
in at least
- mpparse.c:efi_check_config(),
- tboot.c:tboot_probe(),
- tboot.c:tboot_gen_frametable_integrity(),
- x86_emulate.c:x86_emulate() (at -O2 only).
The last case is particularly odd not just because it only triggers at
higher optimization levels, but also because it only affects one of at
least three similar constructs. Various "note" diagnostics claim the
valid index range to be [0, 2⁶³-1].
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Tested-by: Jason Andryuk <jandryuk@gmail.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
---
tools/tests/x86_emulator/x86-emulate.c | 7 +++++++
xen/arch/x86/x86_emulate/x86_emulate.c | 2 +-
xen/include/asm-x86/fixmap.h | 2 +-
xen/include/xen/compiler.h | 6 ++++++
xen/include/xen/pdx.h | 2 +-
5 files changed, 16 insertions(+), 3 deletions(-)
diff --git a/tools/tests/x86_emulator/x86-emulate.c b/tools/tests/x86_emulator/x86-emulate.c
index 07f892dbbb..ea286d6ad8 100644
--- a/tools/tests/x86_emulator/x86-emulate.c
+++ b/tools/tests/x86_emulator/x86-emulate.c
@@ -8,6 +8,13 @@
#define ERR_PTR(val) NULL
+/* See gcc bug 100680, but here don't bother making this version dependent. */
+#define gcc11_wrap(x) ({ \
+ unsigned long x_; \
+ __asm__ ( "" : "=g" (x_) : "0" (x) ); \
+ (typeof(x))x_; \
+})
+
#define cpu_has_amd_erratum(nr) 0
#define cpu_has_mpx false
#define read_bndcfgu() 0
diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c b/xen/arch/x86/x86_emulate/x86_emulate.c
index c25d88d0d8..31fdec030c 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -726,7 +726,7 @@ union vex {
#define copy_VEX(ptr, vex) ({ \
if ( !mode_64bit() ) \
(vex).reg |= 8; \
- (ptr)[0 - PFX_BYTES] = ext < ext_8f08 ? 0xc4 : 0x8f; \
+ gcc11_wrap(ptr)[0 - PFX_BYTES] = ext < ext_8f08 ? 0xc4 : 0x8f; \
(ptr)[1 - PFX_BYTES] = (vex).raw[0]; \
(ptr)[2 - PFX_BYTES] = (vex).raw[1]; \
container_of((ptr) + 1 - PFX_BYTES, typeof(vex), raw[0]); \
diff --git a/xen/include/asm-x86/fixmap.h b/xen/include/asm-x86/fixmap.h
index 0db314baeb..20746afd0a 100644
--- a/xen/include/asm-x86/fixmap.h
+++ b/xen/include/asm-x86/fixmap.h
@@ -78,7 +78,7 @@ extern void __set_fixmap(
#define clear_fixmap(idx) __set_fixmap(idx, 0, 0)
-#define __fix_to_virt(x) (FIXADDR_TOP - ((x) << PAGE_SHIFT))
+#define __fix_to_virt(x) gcc11_wrap(FIXADDR_TOP - ((x) << PAGE_SHIFT))
#define __virt_to_fix(x) ((FIXADDR_TOP - ((x)&PAGE_MASK)) >> PAGE_SHIFT)
#define fix_to_virt(x) ((void *)__fix_to_virt(x))
diff --git a/xen/include/xen/compiler.h b/xen/include/xen/compiler.h
index 17cf00e1ec..696c7eb89e 100644
--- a/xen/include/xen/compiler.h
+++ b/xen/include/xen/compiler.h
@@ -140,6 +140,12 @@
__asm__ ("" : "=r"(__ptr) : "0"(ptr)); \
(typeof(ptr)) (__ptr + (off)); })
+#if CONFIG_GCC_VERSION >= 110000 /* See gcc bug 100680. */
+# define gcc11_wrap(x) RELOC_HIDE(x, 0)
+#else
+# define gcc11_wrap(x) (x)
+#endif
+
#ifdef __GCC_ASM_FLAG_OUTPUTS__
# define ASM_FLAG_OUT(yes, no) yes
#else
diff --git a/xen/include/xen/pdx.h b/xen/include/xen/pdx.h
index 770fadc06c..9fcfb0ce52 100644
--- a/xen/include/xen/pdx.h
+++ b/xen/include/xen/pdx.h
@@ -19,7 +19,7 @@ extern u64 pdx_region_mask(u64 base, u64 len);
extern void set_pdx_range(unsigned long smfn, unsigned long emfn);
#define page_to_pdx(pg) ((pg) - frame_table)
-#define pdx_to_page(pdx) (frame_table + (pdx))
+#define pdx_to_page(pdx) gcc11_wrap(frame_table + (pdx))
bool __mfn_valid(unsigned long mfn);
--
2.25.1
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