diff options
Diffstat (limited to '0056-x86-altcall-fix-clang-code-gen-when-using-altcall-in.patch')
| -rw-r--r-- | 0056-x86-altcall-fix-clang-code-gen-when-using-altcall-in.patch | 85 |
1 files changed, 85 insertions, 0 deletions
diff --git a/0056-x86-altcall-fix-clang-code-gen-when-using-altcall-in.patch b/0056-x86-altcall-fix-clang-code-gen-when-using-altcall-in.patch new file mode 100644 index 0000000..c94c516 --- /dev/null +++ b/0056-x86-altcall-fix-clang-code-gen-when-using-altcall-in.patch @@ -0,0 +1,85 @@ +From d078d0aa86e9e3b937f673dc89306b3afd09d560 Mon Sep 17 00:00:00 2001 +From: =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?= <roger.pau@citrix.com> +Date: Thu, 25 Jul 2024 16:21:17 +0200 +Subject: [PATCH 56/56] x86/altcall: fix clang code-gen when using altcall in + loop constructs +MIME-Version: 1.0 +Content-Type: text/plain; charset=UTF-8 +Content-Transfer-Encoding: 8bit + +Yet another clang code generation issue when using altcalls. + +The issue this time is with using loop constructs around alternative_{,v}call +instances using parameter types smaller than the register size. + +Given the following example code: + +static void bar(bool b) +{ + unsigned int i; + + for ( i = 0; i < 10; i++ ) + { + int ret_; + register union { + bool e; + unsigned long r; + } di asm("rdi") = { .e = b }; + register unsigned long si asm("rsi"); + register unsigned long dx asm("rdx"); + register unsigned long cx asm("rcx"); + register unsigned long r8 asm("r8"); + register unsigned long r9 asm("r9"); + register unsigned long r10 asm("r10"); + register unsigned long r11 asm("r11"); + + asm volatile ( "call %c[addr]" + : "+r" (di), "=r" (si), "=r" (dx), + "=r" (cx), "=r" (r8), "=r" (r9), + "=r" (r10), "=r" (r11), "=a" (ret_) + : [addr] "i" (&(func)), "g" (func) + : "memory" ); + } +} + +See: https://godbolt.org/z/qvxMGd84q + +Clang will generate machine code that only resets the low 8 bits of %rdi +between loop calls, leaving the rest of the register possibly containing +garbage from the use of %rdi inside the called function. Note also that clang +doesn't truncate the input parameters at the callee, thus breaking the psABI. + +Fix this by turning the `e` element in the anonymous union into an array that +consumes the same space as an unsigned long, as this forces clang to reset the +whole %rdi register instead of just the low 8 bits. + +Fixes: 2ce562b2a413 ('x86/altcall: use a union as register type for function parameters on clang') +Suggested-by: Jan Beulich <jbeulich@suse.com> +Signed-off-by: Roger Pau Monné <roger.pau@citrix.com> +Reviewed-by: Jan Beulich <jbeulich@suse.com> +master commit: d51b2f5ea1915fe058f730b0ec542cf84254fca0 +master date: 2024-07-23 13:59:30 +0200 +--- + xen/arch/x86/include/asm/alternative.h | 4 ++-- + 1 file changed, 2 insertions(+), 2 deletions(-) + +diff --git a/xen/arch/x86/include/asm/alternative.h b/xen/arch/x86/include/asm/alternative.h +index 0d3697f1de..e63b459276 100644 +--- a/xen/arch/x86/include/asm/alternative.h ++++ b/xen/arch/x86/include/asm/alternative.h +@@ -185,10 +185,10 @@ extern void alternative_branches(void); + */ + #define ALT_CALL_ARG(arg, n) \ + register union { \ +- typeof(arg) e; \ ++ typeof(arg) e[sizeof(long) / sizeof(arg)]; \ + unsigned long r; \ + } a ## n ## _ asm ( ALT_CALL_arg ## n ) = { \ +- .e = ({ BUILD_BUG_ON(sizeof(arg) > sizeof(void *)); (arg); }) \ ++ .e[0] = ({ BUILD_BUG_ON(sizeof(arg) > sizeof(void *)); (arg); })\ + } + #else + #define ALT_CALL_ARG(arg, n) \ +-- +2.45.2 + |