x86: make hypervisor build with gcc11

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>
master commit: 722f59d38c710a940ab05e542a83020eb5546dea
master date: 2021-05-27 14:40:29 +0200

diff --git a/tools/tests/x86_emulator/x86-emulate.c b/tools/tests/x86_emulator/x86-emulate.c
index 8132fe7a7ca84ada75bf2a29b91983e4d6115f57..dc098c9e068e450fc1b68eb31254281ca5ec5a38 100644 (file)
--- a/tools/tests/x86_emulator/x86-emulate.c
+++ b/tools/tests/x86_emulator/x86-emulate.c
@@ -2,6 +2,13 @@
 
 #include <sys/mman.h>
 
+/* 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 c7c55fa5722bc6b9e2ed8ce3c45fb1420072d4cd..88456bec9ed57ae9691f950e1ce95d2e0df5943b 100644 (file)
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -644,7 +644,7 @@ 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 16ccaa2c771f7aaa86922249b9e3eb86b187cc84..d460b71f4fc0ea722887f86c767467a5459ed6df 100644 (file)
--- a/xen/include/asm-x86/fixmap.h
+++ b/xen/include/asm-x86/fixmap.h
@@ -80,7 +80,7 @@ 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 ff6c0f5cdd18fdde1305a53c108304d1bf70e6c2..b1c0374dfe9859cabd3bd3ca42b9e74cbe4994ec 100644 (file)
--- a/xen/include/xen/compiler.h
+++ b/xen/include/xen/compiler.h
@@ -99,6 +99,12 @@
     __asm__ ("" : "=r"(__ptr) : "0"(ptr));      \
     (typeof(ptr)) (__ptr + (off)); })
 
+#if __GNUC__ >= 11 /* 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 a151aac1a228cd02084b783b1d7a07456404178d..5ed51b5edbbb442b24e567ca1328a4183a0b6c89 100644 (file)
--- 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);